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College  of  l^f)piitiani  anb  burgeons! 


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LIST  OF  CONTRIBUTORS. 


BURCHARD,  HENRY  H.,  M.D.,  D.D.S. 
ESSIG,  CHARLES  J.,  M.D.,  D.D.S. 
GRITMAN,  A.  DeWITT,  D.D.S. 
HILLYER,  ELLISON,  D.D.S. 
HODGEN,  JOSEPH  D.,  D.D.S. 
LeCRON,  D.  O.  M.,  M.D.,  D.D.S. 
OTTOLENGUI,  RODRIGUES,  M.D.S. 
PEESO,  FRED  A.,  D.D.S. 
THOMPSON,  ALTON  H.,  D.D.S. 
TRUEMAN,  WILLIAM  H.,  D.D.S. 
TURNER,  CHARLES  R.,  D.D.S.,  M.D. 
WILSON,  GEORGE  H.,  D.D.S. 


THE 


AMERICAN  TEXT-BOOK 


OP 


PROSTHETIC  DENTISTRY. 


IN  CONTRIBUTIONS  BY  EMINENT  AUTHOBITIES. 


EDITED  BY 

CHARLES  R.  TURNER,  D.D.S.,  M.D., 

PROFESSOR  OF  MECHANICAL  DENTISTRY    AND   METALLURGY,   DEPARTMENT  OF  DENTISTRY, 
UNIVERSITY  OF   PENNSYLVANIA,    PHILADELPHIA. 


FOURTH  EDITION,  REVISED  AND  ENLARGED. 
ILLUSTRATED    WITH    900    ENGRAVINGS 


LEA    &    FEBIGER 

PHILADELPHIA   AND   NEW   YORK 
1913 


/^/ 


'O 


Entered  according  to  Act  of  Congress,  in  the  year  1913,  by 

LEA  &  FEBIGER 

in  the  Office  of  the  Librarian  of  Congress.     All  rights  reserved. 


WITH   THE 

CORDIAL  CONSENT    OF  THE    CONTRIBUTORS 

THIS   VOLUME  IS  DEDICATED  TO 

EDWARD  CAMERON  KIRK,  D.D.S.,  Sc.D., 

IN   RECOGNITION    OF  HIS  EMINENCE  IN  DENTAL  LITERATURE 
SCIENCE,  AND    EDUCATION 

AND  AS  A 

MODEST  TOKEN  OF  THE  REGARD  OF  HIS  FRIEND  AND  COLLEAGUE 

THE  EDITOR. 


PREFACE  TO  FOURTH  EDITION. 


The  editor  offers  a  new  edition  of  the  American  Text-hook  of  Pros- 
thetic Dentistry  in  the  hope  that  it  may  continue  to  fill  the  important 
})lace  accorded  it  for  so  long  a  time  by  the  teachers,  students,  and  prac- 
titioners of  dentistry  in  this  country.  Being  intermediate  in  character 
between  the  hand-book,  which  is  intended  to  furnish  the  main  facts 
upon  a  subject  briefly  and  succinctly,  and  the  work  of  reference,  which 
as  a  final  authority  must  give  an  exhaustive  treatise  upon  its  topic,  the 
book  is  primarily  designed  as  a  teaching  volume.  It  stands  for  and  ad- 
heres to  the  general  pedagogical  principle  that  a  thorough  knowledge 
of  the  fundamental  principles  of  the  subject  must  first  be  inculcated, 
so  that  the  student  may  attack  his  problems  by  the  analytical  method 
instead  of  by  rote  or  authority.  After  this  foundational  knowledge 
is  obtained,  the  technical  procedures  necessary  to  construct  the  various 
appliances  employed  in  prosthetic  dentistry  may  be  undertaken,  instead 
of  making  the  latter  first  in  time  and  importance — a  point  of  view  not 
in  vogue  when  prosthetic  teaching  was  conducted  empirically  in  the 
dental  laboratory.  That  this  method  has  been  in  accord  with  the 
present  pedagogical  practice  is  attested  by  the  fact  of  the  widespread 
adoption  of  the  book  as  a  text-book  in  the  colleges  of  this  country. 

To  the  dental  practitioner  it  is  hoped  the  technical  teaching  will 
appeal  as  being  an  exposition  of  the  most  recent  approved  methods  of 
prosthetic  practice.  The  plan  of  composite  authorship  permits  the 
selection  of  men  who  have  given  special  attention  to  the  several  subjects 
of  which  the}^  treat. 

Since  the  appearance  of  the  last  edition  in  no  field  of  dentistry  has 
more  gratifying  progress  been  made  than  in  the  increase  of  our  knowledge 
upon  the  subject  of  the  so-called  "anatomical  articulation"  of  artificial 
teeth.  A  broader  knowledge  of  the  natural  masticating  mechanism, 
greater  accuracy  in  the  articulators  serving  to  represent  a  part  of  this 
mechanism,  and  vast  improvements  by  the  manufacturers  in  the  de- 
signs of  artificial  teeth  themselves  have  resulted  from  the  activities  of 
various  ones  concerned  in  treating  this  general  problem.  These  facts 
have  necessitated  an  enlargement  of  the  text  upon  these  several  topics 
in  order  that  it  may  embrace  such  details  of  these  subjects  as  seem  to  be 
proved  and  established.  While  in  none  of  them  has  the  "ultima  thule" 
been  reached,  there  is  a  great  general  improvement  in  the  scientific 
accuracy  of  our  knowledge  of  the  whole  question. 

The  chapter  on  Cast  Metal  Defitures,  written  by  the  late  Dr.  Clark  L. 
Goddard,  has  not  been  replaced  by  a  new  one  upon  the  subject.  Since 
the  extensive  employment  in  dentistry  within  the  past  few  years  of  the 
principle  of  casting  metals  under  pressure,  the  use  of  the  precious 

(vii) 


vm  PREFACE  TO  FOURTH  FD/TION. 

metals  for  base-plates  by  this  plan  has  proved  universally  (lisai)point- 
ing,  and  none  of  the  teehnic  so  far  evolved  can  be  recommended  to  the 
practitioner  or  student.  The  percentage  of  shrinkage  and  warpage  of 
the  metal  when  cast  in  large  masses,  its  lower  density  and  poorer  texture 
than  the  swaged  plate,  and  the  general  lack  of  uniformity  of  results 
have  all  pro\ed  obstacles  to  those  who  demand  accuracy  in  the  finished 
product.  While  the  methods  of  casting  aluminum  and  the  base  metal 
alloys  have  all  undergone  improvement,  it  is  not  felt  that  anything 
authoritative  can  be  given  on  this  toj)ic  at  this  stage  of  its  de^■elol)nu•nt. 
It  is  believed  that  many  of  the  defects  of  this  method  that  held  so 
much  of  promise  to  the  prosthetic  dentist  may  in  time  be  o\crcome  and 
its  field  of  u^s('fulness  extended. 

The  technical  details  of  metallurgical  operations  as  regards  obtaining 
the  metals  from  their  ores  and  all  others  not  directly  related  to  the 
practice  of  prosthesis  in  the  laboratory  have  been  omitted  from  the 
present  chapter  on  the  subject.  As  the  workman  must  know  his  tools, 
so  must  he  know  the  properties  of  the  materials  of  which  his  products 
are  wrought,  but  other  details,  interesting  and  important  as  they  are, 
must  be  reserved  for  the  separate  work  on  metallurgy. 

The  chapters  originally  contributed  by  Dr.  H.  H.  Burchard  on 
Tlic  E.vcuni nation  of  the  Mouth,  The  Taking  of  luijiirssions,  and  The 
Makincj  of  Piaster  Casis,  and  revised  by  the  late  Dr.  J.  P.  Gray,  whose 
loss  by  death  the  staff  of  contributors  has  suffered  since  the  last  edition 
appeared,  ha\e  been  replaced  by  chapters  on  these  subjects  by  Dr.  A. 
De  Witt  Gritman.  The  remaining  chapters  by  Dr.  Burchard  and 
those  by  Dr.  Essig  have  been  thoroughly  revised. 

In  acknowletlging  his  indebtedness  to  the  publishers  for  their  unfail- 
ing kindness  and  valuable  assistance  during  the  preparation  of  this 
^•olume,  the  editor  especially  wishes  to  express  his  appreciation  of  the 
sympathetic  help  of  ]\Ir.  Christian  Febiger,  with  whom  he  has  had  the 
privilege  of  manv  conferences  in  the  progress  of  the  work. 

C.  R.  T. 

3930  Locust  Street, 
Philadelphia. 


LIST  OF  CONTRIBUTORS. 


HENRY  H.  BURCHARD,  M.D,  D.D.S. 

Late  Special  Lecturer  on  Dental  Pathology  and  Therapeutics,  Philadelphia 
Dental  College,  Philadelphia. 

CHARLES  J.  ESSIG,  M.D.,  D.D.S. 

Late  Professor  of  Mechanical  Dentistry  and  Metallurgy,  Department  of 
Dentistry,  University  of  Pennsylvania,  Philadelphia. 

A.  DeWITT  GRITMAN,  D.D.S. 

Assistant  Professor  of  Prosthetic  Dentistry,  Department  of  Dentistry,  ITni- 
versity  of  Pennsylvania,  Philadelphia. 

ELLISON  HILLYER,  D.D.S. 

Professor  of  Prosthetic  Dentistry  and  Orthodontia  in  New  York  College  of 
Dentistry,  New  York  City. 

JOSEPH  D.  HODGEN,  D.D.S. 

Professor  of  Chemistry  and  Metallurgy,  College  of  Dentistry,  University  of 
California,  San  Francisco. 

D.  O.  M.  LeCRON,  M.D.,  D.D.S. 

Professor  of  Crown  and  Bridge-work  and  Porcelain  Dental  Art,  Barnes  Dental 
College,  St.  Louis,  Mo. 

RODRIGUES  OTTOLENGUI,  m.d.s. 

Editor  of  the  "Items  of  Interest." 

FRED  A.  PEESO,  D.D.S. 

Assistant  Professor  of  Crown  and  Bridge-work,  Department  of  Dentistry, 
University  of  Pennsylvania,  Philadelphia;  Professor  of  Crown  and  Bridge- 
work,  University  of  Pennsylvania  Dental  Post-Graduate  School. 

ALTON  HOWARD  THOMPSON,  D.D.S. 

Professor  of  Dental  Anatomy,  Kansas  City  Dental  College,  Kansas  City,  Mo. 

(ix) 


X  LIST  OF  CONTRIliUTORS. 

WILLIAM  H.  TRUEMAX,  D.D.S. 
Philadelphia,  Pu. 

CHARLES  R.  TURNER,  D.D.S.,  M.D. 

Professor  of  Mechanical  Dentistry  and  Metallurgy,  Department  of  Dentistry, 
Universitj^  of  Pennsylvania,  Philadelphia. 

GEORGE  H.  WILSON,  D.D.S. 

Formerly  Professor  of  Prosthetic  Dentistry  and  Metallurgy,  Dental  Depart- 
ment, Western  Reserve  Universitj',  Cleveland,  Oliio. 


CONTENTS. 


CHAPTER  I 

PAGE 

THE  DENTAL  LABORATORY:  ITS  EQUIPMENT  AND  ARRANGE- 
MENT   17 

By  Charles  J.  Essig,  M.D.,  D.D.S.,  and  Charles  R.  Turner,  D.D.S.,  M.D. 


CHAPTER  II. 

METALS  AND  ALLOYS  USED  IN  PROSTHETIC  DENTISTRY 91 

By  Joseph  Dupxjy  Hodgen,  D.D.S. 

CHAPTER  HI. 
PORCELAIN  TEETH 161 

By  Charles  J.  Essig,  M.D.,  D.D.S.  Revised  by  Ellison  Hillyer,  D.D.S. 

CHAPTER  IV. 

THE  HUMAN  DENTAL  MECHANISM:  ITS  STRUCTURE,  FUNCTIONS, 

AND  RELATIONS 192 


By  Charles  R.  Turner,  D.D.S.,  M.D. 


CHAPTER  V. 


THE  HUMAN  DENTAL  MECHANISM  AS  MODIFIED  BY  TEMPERA- 
MENT, AGE,  AND  USE 2.55 

By  Alton  H.  Thompson,  D.D.S.,  and  Charles  R.  Turner,  D.D.S.,  M.D. 


CHAPTER  VI. 

THE  EXl^MINATION,  PREPARATION,  AND  STUDY  OF  THE  MOUTH 

PRELIMINARY  TO  THE  INSERTION  OF  ARTIFICIAL  TEETH.  .  271 

By  a.  DeWitt  Gritman,  D.D.S. 


CHAPTER  VII. 

IMPRESSIONS  OF  THE  MOUTH 282 

By  a.  DeWitt  Gritman,  D.D.S. 

(xi) 


Xll  CONTENTS. 

CHAPTER  Mil. 

PAGE 

THE  MAKING  OF  PLASTER  CASTS 302 

By  a.  DEWirr  Guitmax,  D.D.S. 

CHAPTER  IX. 

DIES,  COUNTER-DIES,  AND  MOLDING 310 

By  William  H.  Trueman,  D.D.S. 

CHAPTER  X. 

SECURING  THE  VARIOUS  DATA  TO  BE  USED  IN  CONSTRT'CTING 
ARTIFICIAL  DENTURES.  TAKING  THE  BITE.  ARTICULA- 
TORS   335 

By  Charles  R.  Turner,  D.D.S.,  M.D. 

CHAPTER  XI. 

THE    PRINCIPLES    UNDERLYING    THE    RETENTION    OF    PLATE 

DENTURES 386 

By  Charles  R.  Turner,  D.D.S.,  M.D. 

CHAPTER  XII. 

THE  SELECTION,  ARRANGEMENT,  AND  ARTICULATION  OF  ARTI- 
FICIAL TEETH 407 

By  Charles  R.  Turner.  D.D.S.,  M.D. 

CHAPTER  XIII. 

VULCANIZED  RUBBER  AS  A  BASE  FOR  ARTIFICIAL  DENTURES..   472 

By  George  H.  Wilson,  D.D.S. 

CHAPTER  XIV. 

SWAGED  METALLIC  PLATES 649 

By  William  H.  Trueman,  D.D.S. 

CHAPTER  XV. 

CONTINUOUS-GUM  DENTT^RES 635 

By  D.  O.  M.  LeCron,  M.D.,  D.D.S. 

CHAPTER  XVI. 

ARTIFICIAL  CROWNS 661 

By  Henry  H.  Burchard,  M.D.,  D.D.S.,  and  Fred.  A.  Peeso,  D.D.S. 


CONTENTS.  xiii 

CHAPTER  XVII. 

AN  ASSEMBLAGE  OF  UNITED  CROWNS  (BRIDGE-WORK) 725 

By  IIenuy  H.  Burchaud,  M.D.,  D.D.S.,  and  Fued.  A.  Peeso,  D.D.S. 

CHAPTER  XVIII 

HYGIENIC  RELATIONS  AND  CARE  OF  ARTIFICIAL  DENTURES .      775 

By  Charles  J.  Essig,  M.D.,  D.D.S. 

CHAPTER  XIX. 

PALATAL  MECHANISM 786 

By  Rodrigues  Ottolengut,  M.D.S. 


PROSTHETIC     DENTISTRY, 


CHAPTER    I. 

THE  DENTAL  LABORATORY,  ITS  EQUIPMENT  AND  ARRANGEMENT,, 
By  Charles  J.  Essig,  M.D..  D.D.S. 

AND 

Charles  R.  Turner,  D.D.S.,  M.D. 
THE  LABORATORY. 

It  is  higlily  important  that  the  mechanical  laboratory  should  be 
suitably  arranged  and  equipped  for  the  purposes  to  which  it  is  devoted. 
In  planning  the  dental  offices  a  room  should  be  selected  which  is  appro- 
priate in  size  and  location.  It  frequently  happens  that  the  labora- 
tory is  relegated  to  a  room  which  cannot  be  used  for  other  purposes,  and 
which  answers  the  requirements  of  a  workshop  in  no  degree.  It  should 
be  easily  accessible  from  the  operating  room  to  facilitate  such  opera- 
tions as  band-fitting  for  crowns  which  are  partly  performed  in  both 
places.  From  a  hundred  to  a  hundred  and  fifty  feet  of  iioor  space 
are  necessary  for  one  or  two  workmen,  and  an  advantage  will  be  gained 
if  the  room  is  situated  with  its  longest  side  toward  the  light.  The 
uniformity  of  illumination  afforded  by  a  northern  light  recommends 
this  exposure  where  it  is  obtainable.  Ample  light  should  be  provided 
by  sufficient  window  space  so  that  none  of  the  laboratory  operations 
are  required  to  be  performed  in  shadow.  Adequate  ventilation  and 
strict  attention  to  the  demands  of  sanitation  are  necessary  hygienic 
requisites  which  must  not  be  overlooked. 

The  furniture  and  appliances  should  be  especially  adapted  to  the 
needs  of  the  worlonan,  and  arranged  to  facilitate  ease  and  celerity  in  his 
manipulations.  Every  article  which  is  used  in  the  laboratory  should 
have  a  place  provided  for  it,  to  which  it  may  be  returned  when  not  in 
service.  Systematic  care  of  the  tools  and  instruments  and  orderliness 
and  cleanliness  in  the  various  mechanical  procedures  should  characterize 
the  laboratory  work. 

The  usual  equipment  of  a  dental  laboratory  consists  in  a  suitable 
work-bench,  carefully  adapted  to  the  purpose  for  which  it  is  to  be  used; 
a  molding  box;  plaster  table  and  sink;  a  swaging  block  and  anvil;  at 
least  two  lathes,  one  designed  especially  for  the  grinding  and  fitting  of 

17 


18  THE  LABORATORY. 

teeth,  the  otlier  for  finishing  and  poHshing  only;  a  mechanical  blowpipe 
table,  supplied  with  gas-burner  on  the  Bunsen  principle,  of  sufficient 
capacity  to  allow  of  the  soldering  of  full  dentures. 

In  addition  to  these  permanent  articles  of  laboratory  furniture  it  will 
be  necessary  to  provide  a  suitable  furnace  for  the  melting  of  zinc,  lead, 
and  alloys  commonly  used  in  making  dies  and  counter-dies,  and  also 
another  and  difi'erent  one  to  be  used  for  the  occasional  melting  of  gold 
and  silver  and  in  the  formation  of  alloys  to  be  used  as  solders.  Besides 
these  a  vulcanizer  to  be  used  in  vulcanizing  dental  rubber,  porcelain 
furnaces  for  the  baking  of  inlays,  crowns,  and  continuous-gum  dentures, 
and  for  staining  teeth,  and  a  gold  casting  a])])aratus  for  casting  molten 
gold  are  necessary  adjuncts  to  a  fully  ecjuij)])ed  laboratory. 

The  accessories  of  soldering,  molding  rings  and  flasks,  ingot  molds, 
rolling  mills,  draw-plates,  pickling  solutions,  with  the  most  suitable 
vessels  for  holding  the  same,  grinding  and  polishing  materials,  fluxes, 
varnishes,  adhesive  wax,  and  bench  tools,  all  necessarily  form  part  of 
the  equipment  of  the  dental  laboratory,  and  will  each  be  described 
in  this  chapter  or  in  the  chapter  devoted  to  that  special  subject. 

The  Work-bench. — The  work-bench  should  be  constructed  of  cherry, 
ash,  or  well-seasoned  oak;  it  should  be  provided  with  not  less  than  two 
sets  of  drawers,  one  to  contain  the  ordinary  bench  tools,  being  ar- 
ranged in  a  tier  at  the  right  hand  side;  the  other  directly  in  front  of  the 
workman  and  over  his  lap,  and  intended  for  the  storing  of  the  materials 
he  is  using  and  the  filings  and  scraps  from  the  same.  Such  a  bench  will 
presently  be  described. 

The  height  of  the  work-bench  should  be  about  34  inches,  which  places 
the  work  the  proper  distance  from  the  eyes  when  the  workman  is  seated 
upon  a  stool  of  usual  height  (about  18  inches).  Jewelers'  benches  which 
have  been  used  for  dental  work  are  too  high,  as  they  have  been  designed 
for  operations,  which  necessitate  closer  vision.  It  may  be  said  that  the 
stool  upon  which  the  operator  sits,  his  own  physique,  and  the  height  of 
the  bench  should  be  so  correlated  that  the  work  is  not  so  close  to  the 
workman's  eyes  as  to  put  a  continuous  strain  upon  the  accommoda- 
tion, and  yet  is  clear  enough  for  comfortable  vision  without  his  bending 
over.  The  bench  should  be  located  so  that  the  workman  faces  the  light, 
and  for  this  reason  it  should  be  given  the  preference  in  position  over  any 
other  laboratory  furniture.  The  length,  when  designee!  for  the  conveni- 
ence of  two  workmen,  should  be  about  .')  feet  ()  inches;  the  width  may  be 
24  inches.  The  top  should  be  at  least  1  inch  in  thickness,  and  immedi- 
ately over  the  tool  drawers  should  be  arranged  a  rest  for  convenience  in 
filing  and  finishing.  This  rest  is  usually  made  of  the  same  hard  wood 
as  the  top  of  the  bench,  2  inches  wide  and  about  3  inches  long,  tapering 
from  IJ  inches  in  thickness  where  it  is  mortised  into  die  table  to  \ 
inch  at  its  extremity.  It  is  desirable  that  the  bench  l)e  firm  and  solid  to 
withstand  any  force  exerted  upon  it  in  use,  and  it  is  advisable  in  some 
cases  to  have  it  fixed  to  the  wall,  especially  if  it  is  to  be  used  as  a  support 
for  the  vise  in  drawing  wire.  Where  it  is  possible,  se})arate  benches 
should  be  provided  for  the  several  classes  of  lal)oratory  operations.  The 
tools  and  materials  for  each  kind  of  work  are  then  kept  together,  and  a 
mixing  of  the  scraps  and  debris  of  the  various  operations  is  prevented. 


THE   WORK-BENCH.  19 

It  is  particularly  important  that  a  bench  or  portion  of  the  bench  be  kept 
solely  for  work  with  the  precious  metals. 

A  very  convenient  and  elaborate  work-bench  of  good  design  is  shown 
in  Figs.  1  and  2.  It  is  especially  adapted  to  meet  the  wants  of  those 
who  do  crowm  and  bridge-work.  It  is  provided  with  a  rolling  top,  which 
automatically  locks  the  drawers  when  closed  and  yet  does  not  obstruct 
the  light  when  open.  It  is  provided  with  a  foot-bellows,  and  drawers  for 
gold  solder,  phite,  wire,  files,  scrapers,  corundum  wheels,  pliers,  cutters, 
benders,  etc.;  some  of  the  most  complete  being  shown  by  Figs.  3,  4,  5, 
and  6.  This  bench  is  a  highly  finished  piece  of  cabinet  work,  and 
would  be  suitable  for  the  operating  room  for  such  work  as  it  is  desired 
to  do  while  the  patient  is  in  the  chair. 

Three  benches  are  shown  in  Figs.  7,  8,  and  9  for  vulcanite  and  gold 
and  general  plaster  and  sand  work,  respectively.  The  higher  part  of  Fig. 
7  is  surmounted  by  a  marble  slab,  16^  X  14^  inches,  for  the  accommoda- 
tion of  the  vulcanizer.  Beneath  the  slab  are  two  drawers  3  inches  deep, 
for  flaslvs,  wrenches,  and  tools  used  about  the  vulcanizer.  The  third 
drawer  contains  a  series  of  shallow  compartments  for  the  reception  of 
scrapers,  etc.  The  fourth  drawer  is  partially  divided  by  grooved  com- 
partments similar  to  drawer  No.  3,  and  is  intended  for  files,  etc. 
Drawers  five  and  six  are  for  hammers,  horn  mallets,  and  other  large 
tools,  and  for  rubber,  w^ax,  and  other  supplies.  The  cupboard  contains 
a  shelf,  and  \\dll  be  found  convenient. 

Adjacent  to  the  series  of  drawers  described  above,  and  under  the  right- 
hand  end  of  the  lower  top,  is  a  cupboard  designed  for  the  tooth  stock. 
This  cupboard  contains  a  removable  case  diAaded  horizontally  through 
the  centre  and  of  a  wddth  to  receive  the  boxes  in  which  teeth  are  sold, 
the  ends  of  the  boxes  projecting  beyond  the  case  to  allow  an  easy  with- 
drawal. For  convenience  the  contents  of  each  box  may  be  marked  upon 
its  end,  and  the  inner  case  and  its  contents  may  be  removed  and  placed 
in  a  safe. 

At  the  left-hand  end  of  the  bench  are  two  drawers,  one  containing  a 
rack  into  the  holes  of  which  the  mandrels  of  the  lathe  wdll  drop,  allowing 
the  grinding  wheels  to  rest  upon  the  surface  of  the  rack  and  keeping 
the  wheels  separated  and  in  place.  To  the  right  of  this  drawer  is 
another  drawer  of  the  same  size  for  brush  wheels,  felt  wheels,  and  cones. 
BetW'Cen  these  last  two  drawers  runs  the  belt  of  the  lathe. 

The  lower  top  of  the  bench  is  of  hard  maple,  finished  smooth,  and  a 
4-inch  rail  extends  along  the  back  and  end. 

The  fihng  block  is  placed  in  such  a  location  that  the  workman,  when 
using  it,  is  within  easy  reach  of  his  tool  draw^ers. 

The  top  of  the  bench  represented  by  Fig.  8  is  a  marble  slab  16  x  34 
inches,  and  a  rail  extends  around  the  two  ends  and  back.  Under  the 
right-hand  end  is  a  slide,  and  beneath  this  slide  is  a  drawer  arranged 
w^th  shallow  compartments,  concave  in  shape,  for  files,  etc.,  each 
compartment  being  intended  for  a  single  instrument.^ 

Beneath  this  drawer  are  two  drawers  containing  divisions  of  suitable 
size  to  hold  the  various  plate-cutters,  benders,  punches,  shears,  pliers,  etc. 

Drawers  four  and  five  are  for  bulky  tools  and  supplies. 

The  lower  compartment  contams  the  foot  bellows  fixed  permanently 


Work  bench,  closed. 


20 


THE   WORKBENCH. 


21 


in  place,  the  treadle  only  of  which  projects  in  front  of  the  bench.  The 
bellows  is  connected  with  a  metal  pipe  in  the  rear  right-hand  corner  of 
the  bendi,  and  this  pipe  extends  upward  behind  the  drawers  and  through 


Fig.  3 


Fig.  4 


Drawer  for  gold,  solder,  plate,  and  ware,  with 
bora.K  block,  etc. 


Drawer  for  files  and  scrapers. 


Fig.  5 


Fig.  6 


Drawer  for  mounted  grinding  wheels. 


Drawer  for  pliers,  cutters,  benders,  etc. 


the  marble  slab,  and  is  surmounted  by  a  neat  polished  brass  casting  with 
a  horizontal  nozzle  to  which  the  blowpipe  tubing  may  be  attached.  This 
arrangement  of  the  bellows  overcomes  the  disadvantages  of  having  the 
bellows  continually  under  foot,  and  the  tubing  lying  across  the  bench 
and  hanging  down  in  front.  The  bellows  is  made  specially  for  this 
bench  and  is  shipped  connected  and  ready  for  use,  but  the  ordinary 
bellows  can  be  adapted  to  the  compartment  and  easily  connected  to  the 
metal  pipe. 

If  the  compressed  air  tank  be  used  instead  of  the  bellows,  the  lower 
compartment  may.  be  utilized  as  a  dravrer  by  withdrawing  and  reversing 
it,  the  other  end  of  the  drawer  being  finished  and  furnished  with  .a  drawer 
pull.  The  front  end  then  becomes  the  rear  end  and  the  opening  is  closed 
by  a  slide  furnished  with  all  benches. 

Under  a  filing  block,  which  is  furnished  with  the  bench,  near  the  left- 
hand  end  of  the  bench,  is  a  drawer  arranged  with  concaved  blocks  cut  out 
of  the  solid  wood.  One  of  these  concavities  is  elliptical  in  shape  for  gold 
plate,  wire,  etc.,  and  five  are  circular  in  shape  for  different  grades  of  gold 
solder  or  for  other  purposes.  The  drawer  also  contains  a  slightly  con- 
caved borax  block  or  marble  |  inch  thick,  and  a  grooved  block  from 
which  brushes  and  small  instruments  may  be  readily  taken.  This 
drawer  can  only  be  opened  by  one  who  knows  the  location  of  a  secret 
lock.  Below  the  gold  drawer  is  a  slide  of  zinc  in  a  wooden  frame  for 
catching  gold  filings.  This  slide  gradually  slopes  downward  to  a  cen- 
tral recess,  which  has  a  screw  cap  removable  from  below. 

The  top  of  the  bench  represented  by  Fig.  9  is  a  marble  slab  19^^  X  24 


oo 


THE  LABORATORY. 


Fio.  7 


Work  bench  for  vulcanite  work. 
Fig.  8 


Work  bench  for  gold  work. 


inches,  and  overhangs  the  front,  so  that  the  dentist  may  stand  close 
without  touching  the  lower  part.  Around  the  sides  and  back  is  a  rail, 
and  at  the  back  of  the  marble  slab  is  an  opening  If  X  6  inches,  which 


ACCESSORIES  OF  THE   WORK-BENCH. 


23 


enters  a  metal  cliiite  for  carrying  away  waste  plaster,  etc.,  through  the 
bench,  back  of  the  drawers,  to  a  galvanized  iron  receptacle  beneath. 
This  receptacle  rests  upon  a  shelf,  and  can  be  drawn  forward  by  its  two 
handles  and  removed  when  its  contents  are  to  be  disposed  of.  The  left 
upper  drawer  is  for  rubber  bowls  and  articulators. 

i3eneath  the  upper  drawer  is  a  shallower  one  arranged  with  compart- 
ments, concave  in  shape,  for  spatulas,  plaster  knives,  etc.,  the  arrange- 
ment of  the  compartments  being  such  that  the  various  tools  remain 
where  placed.  At  the  right  of  the  two  drawers  already  mentioned  is  a 
tight  drawer  lined  with  zinc,  for  sand,  molding  rings,  ladles,  and  all 
appliances  used  in  casting.     The  long  drawer  above  the  two  lower 


Fig.  9 


Work-bench  for  plaster  and  sand  work. 

compartments  contains  divisions  for  eighteen  impression  trays.  The 
two  lower  compartments  are  V  shaped  and  hinged  at  the  lower  point. 
One  is  for  impression  plaster  and  the  other  for  cast  plaster.  The 
centre  of  gravity  of  these  drawers  is  such  that  they  remain  in  either  an 
open  or  closed  position  as  placed.  These  benches  have  not  been  im- 
proved upon  for  convenience.  In  laboratories,  w'here  space  must  be 
economized,  one  of  the  combination  benches  designed  for  the  several 
classes  of  work  may  be  desirable.  Figs.  10,  11,  and  12  show  two 
recent  approved  patterns. 

Accessories  of  the  Work-bencli. — A  good  vise  is  an  important  adjunct 
to  the  work-bench,  and  is  indispensable  w^hen  the  draw-plate  is  used  for 
reducing  the  size  of  gold,  platinum,  or  silver  wire. 


24 


TJiE  LABORATORY. 


Rubber  slabs  h  incli  in  thickiu-ss  l)y  (i  inclu's  s(|uaro  aiford  excel- 
lent rests,  not  only  lor  the  protection  of  the  to])  ot"  the  beneh  from 
injury  by  contact  with  dies  and  counter-dies  in  the  j)reliniinary  stage  of 
plate-making,  but  also  as  pliant  and  elastic  rests  for  the  metallic  or 
rubber  denture  durin<r  filinir  and  finishintr. 


Combination  bench  for  general  laboratory  work. 


Molding  Bench. — This  article  of  laboratory  furniture,  shown  by  Fig.  13, 
demands  special  attention  in  its  construction,  otherwise  it  will  prove  a 
constant  annoyan(-e,  as  no  ordinary  wooden  box  will  remain  tight  enough 


Fio.  12 


A  B 

Combination  bencli  for  general  laboratory-  work:    .4,  Closed;    B,  open. 

to  prevent  the  molding  material  from  falling  through  its  seams  upon  the 
floor.  The  diagram  shows  the  general  design  of  one  which  has  been 
found  practical  and  convenient. 

"The  box  is  divided  into  two  compartments  and  is  lined  with  .sheet 


MOLDING  BENCH. 


'25 


copper.  The  eonipartnient  on  tlie  right  hand  ((')  is  for  the  (hunj) 
niokhng  sand  ready  for  use.  The  left-hand  compartment  contains 
a  fixed  block  (A)  ])laccd  in  the  front  right-hand  corner:  the  face  of 
this  block  is  about  (5  inches  scjuare  and  about  1  inch  below  the  edge 
of  the  box.  On  this  the  molding  is  done.  The  remaining  portion 
of  this  compartment  is  covered  with  a  movable  cast-iron  tray  (B)  on 
which  molds  are  set  when  ready  to  pour.  After  the  sand  has  been 
used,  it  is  passed  to  the  box  beneath  through  a  square  hole  at  the 
right-hand  corner  of  the  tray.  By  this  arrangement  the  wet  and 
dry  sand  are  kept  separate,  and  the  tray  is  not  encumbered  with  the 
sand  that  has  been  used.      Underneath  the  box  is  a  drawer  in  which 


Fig.  13 


Molding  bench:  A,  Molding  block;  B,  iron,  tray;  C,  compartment  for  molding  material  ready  for  use. 

(Trueman.) 


the  tools  used  in  molding  are  kept,  and  underneath  this,  forming  a  stand 
for  the  box,  are  four  strong  shelves  covered  with  sheet  zinc  to  prevent 
wear,  on  which  the  flasks,  new  and  old  dies,  zinc  and  lead,  etc.,  are  kept." 
Wlien,  for  any  reason,  the  laboratory  is  not  to  contain  a  molding 
bench,  a  very  satisfactory  substitute  maybe  found  in  a  tray,  18  X  24  inches, 
with  a  2-inch  ledge  around  one  long  and  the  two  short  sides,  covered 
with  sheet  copper  or  zinc.  This  may  be  placed  upon  the  work-bench 
when  needed  and  the  molding  operations  performed  on  it,  and,  as  it  takes 
up  little  room,  may  be  conveniently  stored  when  not  in  use.  In  conjunc- 
tion with  this  must  be  provided  an  earthen  crock  to  store  the  sand  in,  or 
a  tin  container,  such  as  is  sold  with  the  preparations  of  marble  dust  used 
for  molding.  The  "molding  blocks"  presently  to  be  described  v\ull  be 
found  useful  adjuncts. 


26 


THE  LABORATORY. 


Accessories  of  tlie  Molding  Box. — Accessories  of  the  molding  box  con- 
sist of  the  various  sizes  of  the  Bailey  molding  flask,  which,  with  the 
method  of  using  them,  will  be  described  under  the  head  of  Dies  and 
Counter-dies;  one  Ilawes  flask  (see  Chapter  IX.). 

It  is  essential  that  all  molding  operations  should  be  performed  upon 
perfectly  level  surfaces,  and  for  this  puipose  two  or  three  "molding 
l)l(M?ks"  of  seasoned  pine,  8  inches  scjuare  by  2  inches  thick,  will  be 
found  convenient  aids.  In  order  to  avoid  luiupiness  and  to  secure 
uniformity  of  condition  in  the  sand  when  moistening  it  preparatory  to 
molding,  a  sieve  of  not  less  than  12  inches  in  diameter,  with  meshes  of 
a  minimum  size  of  yV  inch,  will  be  found  of  value.  The  sieve  should 
be  formed  of  brass  or  copper  wire,  as  an  ordinary  iron-wire  sieve  will 
soon  become  useless  from  oxidation,  which  is  greatly  assisted  by  contact 
with  the  wet  molding  sand.  A  painter's  brush,  1|  inches  in  diameter 
by  2  inches  in  length,  will  be  found  useful  and  convenient  for  the  purpose 
of  removing  adherent  particles  of  molding  sand  from  the  surface  and 
interstices  of  the  plaster  model  each  time  it  is  drawn  from  the  sand 

Fig.  14 


Fig.  15 


Swaging  block. 

matrix :  also,  a  small  molding  trowel  for  use  in  manipulating  the  sand, 
and  a  gla.ss  tube  to  blow  out  sand  which  has  accidentally  fallen  into  a 
finished  mold. 

Anvil  and  Swaging  Block. — As  the  laboratory  is  often  situated  on  an 
upper  floor,  the  use  of  the  hammer  in  swaging  plates  may  be  the  cause 
of  much  annoyance  from  noise  and  vibration.  This,  however,  can 
be  entirely  avoided  by  interpo.sing  rubber  between  the  block  and  the 
floor  upon  which  it  rests.  Fig.  14,  A,  shows  the  block  of  pine  or  poplar 
wood,  Ih  inches  square  by  23^  inches  high.  B  and  C  represent  a  sheet 
of  rubber  8^  inches  square  by  H  inches  thick,  securely  fastened  to  the 
lower  end  of  the  block  by  screws.  This  V)lock  fits  into  a  box  made  of  H- 
inch  pine  boards,  broader  below  than  al)Ove  ( Fig.  1 5,  L>),  furni.shed  with  a 
loose  bottom,  made  of  2-inch  seasoned  oak  or  ash,  and  provided  with 
four  pieces  of  solid  rubber  cylinder  (Fig.  14,  E)  \\  inches  in  diameter 
by  2  inches  long,  let  into  it  by  holes  of  the  same  dimensions  bored  to  a 
depth  of  IJ  inches.  Two  thicknesses  of  rubber  are  thus  interpo.sed 
between  the  block  upon  which  the  anvils  rests  and  the  floor  of  the  labor- 


n ASTER   TABLE  ASD  SISK. 


27 


atorv,  and  so  much  of  the  sound  due  to  the  percussive  force  of  the 
hammer  is  thereby  deadened  that  scarcely  any  noise  or  vibration  will 
be  observed  by  persons  in  other  parts  of  the  house. 

The  anvil  (Fig.  16),  which  should  weigh  not  less  than  40  pounds, 
may  be  securely  fastened  to  the  block  upon  which  it  rests  by  strong  iron 
staples  (G),  and  the  box  or  outside  covering  of  the  block  reinforced  by 
iron  bands,  as  shown  at  H.  A  swaging  block  so  constructed  may  be 
looked  upon  as  a  permanent  piece  of  laboratory  furniture,  and  one  that 
will  not  be  likely  to  get  out  of  order.  An  anvil  resting  upon  a  bed  of 
sand  contained  in  its  base  of  sheet  galvanized  iron  sold  in  the  supply 
stores  has  proved  very  satisfactory  in  laboratories  where  space  is  a  con- 
sideration. The  sand  takes  up  a  great  deal  of  the  vibration  imparted  to 
the  anvil  in  swaging.  Fig.  17  shows  the  anvil  and  base.  Two  swaging 
hammers  are  required — one,  weighing  about  2  pounds,  is  of  much  use 

Fig.  17 


Fig.  16 


An%'il  mounted  upon  swaging  block. 


Swaging  anvil. 


in  starting  the  plate.  The  heavier  one,  which  should  weigh  5^  or  6 
pounds,  is  used  with  greater  force  after  the  plate  has  been  made  to 
partially  conform  to  the  zinc  die  when  there  is  no  longer  danger  of  its 
pleating  or  folding. 

Plaster  Table  and  Sink. — The  working  of  plaster,  which  forms  so  im- 
portant a  part  of  the  operations  of  the  dental  laboratory,  is  entitled  to  much 
more  care  and  attention  than  it  usually  receives  at  the  hands  of  the  mechan- 
ical dentist.  It  may  be  employed  with  neatness  and  precision,  when  its 
results  become  truly  artistic,  or,  as  is  too  often  the  case,  it  may  be  handled 
in  so  slovenly  and  untidy  a  manner  as  to  greatly  lower  the  standard  of 
results,  and,  unless  kept  carefully  within  the  precincts  assigned  it,  cause 
the  laboratory  to  become  a  most  unattractive  place.  It  is  of  importance, 
therefore,  that  a  suitable  table  be  provided  upon  which  the  casting  and 
subsequent  trimming  of  plaster  casts  and  other  parts  of  the  laboratory 


28  THE  LABORATORY. 

work  ck'pciKling  upon  tlic  ('iii])l()yiii(Mit  of  plaster  may  be  performed. 
The  plaster  table  should  also  be  supplied  with  a  receptacle  for  the  cut- 
tings and  refuse  fragments.  The  table  already  described  on  page  22 
has  proved  of  very  useful  design. 

The  accessories  of  the  plaster  table  consist,  first,  of  two  short,  broad- 
necked  bottles,  for  sandarac  and  shellac  varnish,  two  or  more  flexible 
rubber  plaster  bowls,  the  same  number  of  bone,  ivory,  or  steel  spatulas 
for  mixing,  one  or  more  plaster  knives,  such  as  are  sold  at  the  dental 
depots  for  the  purpose  of  reducing  the  size  of  plaster  casts,  for  flasking 
in  rubber  or  celluloid  work,  and  a  number  of  different  sizes  of  camel's- 
hair  brushes,  which  are  indispensable  in  carrying  the  plaster  into  the 
deeper  parts  when  running  or  casting  impressions  for  partial  dentures, 
and,  indeed,  all  impressions  having  deep  and  more  or  less  inaccess- 
ible points,  which  might  not  be  perfectly  reached  l)y  the  gravitation 
of  the  plaster  unassisted  by  some  such  means  as  is  suggested  l)y  the 
use  of  the  camel's-hair  pencils  or  brushes. 

Two  kinds  of  varnish  are  usually  employed  in  the  ])reparation  of  the 
surfaces  of  impressions  for  running  out  the  casts,  so  as  to  prevent  too 
close  adhesion  of  one  to  the  other.  One  is  transparent  and  dries  upon 
the  plaster  without  color.  The  other  is  of  the  color  of  burnt  sienna,  and 
imparts  a  dark-yellow  stain  to  the  plaster.  The  first  is  made  by  dissolv- 
ing 5  ounces  of  gum  sandarac  in  a  c)uart  of  alcohol.  The  latter  is  formed 
of  gum  shellac  and  alcohol  in  the  same  proportions.  Gum  sandarac  dis- 
solves rather  slow'ly,  and  recjuires  a  good  c|uality  of  alcohol  free  from  a 
very  considerable  percentage  of  water;  otherwise  it  will  have  a  milky 
appearance  and  will  not  afford  a  perfectly  glazed  surface  when  applied 
to  the  plaster  impression.  These  two  varnishes  are  employed  for  totally 
different  purposes.  In  running  out  an  impression  the  object  should  be 
to  obtain  a  perfect  surface  to  the  cast,  one  that  is  free  from  air-bells 
or  roughness  of  any  kind,  as  such  imperfections  will  be  represented  on 
rubber  or  celluloid  dentures  by  multitudes  of  minute  globules  which  are 
highly  irritating  to  the  nmcous  membrane  of  the  mouth.  The  shellac 
varnish  should  be  applied  first,  as  it  penetrates  the  plaster  and  di.scolors 
it  sufficiently  to  serve  as  a  guide  in  removing  imjiressions  from  casts, 
and  thus  prevents  the  workman  from  injuring  the  teeth  t)r  prominent 
parts  of  the  cast.  After  the  shellac  varnish  has  been  allowed  to  dry, 
the  sandarac  should  be  applied  with  a  canuTs-hair  brush  until  the 
surface  is  glazed.  It  should  be  laid  on  of  a  uniform  thickness,  but  not  in 
such  quantity  as  to  fill  up  deep  places  or  to  injure  the  correctness  of  the 
fac-simile  of  the  mouth. 

After  the  last  coat  of  varnish  has  been  allowed  to  dry,  if  the  glazing 
of  the  surface  is  satisfactory,  the  plaster  impression  merely  requires  to  be 
dipped  in  water  to  ensure  saturation  and  to  further  harden  the  varnish, 
when  it  is  ready  for  running  the  cast.  Careful  attention  to  these  details 
will  produce  a  cast  possessing  hardness  of  surface,  and  with  the  glazed 
appearance  which  is  noticed  when  plaster  is  poured  and  allowed  to  set 
upon  glass.  This  result,  however,  cannot  be  obtained  when  oil  or  solu- 
tions of  soap  have  been  used;  such  substances  should  never  be  applied 
to  plaster  impressions,  as  they  do  not  afford  surfaces  sufficiently  smcDth 
or  hard  upon  which  to  form  rubber  or  celluloid  dentures.     To  get  the 


PLASTER   TABLE  AND  SLXE.  29 

best  results  in  the  handling  of  plaster,  the  latter  in  mixing  should  be 
slowly  dropped  into  water  until  it  becomes  saturated  and  settles  to  the 
bottom  of  the  bowl,  so  as  to  expel  the  air.  The  sur])lus  of  water  is  then 
pouretl  ort'  and  the  plaster  well  stirred,  when  it  should  be  earned  to  the 
surface  of  the  impression  and  into  the  deep  parts  with  a  camel's-hair 
brush,  and  the  balance  built  up  with  the  spatula. 

Plaster  of  Paris  is  prepared  from  a  native  calcium  sulphate  known 
as  g}'])sum  (CaSO,  +  2H20).  There  are  other  native  sulphates  of  cal- 
cium: alabaster,  which  is  a  whitish  translucent  mineral;  selenite,  which 
is  transparent;  but  gypsum,  which  occurs  in  opaque  white  masses,  is  the 
common  source  of  plaster  of  Paris.  The  latter  is  obtained  from  g>'psum 
by  a  partial  dehydration,  die  process  removing  one  of  the  molecules  of 
the  water  of  crystallization  and  leaving  plaster  of  Paris  (CaSO^  +  H^O), 
a  substance  which,  when  mixed  with  water,  has  the  property  of  taking 
up  the  other  molecule  of  water  of  crystallization  and  of  crystallizing  with 
the  formation  of  the  original  hydrate  (CaSO^  +  2H20). 

In  making  plaster  of  Paris,  the  g}^sum  is  crushed  into  conveniently 
sized  masses,  is  freed  of  its  impurities,  and  roasted  in  an  oven,  a  kettle, 
or  a  rotating  cylinder  at  a  temperature  not  exceeding  400°  F.  At  212° 
F.  it  begins  to  give  off  some  of  its  combined  water;  at  about  261°  F.  the 
best  plaster  of  Paris  is  made,  and  if  heated  above  .400°  F.  more  than  one 
molecule  of  water  is  driven  off,  and  the  property  of  the  plaster  to  again 
take  up  this  water  is  impaired  or  entirely  destroyed.  After  calcining,  the 
plaster  is  ground  to  various  degrees  of  fineness,  according  to  the  use  to 
which  it  is  to  be  put. 

When  mixed  with  the  correct  proportion  of  water,  plaster  of  Paris 
hardens  by  crystallization,  and  this  hardening  or  setting  is  attended  with 
a  slight  evolution  of  heat  and  a  slight  expansion,  usually  about  -j-g-Q-  of 
its  volume.  Various  factors  affect  the  amount  of  the  expansion,  which  for 
obvious  purposes  of  accuracy  when  used  in  the  dental  laboratory  should  be 
reduced  to  the  minimum.  The  time  occupied  in  setting  varies  with  dif- 
ferent plasters  used  in  dental  work,  and  various  factors  affect  this  time. 
The  relationship  of  these  various  factors  to  both  the  degree  of  expansion 
and  the  time  of  setting  will  be  discussed  in  Chapters  VII.  and  VIII. 

Two  separate  kinds  of  plaster  are  employed  in  the  dental  laboratory, 
one  for  taking  impressions,  and  the  other  for  dental  casts. 

Plaster  w^hen  not  being  used  should  be  kept  covered  to  shield  it 
from  occasional  dampness  of  the  atmosphere  and  to  protect  it  from  water 
and  foreign  substances  which  might  accidentally  fall  into  it.  The  tin 
cans  in  which  plaster  is  furnished  by  the  dental  depots  are  admirably 
suited  to  this  purpose.  The  Ohmer  dental  bin  is  a  more  convenient 
receptacle.  A  closed  tin  container  is  provided  at  the  bottom  with  a  sieve 
actuated  by  a  crank,  by  means  of  which  the  plaster  may  be  slowly  sifted 
into  the  mixing  bowl,  any  large  particles  of  extraneous  matter  being 
restrained  by  the  sieve.  The  Ohmer  bin  is  of  good  design,  but  should  be 
of  stronger  construction.  The  author  has  recently  obtained  flour  bins 
with  a  capacity  of  about  25  quarts  which  are  of  this  same  design,  and,  be- 
ing admirably  constructed,  have  been  extremely  satisfactory. 

A  sink  with  rimning  water  is  practically  a  necessity  for  the  work  in 
plaster,  and  the  plaster  table  should  adjoin  it.     An  ordinary  iron  sink, 


30  THE  LABORATORY. 

such  as  is  used  in  the  kitchen  or  laundry  will  answer  every  purpose. 
Unless  it  is  galvanized,  it  should  be  given  a  coat  of  pitch  to  prevent 
rust.  Precaution  must  be  taken  to  prevent  clogging  of  the  wa^ite  pipe 
with  pieces  of  hardened  plaster  by  providing  guards  and  traps,  and  a 
slatted  wooden  false  bottom  which  may  be  removed  at  will,  mav  be 
fitted  to  the  sink  to  both  stop  the  larger  pieces  of  plaster  and  oft'er  a 
less  hard  and  resistent  surface  to  anything  which  might  be  broken  by 
an  accidental  fall  upon  it. 

Heat  in  the  Laboratory,  This  agent  is  utilized  in  so  many  laboratory 
processes  that  it  is  deemed  wise  to  discuss  its  sources  and  the  principles 
underlying  its  production  before  taking  up  the  methods  which  employ 
it.  In  the  dental  laboratorv-  heat  is  obtained  either  from  the  combustion 
of  fuel  or  from  electric  energy,  the  former  being  its  commoner  source. 
Solid  fuel,  as  coal  or  coke,  is  no  longer  in  use,  having  been  succeeded 
almost  entirely  by  either  liquid  or  gaseous  fuel.  Alcohol,  gasoline,  and 
kerosene  are  the  liquids  used  for  this  purpose;  the  gas  is  commonly  either 
ordinary  illuminating  gas  or  natural  gas  in  those  regions  in  which  it  is 
available.  These  all  owe  their  inflammability  to  the  fact  that  they  are 
hydrocarbons,  combustion  of  which  takes  place  when  they  are  heated 
in  air.  One  of  the  phenomena  of  combustion  is  the  production  of  flame, 
which  is  simply  burning  gas. 

The  simplest  flames^  Tvath  which  we  are  acquainted  are  those  of 
hydrogen  and  carbon  monoxide  burning  in  air  or  oxygen.  In  such  as 
these  the  burning  gas  undergoes  no  decomposition.  The  combustion 
consists  of  the  simple  union  of  an  inflammable  gas  with  oxygen: 

H,  +  O  =  HjO.  2C0  +  Oj  =  2C0,. 

The  flame  of  either  of  these  gases  burning  from  the  end  of  a  tube 
appears  as  a  burning  cone,  which  upon  investigation  is  found  to  be 
hollow,  the  combustion  only  taking  place  on  the  surface  of  the  cone 
where  the  inflammable  gas  is  mixed  by  diffusion  with  the  air. 

Substances  which  undergo  decomposition  and  yield  more  than  one 
product  of  combustion  present  a  more  complex  flame  structure.  The 
flames  of  hydrocarbons  commonly  employed  for  illuminating  purposes, 
such  as  the  candle,  illuminating  gas,  and  oil,  are  practically  identical 
in  points  of  construction  and  a  description  of  one  will  suffice  for  all. 

The  Candle  Flame. — On  approaching  the  wick  with  the  flame  of  a 
match,  the  wax  (or  other  hydrocarbon  of  which  the  candle  may  be  made) 
melts,  is  drawn  up  in  the  fibres  of  the  wick  by  capillary  attraction  and 
there  converted  by  the  heat  into  gaseous  hydrocarbons,  which  ignite, 
and  in  their  chemical  union  with  the  oxygen  of  the  air  produce  the 
flame.  In  such  flames,  as  in  the  simpler  ones  already  referred  to,  there 
is  first,  about  the  wick  or  burner,  the  dark  cone.  A,  of  heated  unburned 
gases.  Above  and  about  the  apex  of  this  cone  is  a  second  cone,  B, 
which  in  comparison  with  the  rest  of  the  flame,  seems  nearly  opaque, 
and  which  emits  a  bright-yellow  light.  At  the  base  of  the  flame  there 
is  a  small  cal^TC-like  region,  C,  which  appears  bright  blue  in  color  and 

1  Manuscript  on  the  flame  furnished  by  J.  D.  Hodgen. 


THE  REDUCING  FLAME. 


31 


IS  non-lummous. 


Fig.  18 


Then  enveloping  the  entire  flame  there  is  a  faintly 
luminous,  hardly  perceptible,  bluish-purple  mantle,  D  (Fig.  18). 

llie  dark  cone,  A,  as  has  been  explained,  consists  of  unburned  gases 
and  in  reality  is  not  a  part  of  the  flame.  However,  chemical 
changes  are  taking  place  therein,  owing  to  the  heat  from  the 
sheath  of  combustion  surrounding  it. 

Cone  B  is  ordinarily  spoken  of  as  the  luminous  cone.  It 
has  been  concluded  probable  that  the  luminosity  in  flame 
is  due  to:  (1)  the  presence  of  solid  matter,  (2)  the  density 
of  the  flame  gases,  and  (3)  the  temperature  of  the  flame. 

The  blue  region,  C,  may  be  regarded  as  being  largely  made 
up  of  the  combustion  of  carbon  monoxide. 

The  faintly  luminous  mantle,  D,  is  probably  a  zone  of 
complete  combustion,  in  which  those  substances  which  have 
been  incompletely  oxidized  in  the  other  portions  of  the  flame, 
chiefly  hydrogen  and  carbon  monoxide,  are  finally  converted 
into  water  and  carbon  dioxide. 

The  Bmisen  and  Blowpipe  Flame.  AMien  a  certain  amount 
of  air  is  mixed  with  coal  gas  or  any  other  hydrocarbon  gas 
before  combustion,  the  gas  burns  with  a  pale-blue,  non-luminous, 
smokeless  flame,  which  has  a  three-cone  structure  (Fig.  19). 

Cone  A  contains  the  mixture  of  combustible  gases  and  air  (oxj'gen). 
In  the  Bunsen  burner  the  air  is  drawn  in  through  the  openings  near  the 
base  of  the  metal  tube.  The  mouth  blowpipe  conveys 
a  blast  of  air  into  the  centre  of  the  flame.  In  the  com- 
pound blowpipe  flame  the  blast  of  air  (ox}^gen)  is  injected 
into  the  combustible  gases  from  the  lungs  of  the  operator 
or  by  some  mechanical  means,  such  as  a  bellows,  through  a 
concentered  tube,  D,  while  the  gas  is  conveyed  by  the 
outer  and  larger  tube,  E  (Fig.  20). 

The  Reducing  Flame. — The  inner  cone,  B,  presents  the 
gas  burning  with  a  pale-blue  flame,  rendered  so  by  the  pre- 
sence of  oxygen  in  the  gas.  If  an  oxidized  piece  of  copper 
be  placed  in  a  Bunsen  or  blowpipe  flame  in  the  position  of 


Candle  flame 


Fig.  19 


ML 


Fig.  20 


Blowpipe  flame. 

the  line  marked  B'  B' ,  it  will  be  noticed  that  the  metallic 
sheet  brightens  in  the  area  covered  by  the  flame.  This  is 
accounted  for  by  the  fact  that  this  region  of  the  flame 
contains  highly  heated  but  unburnt  hydrogen  or  hydro- 
carbons, which  have  the  power  to  abstract  and  then  combine  with  the 
oxygen  of  the  copper  oxide,  thus  freeing  or  reducing  the  copper;  hence, 
this  region  is  known  as  the  deoxidizing  or  reducing  flame. 


Bunsen  flame 


32  THE  LABORATORY. 

This  is  the  flame  used  for  soldering,  ixs  it  reduces  any  oxides  that  ma) 
be  on  the  solder,  or  parts  to  he  soldered,  and,  also  cutting  off  the  oxygen 
of  the  air  from  contact  with  the  heated  metals,  it  prevents  any  reoxid- 
ation  of  them. 

The  Oxidizing  Flame. — The  outer  cone,  C,  presents  a  pale-hlue  or 
purple  color  and  is  tlic  zone  of  complete  combustion.  Gases  which  have 
escaped  combustion  in  the  inner  cone  are  oxidized  in  the  outer  one  by 
the  ample  supply  of  oxygen  in  the  atmosphere  surrounding  it. 

A  bright  piece  of  copper  held  in  the  position  of  the  line  C  C"  will  be 
quickly  darkened  by  the  formation  of  copper  oxide  upon  its  surface. 
This  is  accounted  for  by  the  fact  that  the  copper  becomes  heated,  and, 
being  unprotected,  is  unable  to  resist  the  affinity  of  the  oxygen  in  the  air 
surrounding  it,  and  is  therefore  oxidized.  Hence,  the  term  oxidizinc/famc. 

Any  attempt  at  soldering  with  this  flame  results  in  oxidation  of  the 
base  metals  of  the  solder  and  parts  to  be  soldered,  so  that  adcHtional 
fluxing  will  be  necessary  before  the  solder  can  flow.  Continued  misuse 
of  the  flame  may  so  greatly  raise  the  carat  of  the  solder,  by  oxidizing  out 
the  base  metals,  as  to  make  its  fusing  point  dangerously  high,  or  the 
presence  of  the  oxides  mixed  with  the  solder  may  make  its  flowing 
impossible. 

Because  of  the  chemical  nature  of  combustion,  it  is  evident  that  the 
proportion  between  the  air  and  the  gas  must  be  definite  and  fixed  to 
obtain  the  highest  heat,  and  this  must  be  regulated  when  the  blowpipe 
is  in  use.  If  too  little  air  is  supplied,  imperfect  combustion  takes  place 
and  the  full  degree  of  heat  is  not  developed.  On  the  other  hand,  the 
luminosity  of  the  flame  is  increased,  the  heat  being  inversely  related 
to  this.  If  too  much  air  is  forced  in,  the  temperature  of  the  flame  must 
necessarily  be  reduced  by  the  current  of  cool  and  uncombined  air. 

The  various  heat-producing  appliances  which  burn  gas  operate  under 
the  principles  above  outlined.  They  will  be  described  in  the  portions 
of  this  chapter  which  treat  of  their  use.  Gasoline  and  alcohol  apfjliances 
will  also  be  discussed  later. 

One  of  the  commonest  uses  for  heat  in  the  laboratory  is  in  the  melting 
of  metals. 

Fig.  21  shows  a  form  of  Bunsen  burner  that  has  found  favor  for  general 
laboratory  uses.  Greater  heat  may  be  obtained  by  using  a  larger  burner. 
Recentlv  an  improvement  on  the  Bunsen  principle  has  been  utilized  by 
Dr.  Meker  of  Paris  in  the  construction  of  the  Meker  l)urner.  In  this 
the  air  and  gas  are  more  thoroughly  mixed  in  the  tube,  the  larger  open- 
ings at  the  base  admitting  more  air,  and  a  wire  gauze  at  the  mouth  of 
the  tube  prevents  back  firing.  This  burner,  shown  in  Fig.  22,  has  greater 
heat-producing  capacity  than  a  Bunsen  burner  of  equal  size,  and  the 
flame  is  almost  uniform  in  its  heat. 

Modes  of  Melting  Metals. — The  means  employed  for  this  purpose 
will  depend  upon  the  character  of  the  metal  or  alloy  to  be  fused.'  The 
fusing  of  such  alloys  as  are  used  for  dies  and  counter-dies  in  crown 
and  bridge-work,  which  melt  at  temperatures  ranging  from  158°  F.  to 
2.36°  F. — and  there  are  a  large  number  of  these  alloys  now  in  use — 
may  be  accomplished  by  simply  placing  a  sample  of  any  one  of  them  in 


MODES  OF  MELTING  METALS. 


33 


a  snuill  iron  ladle  provided  with  a  suitable  handle,  or  in  a  copper  ladle 
recently  designed  for  the  purpose  (Fig.  23),  and  holding  it  over  a  Bunsen 
Hume  or  die  flame  of  an  alcohol  or  oil  lamp. 


Fig.  21. 


Fig.  22 


Bunsen  burner  for  laboratory  use. 


Meker  burner. 


Metals  and  alloys  used  in  the  formation  of  dies  and  counter-dies 
melting  in  an  iron  ladle  or  at  below  red  heat  may  be  fused  in  an  ordinary 


Fig.  23 


Ladle  for  fusible  metal. 


Fig.  24 


Fletcher's  furnace. 


Fig.  25 


Burner  for  furnace. 


stove  or  furnace,  or,  where  gas  is  available,  in  one  of  the  furnaces  devised 
by  INIr.  Fletcher,  of  Warrington,  England.     Fig.  24  ^hows  a  furnace  of 
3 


34 


THE  LAIiORATORV 


his  (k'siirii  for  lufltiiii,'  /.iiic,  lead,  and  otht-r  nu-tals  for  (lies  and  counter- 
dies,  which,  it  is  l)clicvcd.  is  unexcelled  by  any  other  yet  made. 


.Milling;  liidU'  and  handle. 


It  works  c(|ually  well  with  any  gas  suj)j)]y  available;  the  s])eed  of 
working  is,  however,  proportionate  to  the  sup])ly  of  gas.  The  burner 
can  be  removed  from  the  casing  and  used  for  other  purposes  if  desired. 
The  cast-iron  ladle  and  handle  are  .shown  in  Fig.  20. 


Fid.  27 


Fig.  28 


Fig  2fl 


Carbon  Mipport. 


It  should  be  remembered  that  zinc  will,  under  favorable  conditions, 
unite  with  iron,  and  it  frecpiently  attacks  the  cast-iron  ladle  in  which  it 
is  melted,  and  may  penetrate  the  side  and  escape  into  the  fire.     Accidents 


MODES  OF  MET/riNC,    MKTAL!^. 


35 


of  this  kind  are  more  likely  to  occur  when  the  ladle  is  new,  and  inay  he 
avoided  by  coating  the  inside  with  whiting  previous  to  the  first  nielting. 
This  coating  should  he  renewed  until  a  protecting  covering  of  oxide  of 
iron  has  been  formed  after  repeated  use  of  the  pot. 

Small  ([uantities  of  gold  or  silver  may  be  melted  by  means  of  the 
ordinary  blowpipe  upon  a  su})p()rt  formed  of  charcoal!  A  good  solid 
cylindrical  piece  of  thoroughly  charred  pine  coal  should  be  selected,  and 
divided  into  two  equal  halves  by  a  vertical  cut  with  a  saw,  as  shown  by 
Figs.  27,  28,  29.  Upon  the  end  of  one  half  a  depression  should  be  cut 
for  the  reception  of  the  metal  to  be  melted  {A).  On  the  flat  side  of  the 
other  half,  extending  to  the  end,  the  ingot  mold  should  be  carved,  of  a 
size  and  shape  governed  by  the  requirements  of  the  case  (B).  The  two 
halves  should  then  be  brought  together  and  secured  by  a  piece  of  iron  or 
copper  wire,  when  they  will  be  found  to  practically  combine  the  recjuire^ 
ments  of  a  crucible  and  ingot  mold. 

The  depression  in  which  the  metal  is  to  be  melted  and  the  mold  or 
receptacle  should  be  connected  by  means  of  a  gutter  or  groove.  The 
flame  of  the  blowpipe  is  directed  upon  the  metal,  and  when  thoroughly 
fluid  the  charcoal  is  tilted,  so  that  the  fused  metal  will  run  into  the 
mold  prepared  for  it  in  the  opposite  half  of  the  charcoal.  This  is 
probably  the  simplest  form  of  apparatus  by  which  small  quantities  of 
metal  can  be  melted,  and  is  often  employed  in  the  dental  laboratory  and 
by  jewellers. 

Mr.  Fletcher  has  devised  an  apparatus  embodying  the  same  general 
principles  as  the  one  just  described  for  quickly  obtaining  ingots  of  gold 
and  silver  without  the  use  of  a  furnace  (Fig.  30):  A  representing  a 
crucible  of  molded  carbon,  supported  in  position  by  an  iron  side-plate; 
B,  the  ingot  mold ;  C,  clamp  holding  ingot  mold  and  crucible  in  position ; 

Fig.  30 


Ingot  mold  and  blowpipe. 

D,  cast-iron  stand  upon  which  the  latter  swivels.  The  metal  to  be 
mehed  is  placed  in  the  crucible  {A),  and  the  flame  of  the  blowpipe  is 
directed  upon  it  until  it  is  perfectly  fused.  The  waste  heat  serves  to 
make  the  ingot  mold  hot.     The  whole  is  tilted  over  by  means  of  the 


36 


THE  LABORATORY. 


upright  liandle  at  the  hack  of  the  mold.    A  sound  ingot  may  be  obtained 
by  tlie  use  of  tliis  sinij)Ie  little  aj)|)aratus  in  a  few  minutes. 

Fig.  31  represents  an  improved  form  of  the  ])reeeding  melting  arrange- 
ment. It  differs  in  that  the  two  parts  of  the  ingot  mold  slide  on  each 
other  to  enable  ingots  of  any  width  to  be  cast,  and  the  blowpipe  is  part 
of  the  rocking  stand.  The  bellows  is  connected  to  the  upper  tube  and 
the  gas  to  the  lower  by  the  usual  means  of  india-rubber  tubing. 

Contrivances  of  this  kind  are,  however,  not  applicable  to  melting 
operations  involving  quantities  exceeding  one  ounce.  In  such  cases  it 
is  better  to  employ  a  crucible  and  any  stove  or  furnace  in  which  the 
temperature  can  be  raised  sufficiently.  This  may  be  accomplished  in 
an  ordinary  cooking  stove,  a  blacksmith's  forge,  or  a  small  fire-clay 
furnace  by  the  use  of  anthracite  coal,  coke,  or  charcoal. 

By  far  the  most  convenient,  compact,  and  effective  furnace  for  melting 
from  one  to  ten  ounces  of  gold  which  has  ever  been  used  is  the  crucible 
furnace  (Fig.  32)  invented  by  ^Ir.  Fletcher,  which  can  be  obtained  at 
the  dental  depots.  It  is  perfectly  adapted  to  the  wants  of  the  mechanical 
dentist.  It  is  composed  of  a  substance  resembling  fire-clay,  but  much 
lighter  in  weight,  and  said  to  possess  only  one-tenth   its  conducting 

power  for  heat.     The  furnace  con- 
'  "•  '^^  sists  of  a  simple  pot  for  holding  the 

crucible,  with  a  lid  and  a  blowpipe, 
all  mounted  on  a  suitable  cast-iron 
base.  The  casing  holds  the  heat  so 
perfectly  that  the  most  refractory 
substances  can  be  fused  with  ease 
by  the  use  of  a  common  foot-blower. 
The  power  which  can  be  obtained 
is  far  l)eyond  what  is  refjuired  for 
most  purposes,  and  is  limited  only 
l)y  the  fusibility  of  the  crucible  and 
casing.  The  graphite  crucible  made 
especially  for  the  Fletcher  furnace 
will  hold  about  ten  ounces  of  gold. 
An  ordinary  gas-supply  pipe  of 
yV-inch  or  f-inch  diameter  will 
work  it  efficiently.  The  blast  is 
obtained  l)y  means  of  a  foot-blower 
connected  with  the  blowpipe  by  a  flexil)le  rubber  tube.  It  requires  a 
much  smaller  supply  of  gas  than  any  other  furnace  known :  about  ten 
cubic  feet  per  hour  is  sufficient  for  most  purposes.  A  gasoline  generator 
has  })een  devised  by  which  these  furnaces  can  l)e  satisfactorily  used  when 
ordinary  illuminating  gas  is  not  obtainable.  Fig.  33  shows  the  generator 
attached  to  the  furnace  with  foot-blower  complete. 

In  size  the  furnace  is  but  4  inches  in  diameter  by  3  in  height.  From 
six  to  eight  ounces  of  gold  rec|uire  from  seven  to  twelve  minutes  for 
perfect  fusion,  the  time  depending  on  the  gas  supply  and  the  pressure  of 
air  from  the  blower. 


Fletcher's  blowpijiu  aud  adjustable  ingot  mold. 


MODES  OF  MELTING  METALS. 


37 


In   melting  any  large  amount  of  gold,  particularly  if  the  melting 
operation  is  performed  in  an  ordinary  coal  stove,  there  is  always  danger 


Fig.  32 


Fig.  33 


Crucible  furnace  for  melting  silver  and  gold. 

of  loss  by  the  escape  of  the  precious  metal  through  some  defect  in  the 

bottom  or  sides  of  the  crucible, 

when  its   recovery  from  among 

the  fuel  and  ashes  of  the  stove  is 

almost    impossible;    but    should 

such  an  accident  occur  when  using 

the  Fletcher  furnace  the  complete 

recovery  of  the   gold  and  silver 

would  not  be  attended  with  the 

least  difficulty. 

A  modification  of  the  appara- 
tus has  been  made,  adapting  it 
to  the  use  of  refined  petroleum 
instead  of  gas  as  a  fuel  (Fig.  34), 
Thus  improved,  it  is  said  to  be  in 
no  way  inferior  in  efficiency  to  the 
gas  furnace.  The  burner  of  this 
furnace  is  constructed  upon  the 
principle  of  an  atomizer,  which, 
of  course,  dispenses  with  a  wick; 
it  is  furnished  with  a  device  for 
regulating  the  supply  of  oil,  which 
is  operated  by  the  milled  nut  A^ 
shown  on  the  top  of  the  reservoir 
in  the  cut,  and  for  the  supply  of 
an  annular  jet  of  air,  which  is 
regulated  by  turning  the  sleeve 
(-B).  This  burner  is  so  arranged 
that  in  case  any  obstruction  should 
occur  it  can  be  taken  apart  and 
cleaned  by  separating  the  burner 
from  the  reservoir,  which  is  ac- 
complished by  loosening  the  small 
screws,  drawing  out  the  oil  tube,  taking  off  the  sleeve  B,  and  removing 
the  inside  tube. 


Crucible  furnace  operated  with  i,a&olint. 


.38 


Tin-:  LABORATOHY. 


Tlu'so  furnaces  are  so  constructed  that  tliev  may  be  used  for  either 
gas  or  jH'troleuni,  the  lani|)  l)eiMg  fitted  for  adjustment  in  place  of  the 
gas  burner,  so  that  the  same  apparatus  may  be  used  for  either.  The 
blast  is  obtained  by  means  of  the  foot-blower,  which  is  connected  with 
the  furnace  by  the  India-rubber  tni)ing,  as  seen  in  the  illustration  (Fig. 
34). 

An  injector  gas  furnace  has  also  been  ])erfected  by  Mr.  Fletcher, 
which  seems  to  be  well  adapted  to  the  wants  of  die  dentist  or  metal- 


Vw.  34 


Crucibk'  furnace  using  petroleum. 

lurgist  (Fig.  35),  and  it  is  claimed  that  its  power  and  .speed  of  working 
are  practically  without  limit,  depending  only  upon  the  gas  and  air 
supply. 

With  a  -2-inch  gas  pipe  and  the  small  foot-blower  this  furnace  will 
melt  a  crucible  full  of  cast-iron  .scraps  in  ten  minutes.  The  supply 
of  gas  required  is  exceedingly  small.  Allowing  five  cubic  feet  of  gas 
for  heating  up,  it  consumes  about  four  feet  of  gas  for  every  pound  of 
metal  melted.  It  is  very  sim])le  in  construction,  and  consists  of  two 
parts — an  upper  portion,  which  forms  the  cover,  and  a  lower  part,  which 
holds  the  crucible  while  in  operation. 


Fig.  35 


luji-ctor  furnace. 


For  melting  platinum  very  high  temperatures  are  required,  and  none 
of  the  appliances  heretofore  dcscriljcd  produce  sufficient  heat  for  the 
purpose.  In  the  soldering  of  continuous-gum  dentures,  in  melting 
platinum  .scraps,  and  in  some  gold  casting  operations,  greater  heat  is 


MODES  OF  MELTING  METALS. 


39 


necessary.  Dr.  J.  Rollo  Knapp  made  use  of  the  principle  of  the  axy- 
hyth'oiijen  blowpipe  in  a  nitrous  oxide  blowpipe  of  his  design,  in  which 
the  ordinary  ilhuninating  gas  furnished  the  hydrogen  element  and  a 
cylinder  of  nitrous  oxide  gas  the  oxygen  element.  The  gases  are  mixed 
in  a  mixing  chamber  and  issue  from  the  blowpipe  ready  to  com- 
bine, producing  an  intense  heat  when  the  proportions  are  properly 
regulated.  LeCron's  blowpipe,  illustrated  in  Chapter  XV.,  is  built  on 
this  principle. 

It  has  been  found,  however,  that  when  a  new  cylinder  is  first  connected 
with  the  apparatus  the  escape  of  the  nitrous  oxide  under  great  pressure 


Lane-Seymour  nitrous  oxide  blowpipe. 


causes  such  a  chilling  of  the  yoke  and  mixing  chamber,  because  of  the 
absorption  of  heat  by  the  nitrous  oxide  in  passing  from  the  liquid  to  the 
gaseous  state,  as  to  interfere  Avith  the  working  of  the  apparatus.  Dr. 
W.  H.  Taggart  has  devised  a  means  of  preventing  this  by  placing  a  very 
small  burner,  connected  to  the  illuminating  gas  supply,  beneath  the 
nitrous  oxide  tube ;  the  latter  is  kept  warm,  condensation  is  prevented,  and 
the  appliance  works  smoothly.    After  the  pressure  in  the  gas  cylinder  has 


40  THE  LABORATORY. 

been  considerably  reduced  in  the  natural  course  of  usiiitr  the  gas,  it  is 
not  necessary  to  keep  the  burner  lighted,  although  better  o])eration  of  the 
blow'j^ipe  is  obtained  by  so  doing.  The  blo\vj)ipe  of  Drs.  Lane  and 
Sevniour,  shown  in  Fig.  36,  is  constructed  upon  this  plan. 

Platinum  scraps  may  be  melted  by  a  method  devised  by  Dr.  L.  E. 
Custer,  of  Dayton,  ( )hio,  which  consists  in  the  use  of  the  intense  heat 
of  the  electric  arc.  The  110-volt  current  is  used.  A  large  quantity  of 
current  is  necessary,  the  fuse  plugs  being  as  large  as  No.  16  or  LS  wire. 
A  resistance  coil  of  eight  pounds  of  Xo.  18  copper  wire  should  be  in 
the  circuit  to  prevent  fusing  the  ])lug  and  to  give  a  large  arc.  The 
platinum  scraps  siu)uld  be  placed  upon  a  block  of  lime  connected  with 
one  wire,  and  the  other  wire  attached  to  a  platinum-pointed  piece  of 
metal  about  f  inch  in  diameter.  This  platinum-tipped  piece  of  metal 
is  brought  in  contact  with  the  scraps,  and  upon  raising  it  a  short  dis- 
tance an  arc  is  formed  directly  upon  the  metal  and  it  is  melted.  The 
arc  can  be  carried  about  at  will  until  the  pieces  are  all  Ijrought  into 
one  mass. 

Crucibles. — The  term  "crucible"  was  originally  applied  to  a  chemist's 
melting-pot,  made  of  earthenware  or  other  material,  and  so-called  from 
the  superstitious  habit  of  the  alchemists  of  marking  such  vessels  with 
the  sign  of  the  cross.  The  term  is  now  generally  understood  as  designat- 
ing vessels  in  which  metals  are  melted  at  high  temperatures. 

A  crucible  should  possess  the  power  of  resisting  high  temperatures 
without  fusing  or  softening.  It  should  also  be  capable  of  retaining 
sufficient  strength  when  hot  to  prevent  its  cnmibling  or  breaking  when 
grasped  with  the  tongs.  Lastly,  it  should  not  crack  either  in  heating 
or  cooling. 

For  the  purpose  of  melting  metals,  crucibles  are  made  of  clay  with 
admixture  of  silica,  burnt  clay,  graphite,  or  other  infusible  material. 
For  use  in  the  dental  laboratory,  graphite  crucibles,  which  can  be  ob- 
tained at  the  dental  depots,  will  be  found  to  answer  every  purpose; 
they  are  thoroughly  reliable  in  strength  and  durability.  They  range  in 
size  fron  2  to  4  inches  high,  and  are  especially  adapted  for  use  in  the 
Fletcher  gas  furnaces. 

When  the  quantity  of  metal  to  be  melted  is  very  small — say,  a  half- 
ounce  of  gold — the  smallest-sized  Hessian  crucible  may  be  used  in  the 
small  Fletcher  apparatus. 

Before  melting  any  considerable  quantity  of  gold  the  crucible  should 
be  tested,  particularly  if  the  melting  operation  is  to  be  performed  in  an 
ordinary  coal  stove,  where  a  defective  crucible  might  be  the  means  of  a 
considerable  loss.  A  small  amount  of  borax  should  be  placed  in  the 
vessel,  which  should  then  be  exposed  to  a  high  temperature.  Should  it 
not  be  perfect,  the  borax  glass  will  run  through  and  glaze  the  surface  on 
the  outside.  If  the  crucible  is  found  to  be  impervious,  it  should  be  so 
inverted  while  yet  hot  that  the  borax  glass  may  cover  the  surface  of  the 
lip  or  groove  out  of  which  the  melted  metal  is  to  be  poured.  This 
facilitates  the  pouring  and  prevents  any  portion  of  the  metal  from 
adhering  to  the  side  of  the  crucible. 


CRUCIBLES. 


41 


Ingot  molds  are  constructed  of  various  substances.  For  the  reception 
of  platinum  melted  by  the  oxyhydrogen  blowpipe  they  are  formed  of 
hme  or  coke;  for  gold  and  silver  they  are  commonly  made  of  cast  iron, 
about  2  inches  square,  and  from  ^  to  -i\  of  an  inch  thick  (Fig.  37), 
with  slightly  concave  inner  surfaces,  as  the  shrinkage  of  the  ingot 
is  greatest  in  the  centre.  Ingot  molds  formed  of  soapstone  are  also 
employed,  but  they  are  not  superior  to  those  made  of  cast  iron. 
Before  pouring  the  ingot  the  mold  should  be  heated,  and  when  made 
to  cast  iron  it  should  be  held  over  a  gas  jet  or  oil  flame  until  its  inner 
surface  is  thoroughly  coated  with  carbon :  this  at  once  prevents  the 
possible  contamination  of    the   gold   by  contact  with   the   iron,  and 


Fig.  37 


Adjustable  ingot  mold. 

the  carbon  layer,  being  a  good  non-conductor,  protects  the  melted  metal 
at  the  moment  of  pouring  from  too  rapid  cooling,  w^hich  otherwise  might 
be  the  cause  of  a  defective  ingot. 

The  ingot  of  gold  or  silver  should  be  as  nearly  rectangular  as  possible 
(Fig.  38),  and  the  operation  of  pouring  the  melted  metal  from  the 
crucible  into  the  ingot  mold  cannot  be  considered  as  successful  unless 
this  result  has  been  attained.  The  experienced  workman  holds  the 
ingot  mold,  which  should  be  provided  with  a  suitable  handle,  with  the 
left  hand,  while  with  the  right  he  removes  the  crucible  from  the  furnace 
and  quickly  carries  it  to  the  ingot  mold,  W'hich  he  slightly  tilts  so  that 
the  melted  metal  may  first  strike  the  side  of  the  mold;  but  he  quickly 
brings  the  mold  to  a  level  before  the  last  of  the  fused  metal  leaves  the 
crucible,  and  thus  avoids  the  danger  of  confining  air  at  the  deepest  part 
of  the  ingot  mold,  which  would  cause  the  ingot  to  assume  an  irregular 
shape  (Fig.  39). 

The  necessity  of  heating  the  ingot  mold  just  before  it  is  to  receive 
the  melted  metal  becomes  apparent  when  we  remember  that  gold  fuses 
at  2012°  F.,  while  the  iron  ingot  mold  at  the  temperature  of  the  atmos- 


42 


THE  LABORATORY 


phere  would  be  about  70°  F.,  aud  when  tlie  amount  of  gold  and  silver 
to  be  melted  is  but  two  or  three  ounces,  the  ingot  mold,  weighing  in 
the  neighborhood  of  twelve  ounces,  would  abstract  so  much  heat  from 


Fig.  38 


Fig.  39 


( 'urivclly  iiiaik'  iiigdt. 


Ingot  iiic'oirectly  inadr  ;   f!iu>(.-(l  Wy 
fonlliiiiiK  !>ir. 


Fig.  40 


lii.i,'(it  iii(<irrectly  iimde  l)ecause  ( 
cold  mold. 


the  metal  as  to  cause  it  to  become  sohd  before  it  reaches  the  lower  part 
of  the  mold,  and  the  result  would  be  an  ingot  triangular  in  shape  (Fig.  40), 
which  could  only  be  at  a  disadvantage  and  lo.ss. 

Rolling  or  laminating  in  the  dental  lal)0- 
ratory  is  accomplislied  by  repeatedly  pass- 
ing the  metallic  ingot  between  cylindrical 
steel  rollers  from  three  to  four  inches  in 
width.  These  are  so  arranged  that  by 
means  of  .screws  they  are  capable  of  being 
brought  closer  together  every  time  the  gold 
is  pa.ssed  through.  (See  Fig.  41.)  The 
proper  degree  of  attenuation  is  determined 
by  the  gauge  plate  (Fig.  42).  After  the 
ingot  has  been  passed  through  the  rolling 
mill  a  number  of  times  it  cannot  be  carried 
through  in  an  opposite  direction  in  order  to  increase  its  width  without 
first  carefully  annealing  it.  This  is  done  by  laying  the  gold  upon  a 
large  piece  of  charcoal  and  directing  the  flame  of  the  blowpipe  upon  it 
until  it  becomes  red  hot.  Failure  to  observe  this  precaution  will  invari- 
ably result  in  serious  damage  to  the  ingot  by  splitting. 

Wire  is  made  by  means  of  the  draw  plate,  which  is  formed  of  an 
oblong  piece  of  hardened  steel  provided  with  a  number  of  gradually 
diminishing  holes  enlarged  on  the  side  the  metal  enters  (Fig.  43). 
The  metal  to  be  drawn  through  may  be  prepared  in  a  cylindrical  shape 
by  melting  and  pouring  into  an  ingot  mold  jn-ovided  with  a  chamber 
for  the  purpose  (some  ingot  molds  are  so  constructed).  The  end  of 
the  rod  should  be  filed  so  as  to  readily  enter  the  draw  plate,  which 
must  be  firmly  screwed  in  a  vice.  The  metal  is  then,  by  means  of  strong 
pliers,  drawn  through  the  different  holes  of  the  draw  plate  consecutively 
until  the  desired  size  is  reache<l.  As  the  work  progresses  the  wire  will 
require  frequent  annealing,  and  to  facilitate  its  passage  through  the 
draw  plate  it  must  be  kept  well  oiled. 


INGOT  MOLDS. 


43 


Fig.  41 


Geared  rolling-mill. 
Fjg  42 


Standard  wire  gauge  plate. 


44 


THE  LABORATORY. 


Half-round,  square,  and  triangular  wires  are  drawn  in  the  same  man- 
ner, except  that  the  holes  in  the  draw  plate  are  made  of  these  respective 
shapes,  instead  of  being  made  round. 


Fig.  43 


20      19      18      17     16      15      14      13      12      11 
•     ••••••••• 

10       9876         54         31 


GARANTIE 


.  Draw  plate. 

Soldering  Apparatus  and  Accessories. — Soldering  must  also,  to  a  certain 
extent,  be  regartled  as  coming  under  the  general  head  of  melting  oper- 
ations, since  it  refers  to  the  union  of  two  or  more  pieces  of  metal  by 
means  of  a  more  fusible  alloy.  The  conditions  of  successful  soldering 
are — (1)  contact  of  the  two  pieces  to  be  united;  (2)  a  clean  metallic 
surface  over  which  the  solder  is  to  flow;  (3)  a  freely  flowing  solder; 
(4)  proper  amount  and  distribution  of  heat. 

Contact  of  the  pieces  to  be  united  is  of  the  greatest  importance.  If, 
for  example,  the  object  to  be  soldered  be  an  artificial  denture,  it  is  indis- 
pensable that  the  backings  be  quite  or  very  nearly  in  contact  with  the 
plate,  and  if  gum  teeth  be  used  that  each  backing  touch  its  neighbor. 
This  is  not  difficult  to  accomplish  if  the  teeth  have  been  carefully  and 
accurately  fitted  to  the  plate  and  to  each  other.  If,  however,  any  defects 
of  this  character  are  found  to  exist  after  the  teeth  have  been  invested, 
they  should  be  remedied  by  filling  such  spaces  or  crevices  Avith  small 
pieces  of  gold  or  silver,  as  the  case  may  be,  thus  rendering  the  continuity 
of  the  parts  complete.  By  the  observance  of  this  precaution  much  of 
the  vexation  in  soldering  experienced  by  beginners  may  be  avoided,  and 
when  the  other  conditions  named  have  been  observed  the  operation 
becomes  exceedingly  simple. 

Solder  runs  freely  by  the  force  of  capillary  attraction  between  two 
closely  fitting  surfaces,  just  as  water  will  be  drawn  against  gravity 
between  two  panes  of  glass  in  close  contact.  In  soldering  artificial 
dentures  which  have  been  carefully  arranged  with  reference  to  contact  of 
all  the  parts  to  be  united,  it  is  quite  possible  to  complete  the  operation  of 
soldering  -without  using  the  blowpipe  at  all,  by  merely  heating  the  whole 
case  to  the  fusing  point  of  the  solder  in  a  charcoal  furnace  with  a  good 
draft.  The  difficulties  of  soldering  are  mainly  due  to  a  violation  of  one 
or  more  of  the  rules  herein  given. 

Cleanliness  should  always  be  strictly  observed  in  soldering  operations. 
The  parts  to  be  united  should  present  bright  and  clean  surfaces. 
Darkening  or  oxidation  -will  always  occur  when  gold  or  silver  the  purity 
of  which  has  been  reduced  by  alloying  is  heated  to  redness.     A  weak 


SOLDERING  APPARATUS  AND  ACCESSORIES.  46 

solution  of  sulphuric  acid  and  water,  slightly  heated,  will  quickly  remove 
discoloration  resulting  from  this  cause,  or  the  borax  employed  as  a  flux 
in  soldering  operations  will  effect  the  same  result  by  dissolving  the  oxide 
which  forms  on  the  surface,  while  it  also  protects  it  from  further  oxidation 
by  excluding  the  atmosphere. 

Where  broad  surfaces  are  to  be  soldered  together — as,  for  instance, 
in  the  construction  of  lower  dentures,  where,  in  order  to  get  sufficient 
thickness,  two  thin  plates  are  swaged  separately  and  then  united  by 
soldering — it  is  even  better,  in  addition  to  the  pickling  process,  to  thor- 
oughly scrape  the  surfaces  to  be  united,  so  as  to  ensure  the  flowing  of  the 
solder  between  the  two  plates.  All  surfaces  to  be  soldered  should  receive 
a  coating  of  borax  before  the  heat  is  applied. 

Borax,  which  is  so  indispensable,  in  soldering  operations,  has  the 
chemical  composition  of  NajB^O^jlOHjO;  it  is  a  pyroborate  of  sodium, 
and  occurs  in  the  waters  of  certain  lakes  in  Thibet,  Persia,  and  Cali- 
fornia. It  crystallizes  in  six-sided  prisms,  which  effloresce  in  dry  air;  it 
dissolves  in  20  parts  of  cold  and  6  of  boiling  water.  On  exposure  to 
heat  the  10  molecules  of  water  of  crystallization  are  expelled;  at  a  higher 
temperature  the  salt  fuses  and  becomes  glass,  in  which  state  it  has  the 
power  of  dissolving  metallic  oxides;  and  it  is  this  quality  which  makes 
it  such  an  admirable  flux  in  soldering  and  melting  operations.  It  must, 
however,  be  kept  scrupulously  clean,  and  especially  free  from  accidental 
admixture  with  plaster  of  Paris.  Recently  fluxes  composed  principally 
of  borax,  prepared  and  used  in  the  form  of  dry  powder,  have  been  intro- 
duced, but  they  are  in  no  respect  superior  to  the  old  way  of  rubbing  up 
the  borax  on  a  piece  of  ground  glass  with  perfectly  clean  water  until  it 
assumes  the  consistence  of  cream,  when  it  is  applied  to  the  surface  to  be 
soldered  with  a  camel's-hair  brush.  A  large  crystal  of  borax  should  be 
selected  for  this  purpose  and  given  several  coats  of  shellac  varnish  to 
prevent  efflorescence.  Powdered  glass  of  borax  is  sometimes  a  useful  and 
convenient  adjunct  when  it  is  necessary  to  apply  more  borax  to  a  hot 
surface,  as  in  that  form  it  may  be  dropped  with  the  fingers  upon  any 
desired  point  of  the  heated  denture  without  danger  to  the  porcelain  teeth. 

Fig.  44  shows  a  convenient  and  compact  arrangement  designed 
by  Dr.  H.  H.  Keith,  of  St.  Louis,  Missouri,  in  which  may  be  kept  the 
borax  crystal,  the  different  grades  of  solder,  tweezers  for  handling 
,  small  pieces  of  solder,  and  camel's-hair  brushes.  It  is  provided  with  a 
ground-glass  plate,  depressed  in  the  centre  (^4),  for  rubbing  the  borax 
with  water  to  the  consistence  suitable  for  application  to  the  metallic 
surfaces  to  be  soldered.  When  not  in  use  it  may  be  closed  with  the  lid 
B,  which  protects  the  borax  from  contamination  with  plaster  or  other 
deleterious  substances.  This  neat  little  accessory  of  the  soldering  table 
is  made  of  walnut  wood  and  is  as  ornamental  as  it  is  useful. 

The  soldering  table  is  an  indispensable  piece  of  laboratory  furniture, 
because  it  enables  the  operator  to  sit  while  soldering,  thus  aft'ording  a 
rest  for  the  right  arm  wdiile  the  hand  guides  the  blowpipe,  and  it  supplies 
a  convenient  place  for  charcoal  "supports"  and  other  soldering  acces- 
sories. Its  top  must  be  of  some  incombustible  material  which  will  not 
crack  under  heat,  such  as  boiler  iron,  which  is  to  be  preferred  to  slate 


46 


THE  LABORATORY. 


or  cement  for  the  reason  named.  A  mecluuiical  blower  and  ])lowpipe 
are  necessary  adjnncts,  altliougli  where  a  supj)ly  of  compressed  air  is 
available  this  may  substitute  the  former,  a  pipe  conveymg  it  to  the  table 
being  conveniently  located  near  that  supplying  the  gas. 

The  mouth  blowpipe  is  an  instrument  which  has  long  been  used  by 
workers  in  metals  for  the  purpose  of  soldering  together  small  pieces 
of  metal  and  for  melting  and  reducing  purposes  generally.  The  ordinary 
form  (Fig.  45,  A)  consists  of  a  conical  brass  tube,  from  200  to  240  mm. 
long,  curved  at  the  narrower  end  to  nearly  a  right  angle,  so  that  the 
flame  may  be  conveniently  directed  upon  the  piece  of  metal  to  be 
soldered  or  melted,  as  the  case  may  be,  which  is  held  upon  some  suitable 
support,  such  as  a  piece  of  charcoal,  coke,  or  pumice-stone.  When  the 
blowpipe  is  used  in  its  simplest  form,  by  the  mouth,  the  large  end  of  the 
instrument  is  held  between  the  lips  and  the  small  end  toward  the  flame. 

Fig  44 


Box  for  borax  and  solder. 


The  blast  should  not  be  sustained  by  the  respiratory  organs,  but,  in 
order  that  an  unbroken  current  may  be  kept  up,  the  mouth  should  be 
filled  with  air,  to  be  forced  through  the  blowpipe  by  the  muscles  of  the 
cheeks.  While  these  are  forcing  the  air  through  the  blowpipe  the  con- 
nection between  the  chest  and  the  cavity  of  the  mouth  should  be  closed 
by  the  palate,  which  thus  performs  the  part  of  a  valve.  The  beginner 
is  liable  to  fall  into  the  error  of  not  closing  the  connection  between  the 
chest  and  the  mouth  at  the  proper  instant,  and  of  obtaining  the  force 
necessary  to  })ropel  the  air  through  the  blowpipe  from  the  lungs.  That 
this  manner  of  using  the  mstrument  may  injure  the  organs  of  respiration 
cannot  for  a  moment  be  doubted,  and  the  operator  should  early  acquire 
the  proper  method  above  described.  To  avoid  tiring  the  muscles  of  the 
lips  by  long-continued  blowing  the  trumpet  mouth-piece  has  been  recom- 
mended, and  is  shown  in  the  annexed  cut  (Fig.  46).  This  is  merely 
pressed  against  the  open  mouth,  and  an  uninterrupted  blast  may  be  kept 
up  for  a  long  time  w^ithout  causing  the  least  fatigue  of  the  orbicularis 
oris,  since,  Avhen  the  trumpet  mouth-piece  is  used,  that  muscle  takes  but 
a  passive  part  in  the  operation.    This  trumpet-piece,  however,  should 


SOLDERING   APPARATUS  AND  ACCESSORIES. 


47 


be  so  curved  as  to  correspond  with  the  shape  of  the  mouth,  otherwise  it 
will  require  to  be  pressed  very  forcibly  against  the  lips  in  order  to  prevent 
the  escape  of  air. 

The  blowpipe  should  be   constructed  of  either 
brass  or  German  silver,  as  these  alloys  are  but  poor       a 
conductors  of  heat.     Silver  is  not  well  suited  for 


Fig.  4.5 


Fig.  46 


Mouth  blowpipe  with  trumpet  mouth-piece. 

the  purpose,  because  it  transmits  temperatures  so 
readily  that  it  soon  becomes  too  hot  for  the  fingers. 
A  long-continued  and  steady  flame  maintained 
by  the  mouth  blowpipe  is  apt  to  cause  disturb- 
ances in  the  flame  from  the  collection  of  moisture 


Fig.  47 


The  mouth  blowpipe  with  condensation  chamber  and 
straight  and  hot  blast  tubes. 

in  the  tube,  which  is  liable  to  be   expelled  by  the 

pressure  of  the  air.    To  avoid  this  a  hollow  chamber 

is  constructed  about  midway  in  the  instrument  (Figs. 

45,  B,  and  47).     The  length  of  the  blowpipe  should  Mouth  blowpipes  (brass), 

be  adapted  to  the  eye  of  the  operator,  so  that  the  object  upon  which 

the  flame  is  directed  may  be  distinctly  seen. 


48 


THE  LABORATORY. 


Fig.  48 


Wherever  gas  can  beohtiilned,  it  furnishes  at  once  the  best  and  most 
economical,  as  well  as  safest,  fuel  for  blowpipe  work.  Those  who  prefer 
the  detached  flame  and  simple  form  of  blowpipe,  which  may  be  used 
either  by  the  mouth  or  foot-blower,  to  the  more  recent  compound  ap- 
paratus of  Mr.  Fletcher,  may  readily  con- 
struct a  burner  which  will  be  found  to 
answer  every  re(|uirement  of  the  labora- 
tory by  attaching  to  the  base  of  an  ordi- 
nary Bunsen  burner,  which  may  be  ob- 
tained at  the  dental  depots  (see  Fig.  48), 
a  piece  of  brass  tubing  (i  inches  in  length 
by  1|  inches  in  diameter.  Over  the  top 
of  this,  in  order  to  properly  .spread  the 
flame,  a  piece  of  fine  bnuss-wire  gauze  is 
fastened  by  means  of  a  ring  of  sheet 
brass  J  incli  in  width.  Connection  may 
be  made  with  the  gas  bracket  in  almost 
any  part  of  the  room  by  means  of  flexi- 
ble rubl)er  tubing. 

The  "automaton  blowpipe,"  a  some- 
w4iat  recent  improvement  of  Mr.  Fletch- 
er's, intended  for  general  laboratory  use 
and  much  employed  by  experts  in  crown  and  bridge-work  where  gas  is 
available,  is  of  the  t^-pe  of  mechanical  blowpipes  which  has  quite  super- 
seded the  mouth  blowpipe  in  most  soldering  operations.  The  blast  may 
be  supplied  by  either  the  English,  Burgess,  or  Fletcher  foot-blower.  The 
supply  of  gas  and  air  is  controlled  by  a  longitudinal  movement  of  the  tube, 
worked  by  a  spring  under  slight  pressure  of  the  hand  when  it  is  held  as 


Gas  burner  for  use  with  mouth  blowpipe. 


Fig.  49 


Automaton  blowpipe. 


shown  in  the  illustration  (Fig.  49).  This  is  sufficient  to  give  either  a 
pointed  jet  or  a  full-sized  flame  at  will.  The  gas  passage  does  not  close 
entirely,  but  allows  of  the  escape  of  enough  gas  to  prevent  the  flame  from 
going  out  when  the  blowpipe  is  not  in  use,  and  it  may  be  hungup  by  the 
ring  which  is  attached  to  it  when  it  is  desirable  to  get  it  out  of  the  hand. 


SOLDERING  APPARATUS  AND  ACCESSORIES. 


49 


Fig 


Mr.  Fletcher  has  devised  a  foot-blower,  shown  in  Figs.  52  and  53, 
which  may  be  used  with  any  form  of  bh)wpipe.  The  reservoir  of  the 
upper  portion  (Fig.  52)  which  holds  the  air  is,  when  the  bellows  is  not  in 
operation,  merely  a  disk  of  thick  cof- 
fer-dam rubber,  which  expands  under 
the  pressure  of  the  air  while  tlie  bel- 
lows is  in  motion,  and  thus  affords 
a  compact,  powerful,  and  effective 
arrangement.  The  step  for  the  foot 
is  very  low,  and  the  blower  may  be 
used  with  ease  whether  the  operator 
is  standing  or  seated.  The  pressure 
is  steady  and  equal,  and  if  the  rub- 
ber disk  is  distended  until  forced 
against  the  net,  it  can  be  increased 
to  almost  any  extent  desired,  and  will 
give,  if  required,  a  heavy  and  con- 
tinuous blast  through  a  pipe  of  J-inch 
clear  bore. 

Recently,  a  small  rotary  compressor 
has  been  put  on  the  market,  which, 
when  run  by  a  motor,  as  the  lathe 
motor,  for  example,  supplies  a  very 
satisfactory  current  of  air  to  operate 
a  blowpipe.  This  is  shown  in  Fig. 
51.  Many  laboratories  at  the  pres- 
ent time  are  supplied  with  compressed  air,  which,  if  obtainable  in  sat- 
isfactory amount,  is  the  best  source  of  air  for  extensive  soldering  opera- 
tions.    A  pressure  regulator  should  be  connected  at  the  outlet  for  the 

Fig.  51 


English  double-acting  foot-bellows. 


AIR  OUTLET 


Rotary  air  compressor. 


blowpipe  supply,  as  no  stop-cock  can  regulate  the  flow  accurately.  A 
pressure  of  from  two  to  four  pounds  is  correct  for  the  ordinary  blow- 
pipe.    In  small  operations,  where  great  delicacy  is  required,  the  mouth 


50 


THE  LABORATORY. 


supply  method  insures  greater  satisfaetion  because  it  is  always  under 
perfect  control. 

Dr.  George  W.  Melotte  has  devised  a  blowpipe  especially  for  use  in 
crown  and  bridge-work,  which  is  in  many  respects  similar  to  the  pre- 
ceding. The  gas  is  supplied  through  a  valved  tube  (Fig.  54)  by  connect- 
ing it  with  rubber  tubing  to  a  gas  bracket.  The  spring  valve  which  regu- 
lates the  supply  of  gas  maybe  set  by  means  of  a  thumb-screw  and  jam- 
nut  to  a  flame  of  any  desired  size.  For  delicate  soldering  it  may  be  used 
with  air  current  from  the  mouth  by  attaching  a  tul)e  and  mouth-piece  to 
the  longer  pipe  (Fig.  54).  The  method  of  using  it  as  a  hand  blowpipe 
is  illustrated  in  Fig.  55.  It  can  also  be  used  with  the  foot-bellows  when 
a  more  powerful  blast  is  required,  or  with  nitrous  oxide  to  procure  an 
oxyhydrogen  flame. 

The  blowpipe  designed  by  Dr.  F.  H.  Lee  is  shown  in  the  illus- 
tration (Fig.  56).  It  is  provided  wnth  a  mouth-piece  with  rubber 
tubing,  so  that  it  can  be  operated  by  the  mouth,  or,  by  removing  this 


Foot-bellows. 


Foot-bellow.' 


attachment,  with  the  foot-blower.  The  flame  is  controlled  by  the  spring 
lever  so  accurately  that  a  fine  flame  can  be  directed  upon  a  particular 
spot.  Releasing  the  lever  shuts  off  the  gas  supply,  allowing  only  enough 
to  escape  to  keep  the  flame  lighted  for  future  use. 

A  most  ingenious  blowpipe  for  the  soldering  of  regulating  appliances 
and  other  small  operations  in  which  very  delicate  manipulation  is  re- 
cjuired  has  been  devised  by  Dr.  J.  G.  Lane  (Fig,  57).  It  is  designed  for 
use  with  air  current  supplied  by  the  mouth,  and  may  be  fixed  upon  the 
table,  leaving  both  hands  free  to  handle  the  articles  being  soldered. 
The  bell-shaped  mouth  reduces  to  the  minimum  the  possibility  of  extin- 
guishing the  flame  by  too  hard  a  blast.  The  tube  which  carries  the  air 
is  carefully  tapered  to  its  outlet,  where  it  corresponds  in  size  to  No.  25 
standard  wire  gauge,  the  effect  of  which,  when  the  air  is  forced  through 
under  high  pressure,  is  to  produce  a  very  finely  pointed  flame,  in  which 
nearly  perfect  combustion  takes  place,  and  in  consequence  a  high  degree 
of  heat  is  produced.  This  fine  flame  permits  very  accurate  localizing 
of  the  heat.  A  great  advantage  in  the  soldering  of  small  articles  is  found 
in  the  horizontal  direction  of  the  flame  when  the  air  is  forced  through 


SOLDERING  APPARATUS  AM)  ACCESSORIES. 


51 


the  blowpipe.    As  soon  as  the  solder  flows  the  operator  ceases  to  blow,  and 
the  flame  is  immediately  removed  from  the  article  soldered.     If  the  blow- 
pipe were  directed  vertically,  stoppage  of  the  air-current  would  not  have 
this  efl'ect,  and  the  article  itself  would  have 
to  be  moved.  ^^'°-  '"''* 

There  are  other  forms  of  automatic  blow- 
pipes (Fig.  58),  which  are  mounted  on  iron 
bases  and  provided  with  a  ball  joint,  so  as 
to  be  self-retentive  and  adjustable  at  the 
will  of  the  operator 

The  hot-blast  blowpipe  devised  by  INIr.  Fletcher,  shown 
in  Fig.  59,  possesses  a  power  but  little  inferior  to  the  oxy- 
hydrogen  blowpipe.  It  fuses  pure  gold  without  difficulty, 
and  is  therefore  of  great  value  as  a  soldering  appliance  in 
continuous-gum  work,  where  either  pure  gold  or  its  alloy, 
with  platinum,  is  used  as  the  solder. 

In  this  instrument  the  air  pipe,  as  will  be  seen,  is  coiled 
around  the  gas  pipe,  and  both  are  heated  by  three  small 


Fig.  55 


-1^^^ 


Method  of  using  Melotte's  blowpipe. 

Bunsen  burners,  the  gas  supply  to  which  is  controlled  by 
a  separate  stopcock.  The  air  blast  is  obtained  by  a  foot- 
blower  connected  with  the  blowpipe  by  means  of  a  flex- 
ible rubber  tube.     (^See  Fig.  59.) 

Where  gas  is  not  available,  a  simple  and  perfectly  safe 
blowpipe,  made  expressly  for  use  with  gasoline  gas,  has 
been  devised  which  possesses  a  power  and  efficiency  fully 
equal  to  that  obtained  from  coal-gas.  As  shown  in  Fig.  60, 
it  is  provided  with  a  generator  (.4)  which  requires  a  supply 
of  air  under  pressure,  and  is,  therefore,  operated  in  connec- 
tion with  a  foot-bellows  (B).  To  charge  the  generator,  pour  gasoline  in  the 
funnel  which  comes  with  the  apparatus  and  which  has  been  screwed  down 
tight  in  the  filler  tube.  Wlien  the  gasoline  rises  in  the  funnel  it  is  an  indi- 
cation that  the  requisite  quantitv  has  been  poured  in,  the  reservoir  then 


Melotte's  blowpipe. 


52 


THE  LABORATORY. 


beinor  about  one-half  full.     The  interior  of  the  generator  contains  a  large 
evaporating   surface,  and  is  provided  with  safety  gauzes  to  prevent  a 


Fig.  56 


Fio.  57 


1 


Lane's  hhnvpiiie  for  regulating  appli- 
ances. 

Fig.  58 


Lee's  blowpipe. 


Blowpipe  adjustable  on  movable 
stand. 


flashing  back  of  the  flame.  The  turret  top  controls  with  a  triple  valve 
the  various  outlets  and  inlets,  so  that  they  may  be  all  opened  or  closed 
with  one  motion.     With  the  blowjjipe  and  blower  connected  to  the  gen- 


SOLDERING  APPARATUS  AND  ACCESSORIES.  53 

erator  (as  shown  in  the  illustration),  it  is  only  necessary  to  operate  the 
blower  to  obtain  the  gas  ready  for  use.  The  air  thus  forced  through 
the  apparatus  is  highly  charged  with  gasoline  vapor,  and  the  mixture 
burns  with  a  considerable  degree  of  heat.  The  turret  should  be  turned 
to  the  left  to  open  the  valves.  The  size  and  character  of  the  flame  are 
controlled  by  the  valve  of  the  blowpipe  shown  in  Fig.  61. 

Different  samples  of  gasoline  will  often  be  found  to  vary  in  quality. 
When  a  few  drops  of  a  good  quality  of  this  material  are  poured  on  a 
plate,  it  should  evaporate  quickly  and  completely,  leaving  no  greasy 
residue :  74°  to  76°  gasoline,  such  as  is  commonly  used  in  "  vapor  stoves" 
for  culinary  purposes,  is  suitable  for  use  in  the  "gasoline  generator  and 
blowpipe."  The  heavier  hydrocarbons  or  naphthas  will  not  give  as  good 
results.  It  is  important  that  all  the  tubing  used  in  connection  with  this 
apparatus  be  kept  in  good  order,  otherwise  its  power  may  be  greatly 
reduced.     If  the  gasoline  is  of  inferior  quality  and  contains  the  heavier 

Fig.  59 


Hot-blast  blowpipe. 

oils,   the  generator  will  not  work  satisfactorily;  it  will  then  require 
emptying  and  refilling  with  a  better  quality  of  gasoHne. 

Heat-producing  devices  built  upon  a  new  principle  and  using  gasoline 
as  a  fuel  have  recently  been  introduced  into  use.  They  are  reliable, 
produce  a  high  degree  of  heat,  and  in  careful  hands  are  perfectly  safe. 
In  localities  where  no  gas  supply  exists,  every  laboratory  need  may  be 
met  by  them.  A  blowpipe  of  this  type  which  has  great  heat-producing 
capacity  is  illustrated  in  Fig.  62.  It  consists  of  a  reservoir  of  brass,  built 
strongly  enough  to  stand  considerable  pressure.  This  is  filled  with 
gasoline  to  the  point  permitted  by  the  funnel  shown  in  the  illustration, 
and  the  filler  plug  is  screwed  down  tight.  Then  air  is  forced  in  by  means 
of  the  pump  in  the  handle  of  the  apparatus,  the  gauge  indicating  the 
amount  of  pressure  thus  obtained,  until  about  forty  pounds  to  the 
square  inch  is  registered,  when  the  valve  at  the  bottom  of  the  pump 
should  be  closed  to  prevent  the  escape  of  the  gas. 


54 


TJIK  LABORATORY. 


The  burner  (Fig.  G3),  to  which  the  high  heat  efficiency  of  tlie  appliance 
is  due,  consists  of  a  combustion  chamber  (O)  to  which  the  gas  is  admitted 
in  two  jets  (Z)  and  J)),  two  needle  valves  controlling  the  jets,  and  a  cup 
(G)  underneath,  which  serves   for  the  initial  heating  of   the   burner. 


Fig.  60 


Gasoline  blowpipe  apparatus.    A.    Geuerator.    B.    Foot-blower. 
Fig.  61 


Gasoline  blowpir)e. 


This  cup  is  filled  with  gasoline  which  is  lighted,  and  when  nearly  burned 
out  the  lower  valve  {E)  is  opened  and  the  burner  lighted.  The  upper 
valve  (F)  is  then  opened,  which  carries  a  mixture  of  air  and  gas  through 
the  centre  of  the  chamber,  blows  the  flame  in  the  proper  direction,  and 


SOLDERING  APPARATUS  AND  ACCESSORIES. 


55 


also  furnishes  oxygen  for  the  combustion  of  the  gas  obtained  from  the 
lower  jet.     The  burner  continues  to  heat  the  gasoline  forced  up  by  the 


Fig.  62 


GasoUne  blow  pipe  and  beater. 


air  pressure,  and  it  is  converted  into  gas  by  contact  with  the  hot  metal, 
so  that  its  operation  is  continuous  and  limited  only  by  the  supply  of  fuel 
and  by  the  air  pressure  which  must  be  kept  up.  To  secure  the  best  results , 
a  correct  adjustment  of  the  two  valves  is  necessary,  and  definite  instruc- 
tions   for   this   accompany    the    apparatus.     It    is  claimed    that  heat 


Fig.  63 


Burner  for  gasoline  blowpipe. 


of  3000°   F.  to    3500°   F.  may  be  obtained  with  the  appliance.    The 
swivels  permit  the  burner  to  be  turned  in  any  direction.    It  may  be  used 


56 


THE  LAIiORATORY. 


Fig.  04 


Gasoline  Bimsen  burner. 


as  a  Mowpipe  to  flow  2")  jht  cent.  ]>latiiiuiii  solder,  to  heat  the  furnaee 
in  continuous-gum  and  porcelain  crown  work,  or  a    furnace  used  in 

inching  the  more  refrac-tory  metals, 
A  heater  constructed  upon  the  prin- 
ci])le  of  tlie  Bunscn  gas  1  turner,  which 
will  be  found  most  useful  for  the  smal- 
ler heating  operations  is  shown  in  Fig. 
C4.  Recently  a  blowpipe  burning 
wood  alcohol  made  upon  the  same 
principle  as  the  blowpipe  described 
above  has  been  introduced 

Supports.  In  melting  small  quan- 
tities of  gold  or  silver  or  in  soldering 
with  the  blowpipe  flame  it  is  necessary 
to  perform  these  operations  u])on  a 
support  made  of  some  suitable  body, 
such  as  charcoal,  coke,  pumice-stone, 
or  asbestos  and  plaster,  charcoal  and 
plaster,  etc. 

Well-burned  charcoal  is  especially 
suited  for  both  purposes,  as  it  helps  to 
increase  the  heat,  and  in  the  putting 
together  of  small  quantities  of  gold  or 
silver  solders  prevents  oxidation  of  the 
base  metals  which  are  added  to  reduce  the  fusing  point  of  the  alloy  and 
cause  it  to  flow  freely.  Charcoal  made  from  the  light  woods,  such  as 
pine,  is  best,  because  it  is  not  so  likely  to  throw  sparks  when  the  flame 
is  directed  upon  it  as  are  the  harder  coals,  such  as  that  made  from 
oak;  and,  being  softer,  it  is  much  better  adapted  to  soldering  operations 
in  which  it  is  necessary  to  hold  the  pieces  to  be  united  together  by 
means  of  small  nails  or  tacks  thrust  into  the  support;  as,  for  instance, 
where  a  rim  is  to  be  soldered  to  a  plate,  the  former  must  be  brought 
in  contact  with  the  latter  upon  the  charcoal,  and  so  held  during  the 
preliminary  soldering,  which  consists  of  uniting  the  rim  to  the  plate  with 
a  small  piece  of  solder  at  some  one  point,  after  which  the  accurate  adjust- 
ment of  the  rim  to  the  plate  for  final  soldering  is  rendered  much  easier. 
A  good  solid  piece  of  charcoal,  sufficiently  large,  should  be  selected, 
and  bound  with  iron  or  copper  wire  to  prevent  its  breaking  into  pieces. 
It  should  then  receive  a  coating  of  plaster,  from  a  quarter  to  a  half  inch 
in  thickness,  on  all  sides  except  the  one  upon  which  the  object  to  be 
soldered  is  to  rest.  This  adds  to  its  strength  and  prevents  soiling  the 
fingers  while  it  is  being  handled,  (jood  charcoal,  suitable  for  use  in  the 
dental  laboratory,  cannot,  however,  always  be  found  when  wanted,  and 
it  is  therefore  often  necessary  to  use  some  other  substance  which  may  be 
more  easily  obtained.  Thus  those  living  in  large  cities  may  be  com- 
pelled to  employ  pieces  of  coke  as  supports  in  soldering.  Next  to  char- 
coal, coke  is  most  suitable  for  this  purpose.  It  is  more  durable  than 
charcoal,  and  when  such  a  support,  composed  of  one  large  piece  or  even 


SOLDERING  APPARATUS  AND  ACCESSORIES  67 

several  smaller  pieces,  is  bound  together  with  wire  and  coated  with 
plaster,  it  will  last  a  long  time.  Large  pieces  of  pumice-stone  also 
answer  well  for  the  purpose  of  holding  small  objects  while  the  flame  of 
the  blowpipe  is  directed  upon  them.  Neither  of  these,  however,  is  so 
well  adaptetl  as  charcoal  for  holders,  when  small  fjuantities  of  metals 
are  to  be  melted,  in  consequence  of  their  greater  porosity  and  their  hard- 
ness, which  prevent  the  cutting  of  suitable  pits  for  the  reception  of  the 
metal  to  be  fused. 

A  very  good  support  for  soldering  purposes  alone  may  be  formed  by 
filling  a  cup  made  of  sheet  iron  or  copper,  5  inches  in  diameter  by  5 
inches  in  depth,  with  a  mixture  of  asbestos  and  plaster  or  plaster  and 
finely  broken  charcoal.  The  vessel  should  be  supplied  with  a  wooden 
handle,  fastened  in  the  bottom,  for  convenience  in  handling. 

Plattner's  Manual  of  Qualitative  and  Quantitative  Analysis  with  the 
Blowpipe  gives  a  method  of  artificially  preparing  good  solid  supports 
of  charcoal  which  might  be  found  of  value  in  the  dental  laboratory. 
It  consists  of  mixing  charcoal  dust  (which  must  not  be  too  finely  ground) 
with  starch  paste.  The  latter  is  prepared  by  combining  1  part  of 
starch  with  6  parts  of  boiling  water.  These  are  stirred  in  an  earthen 
pot  until  all  the  meal  is  converted  into  paste.  This  paste  is  rubbed  in  a 
porcelain  mortar  with  frequent  additions  of  rharcoal  dust  until  the  mass 
becomes  too  tough  for  further  admixture,  w^hen  enough  of  the  coal-dust 
is  kneaded  in  with  the  hands  to  render  the  whole  mass  stiff  and  plastic. 
From  this  the  desired  fornos  of  supports  can  be  made,  allowed  to  dry 
gradually  and  thoroughly,  and  then  heated  to  redness  in  a  covered 
vessel,  so  as  to  char  the  starch  paste.  The  charring  may  be  regarded  as 
complete  when  the  evolution  of  gases  from  the  mass  ceases  or  when  it 
has  been  heated  to  dull  redness.  Coals  thus  formed  are  of  the  proper 
firmness,  and  ring  like  ordinary  good  charcoal  when  thrown  on  the 
table. 

Blocks  formed  of  graphite  and  fire-clay  are  now  often  used  as  supports 
for  holding  objects  to  be  soldered.  These  are  by  no  means  perfect 
non-conductors,  and  when  used  without  some  protection  to  the  hand 
they  soon  become  so  hot  in  the  operation  of  soldering  that  it  is  impossible 

Fig  65  Fig.  66 


Soldering  support.  Soldering  support  and  handle. 

to  hold  them  for  any  length  of  time.  To  overcome  this  difficulty,  how- 
ever, a  very  convenient  device  for  holding  the  carbon,  graphite,  or 
other  support  has  been  introduced.     (See  Figs.  65  to  67.) 

Soldering  blocks  have  recently  been  formed  of  asbestos,  and  have 
found  favor  with  many  in  preference  to  the  "carbon  block"  for  solder- 


58 


77//-;  LABORATORY. 


ini'-  purposes,     'i'ht'y  are  eircular,  (le})res.se(l  on  each  face,  and  4  inches 
in  diameter. 

The  carbon  cylinder,  made  of  the  same  composition  as  the  carbon 
block,  is  a  new  form  of  support  admirably  adapted  for  soldering  small 


Fig.  67 


Fig.  68 


Asbestos  soldering  surijifrt  with  handle  detached. 


Solderiiit,'  support  for 
small  articles. 


articles,  such  as  gold  crowns,  or  for  blowpipe  assays.     In  size  it  is  1| 
inches  in  diameter  by  3  inches  in  length  (Fig.  68). 

Among  the  more  recently  introduced  forms  of  asbestos  soldering 
and  melting  supports  are  those  shown  in  the  annexed  illustrations. 
Fig.  69  represents  a  combined  soldering,  melting,  and  ingot  block,  6 


Fig.  69 


Combined  soldering,  melting,  and  casting  block. 
Fig.  70 


Soldering  block. 


inches  long,  2|  inches  wide,  by  h  inch  in  thickness.  Fig.  70  shows 
an  asbestos  support  intended  exclusively  for  soldering,  4h  inches  in 
diameter  by  If  inches  high,  with  concave  top,  and  provided  with  a  con- 
venient holder,  which  also  prevents  the  support  from  being  laid  flat 
upon  the  table  while  hot. 


SOLDERING  APPARATUS  AND  ACCESSORIES 


59 


Fn;.  71 


Laboratory  burner. 


The  best  method  of  "  heating  up  "  a  denture  })reparatory  to  soldering 
is  to  phice  it  over  a  burner  sueh  as  is  eni])l()ye<l  in  tlie  dental  laboratory 
for  melting  lead  and  zine  and  for  general 
heating  purposes  (Fig.  71 ).  A  ring  of  cast 
or  sheet  iron,  0  inches  in  diameter  by  2 
inches  high,  should  then  be  placed  around 
it  for  the  purpose  of  holding  the  charcoal, 
which,  in  pieces  the  size  of  a  hen's  egg, 
should  be  built  around  the  outside  of  the 
denture  so  that  it  maybe  uniformly  heated. 

A  more  recent  device  which  has 
proved  most  satisfactory  is  a  grill  of 
heavy  iron  wire,  which  permits  the  heat 
to  reach  the  invested  piece  and  yet  ab- 
sorbs a  lot  of  heat  itself,  and  thus  main- 
tains the  denture  at  a  more  constant 
temperature.  This  is  especially  true 
if  charcoal  or  pieces  of  pumice  stone  are 
heaped  about  the  invested  article. 

The  cone  or  top  of  tlie  apparatus  just 
described  may  now  be  placed  over  it.  The 
gas  is  then  lighted,  but  the  full  head 
should  not  be  turned  on  until  the  moisture 
of  the  investment  has  been  driven  off,  when 
it  may  be  gradually  increased  until  the 
piece  is  heated  to  redness.  About  thirty  minutes  will  be  required  for 
heating  up,  when  the  top  may  be  removed  and  the  piece  raised  to 
a  red  heat  by  means  of  the  full  flame  of  the  blowpipe.  The  live  coals 
used  in  heating  up  should  also  be  placed  around  the  outside  of  the 
investment  to  prevent  the  too  rapid  cooling  of  the  piece  should  any  delay 
in  the  soldering  occur.  When  the  latter  operation  has  been  satisfactorily 
completed,  the  top  may  be  placed  tightly  on  and  all  access  of  air  pre- 
vented, in  order  that  the  piece  may  cool 
slowly  and  thus  avoid  the  danger  of  crack- 
ing the  teeth. 

The  "Lewis"  combined  case  heater  and 
soldering  cup  (Fig.  72)  is  a  recently  im- 
proved device  for  drying  out  and  solder- 
ing an  invested  piece  of  gold  work  without 
removing  until  completed.  It  consists  of 
an  iron  cup  or  hemisphere,  with  suitable 
openings  for  the  admission  of  heat  from 
below,  supported  by  another  iron  cup 
attached  to  an  improved  Bunsen  burner 
and  rotating  on  it.  The  upper  hemisphere 
is  capable  of  being  swivelled  or  tilted  in 
any  position  desired  to  facilitate  the  flowing 

of  the  solder  and  to  bring  all   parts    under  combined  case  beater  and 

,1  ,.  p    ,1        1  1  •  soldering  cup. 

trie  action  oi  the  blowpipe. 

The  cup  is  filled  with  pieces  of  broken  pumice  or  coils  of  asbestos 


Fig.  72 


60 


THE  LABORATORY. 


rope,  upon  which  the  case  rests.     To  dry  out  an  invested  denture  it  is 
arranged  in   the  cup,  the  burner  liglited",  and  tiie  cover  placed  on  to 


Fio.  73 


Cajife-lieater  ami  Mjlilering  fup  in  use. 


retain  the  heat.  After  thoroughly  drying,  which  should  be  preliminary 
to  the  final  heating,  the  temperature  should  be  raised  by  increasing  the 
flow  of  gas  until  the  whole  piece  has  assumed  a  dull-red  appearance, 
when  the  top  cover  may  be  removed,  the  cup  tilted  to  a  convenient 


Fig.  74 


Fig.  75 


)lder  tWL-ezers. 


position,  the  blowpipe  brought  into  use,  and  the  soldering  finished. 
The  burner  underneath  should  remain  lighted  during  the  entire  oper- 
ation. The  position  or  angle  of  the  cup  may  be  changed  by  a  slight 
pressure  with  the  blowpipe  on  its  flanged  edge. 


PICKLING  SOLUTIONS.  61 

Suitable  solder  tweezers,  designed  for  placing  pieces  of  solder  uj)on 
parts  to  be  united  are  important  accessories  of  the  soldering  table. 
Figs.  74  to  76  show  the  ordinary  forms  of  these,  while  Fig.  7<S  shows 
a  pair  with  long  reach,  suitable  for  placing  solder  on  a  case  while  it  is 
hot.  The  solder  tongs,  shown  in  Fig.  79,  will  be  found  most  convenient 
in  handling  invested  pieces  during  the  soldering  process,  and  a.s  muffle 
tongs  in  baking  porcelain  crowns  and  bridges. 

Wire  clamps  are  indispensable  in  a  certain  class  of  soldering  oper- 
ations, and  a  small  collection  of  different  sizes  of  such  forms  as  are 

Fig.  77 


Wire  clamps. 

show^n  in  Fig.  77,  made  of  No.  14  iron  wire,  should  always  be  kept  on 
hand  ready  for  use.  The  smaller  clamps  shown  in  the  illustration  are 
especially  useful  in  the  construction  of  lower  metallic  plates.  When  two 
thin  pieces  have  been  swaged  separately,  with  a  view  to  uniting  them  by 
soldering,  there  is  always  danger  of  their  being  forced  apart  by  the 
calcination  of  the  borax  which  is  present  as  a  flux,  and  by  expansion 
when  the  heat  is  applied ;  it  is  necessary,  therefore,  to  hold  them  together 
temporarily  until  the  preliminary  or  partial  soldering  is  accomplished. 

In  soldering  a  chamber  cap  to  an  upper  plate  the  cap  is  almost  certain 
to  change  its  relation  to  the  plate  during  the  soldering  unless  secured 
in  situ  by  a  stout  wire  clamp.  For  this  purpose  it  is  well  to  have  on 
hand  a  few  different  sizes  of  the  larger  clamp  showai  in  Fig.  77. 

Pickling  Solutions. — After  removing  the  investing  materials  from 
around  the  soldered  dentures — ^which,  however,  should  never  be  done  if 
porcelain  teeth  are  present  until  the  case  has  been  allowed  to  cool  slowly 
and  perfectly — it  may  be  placed  in  a  pickling  solution  composed  of 
sulphuric  acid  1  part,  water  4  parts,  for  the  purpose  of  dissolving  the 
fused  borax  and  the  oxide  of  copper  which  darkens  the  surface  of  gold  or 
silver  into  which  it  usually  enters  as  an  alloy.  Dilute  sulphuric  acid  will 
dissolve  both  at  ordinary  temperatures,  but  its  action  may  be  greatly 
hastened  by  heating  it  to  212°  F.  The  oxide  is  converted  into  a  solulile 
sulphate  which  is  dissolved  by  the  water  present  in  a  dilute  solution,  the 
undiluted  acid  being  less  efficient  as  a  pickle.  This  may  be  done  in  a 
copper  pickling  pan,  such  as  is  sold  for  the  purpose  at  the  dental  depots, 
(see  Fig.  SO),  or  in  a  Wedgwood  evaporating  dish,  similar  to  those  used 
by  chemists.  A  porcelain  casserole  {Y\g.  81)  is  a  very  useful  container 
for  the  pickle.  It  should  be  mounted  on  a  chemist's  tripod.  Sulphuric 
acid  is  corrosive  and  destructive  to  the  clothing;  hence,  ordinary  glass 
vessels  are  not  safe  in  which  to  heat  the  solution   on  account  of  their 


62 


THE  LABORATORY. 

Fig.  78  Fig.  70 


Long  solder 
tweezers. 


\ 


Solder  tongs. 


PORCELAIN  FURNACES. 


63 


liability  to  fracture,  and  })()rcelaiii  ware  of  the  cjuality  usually  made  for 
domestic  use  will  not  retain  the  acid,  which  soon  dissolves  the  glazing 
from  the  surface,  after  which  it  is  liable  to  escape  through  the  bottom 
of  the  vessel. 

A  strong  solution  of  common  alum  may  be  used  instead  of  the  acid, 
but  it  must  be  heated  to  the  boiling  point  to  develop  its  solvent  properties. 

Fig.  80 


I'ickling  pan. 


^Mlen  the  same  pickling  solution  has  been  used  a  number  of  times  it 
becomes  quite  green  in  color,  and  crystals  of  sulphate  of  copper  (CuSO,) 
form  around  the  edge  of  the  pan.  These  are  the  result  of  the  action  of 
the  acid  upon  the  oxide,  and  they  redissolve  when  the  solution  is  again 


Fig.  81 


Porcelain  casserole  for  use  in  pickling. 

heated.  The  sulphate  is  decomposed  by  electrolysis,  and  more  or  less 
metallic  copper  is  probably  always  deposited  upon  the  plate,  and  remains 
under  the  teeth  in  inaccessible  places  after  the  denture  is  finished;  hence 
the  "coppery"  taste  sometimes  complained  of  in  newly-soldered  dentures 
when  first  inserted.  This  may  be  remedied  in  the  case  of  a  gold  denture 
by  immersion  in  a  weak  solution  of  nitric  acid  and  water;  and  if  the 
denture  is  of  silver — which  metal  would  be  acted  upon  by  nitric  acid — 
boiling  in  a  strong  solution  of  alum  is  recommended. 

Where  a  fume  closet  with  flue  communicating  with  the  outside  air 
can  be  placed  in  the  laboratory,  it  will  be  of  great  advantage  in  confining 
the  vapors  from  pickling  solutions  and  preventing  their  deleterious 
action  upon  the  exposed  steel  instruments. 

Porcelain  Furnaces.— Furnaces  for  the  fusing  of  porcelain  for  inlays, 
crown  and  bridge-work,  and  continuous-gum  have  of  late  years  been 
improved  to  such  an  extent,  and  are  in  such  general  use,  that  it  has  been 
deemed  wise  to  discuss  them  briefly  in  this  chapter.  They  were  origi- 
nally placed  in  the  dental  laboratory  for  the  baking  of  block  teeth,  single 
teeth,  or  for  use  with  the  continuous-gum  process.  They  were  exceed- 
ingly bulky,  occupying  so  much  space  that  they  could  not  be  placed  in 
the  smaller  laboratories,  required  a  high  chimney  for  draught,  and  were 


64 


THE   LABORATORY. 


dirty  and  unsatisfactory  in  their  working  in  most  ways.  Anthracite  coal 
was  used  as  the  fuel,  and  as  the  furnace  had  to  be  charged  for  each 
burning  the  process  re(juired  considerable  time.  The  first  important 
modification  of  the  old-fashioned  furnace  was  made  by  Dr.  Ambler 
Tees,  in  1880.  He  reduced  the  size  of  the  apparatus,  and  decreased  the 
time  necessary  to  operate  it.  Coke  was  used  as  the  fuel.  Following 
upon  this  was  the  attempt  to  use  gaseous  or  li(|uid  instead  of  solid  fuels, 
and  furnaces  after  the  patterns  of  C.  H.  Land,  A.  B.  ^^errier,  and  John 
H.  Meyer  were  a  great  advance  over  the  others.  They  economized 
time,  were  more  easily  heated  up,  and  in  general  operated  more  satis- 
factorily than  the  solid  fuel  furnaces.  These  still  failed  to  infallibly 
provide  against  the  "  gasing  "  of  the  porcelain,  and  a  furnace  designed 
by  Downie  by  the  use  of  a  platinum  muffle  removed  this  danger  com- 


Mr 


Ash's  gas  furnace  for  continuous  gum  work. 


pletely.  It  was  designed  for  baking  crowns,  inlays,  gum  sections, 
etc.  A  larger  furnace  operating  by  a  similar  principle  and  suitable  for 
the  baking  of  full  dentures  in  high-fusing  porcelain  is  shown  in  Fig.  82. 
It  has  a  nickel  muffle,  and  the  danger  of  "  gasing,"  which  is  a  factor 
to  be  seriously  considered  in  all  coke  and  gas  furnaces,  is  eliminated  in 
this  furnace  because  the  muffle  is  carried  through  the  fire-clay  lining  to 
the  opening  in  the  iron  casing  on  either  side.  This  arrangement  is 
advantageous  also  in  giving  two  means  of  entrance  into  the  muffle,  so 
that  the  piece  being  fired  can  be  watched  from  both  sides.  The  two 
openings  to  the  muffle  are  closed  by  a  double  set  of  sliding  doors,  which 
are  made  of  iron  with  a  fire-clay  lining  of  ^  inch  thickness,  ^^^len  it  is 
necessary  for  the  operator  to  look  into  the  muffle  the  doors  are  slightly 
moved  apart,  so  that  only  a  minimum  amount  of  heat  escapes.  The 
cooling  can  also  be  regulated  better  by  opening  first  one  side  and  then 
the  other. 


PORCELAIN  FURNACES. 


65 


Fig  83 


The  Christensen  drauglit  gas  furnace  (Fig.  83)  was  one  of  the  first 
to  be  used  without  an  air  blast.     This,  of  course,  meant  a  great  saving 
in  labor,  especially  where  a  foot-blower  was  in  use.     The  roar  which  is 
such  a  drawback  in  gas  furnaces  is  considerably 
lessened,  but  by  no   means  done  away  with  in 
this  furnace.    To  get  the  highest  temperature  the 
gas  must  be  so  regulated  as  to  obtain  the  greatest 
possible  roar  in  the  burner. 

This  furnace  also  has  a  nickel  mufHe  3  inches 
long,  1^  inches  high  and  1^^  inches  wide,  which 
makes  it  useful  for  inlays,  crowns,  and  small 
bridges.  The  draught  is  obtained  by  a  chimney 
18  inches  high,  being  placed  in  the  centre  of  the 
casing  directly  above  the  muffle.  The  three 
Bunsen -burners  which  supply  the  heat  are  ar- 
ranged in  a  row  so  that  the  flames  envelope  the 
muffle  equally  along  the  whole  of  its  length, 
producing  an  even  temperature  inside  the  muffle. 

Recently  furnaces  for  fusing  porcelain  utilizing 
gasoline  have  been  introduced.  The  tempera- 
ture obtainal^le  in  them  is  sufficient  to  bake  anj 
of  the  most  refractory  porcelains,  except  block 
tooth-body,  a  temperatin-e  of  3000°  being  claimed 
as  possible.     The  heater  of  the  furnaces  of  the 

Turner  Brass  Works  is  of  the  blowpipe  type,  described  on  page  53, 
the  furnace  itself  consisting  of  a  cast-iron  sheU  lined  with  fire-clay, 
with  a  seamless  nickel  muffle  spun  out  of  one  piece  of  metal.     (Figs. 


Christensen's  Gas  Furnace. 


Fig.  84. 


Gasoline  furnace  for  inlays  and  crowns. 


84  and  85.)  The  furnace  designed  by  Dr.  R.  C.  Brophy  (Fig.  86) 
is  somewhat  similar  in  construction,  having,  however,  a  cast-iron  seam- 
less reservoir  for  the  gasoline  and  being  attached  permanently  to  the 


G6 


THE  LABORATORY. 


furnace.  In  these  appliances  the  necessity  for  continuous  blast  with 
the  foot-blower  is  clone  away  with,  and  with  pr()])er  care  they  are  per- 
fectly safe.  I'hc  principal  objection  to  be  urged  against  them  is  that 
which  obtains  with  the  blast  gas  furnaces,  and  that  is  the  noise  of  oper- 


Fio.  85 


Gasoliue  furnace  for  crowns  and  bridges. 


ation,  but  when  It  is  remembered  that  they  may  be  used  in  any  locality, 
as  they  are  independent  of  gas  or  electric  supply,  and  possess  a  high  degree 
of  efficiency,  their  value,  especially  to  the  country  practitioner,  at  once 
becomes  apparent,  and  the  objection  on  the  score  of  noise  becomes 
relatively  of  no  moment. 


Fig. 


Brophy's  gasoline  furnace. 


Electric  heat  for  the  fusing  of  porcelain  is  now  receiving  extensive 
application,  and  the  means  of  utilizing  so  valuable  an  agent  for  this 
purpose  are  constantly  being  improved.  To  Dr.  L.  E.  Custer*  belongs 
the  honor  of  having  first  made  a  public  demonstration  of  the  method. 


1  October,  1894. 


PORCELAIN  FURNACES.  67 

Heat  is  obtained  from  electricity  according  to  the  following  principle: 
When  an  electric  current  meets  with  a  marked  degree  of  resistance  in 
its  circuit,  heat  is  produced  in  the  effort  to  overcome  that  resistance. 
Platinum  which  has  relatively  low  electrical  conductivity  and  has  a  high 
fusing  point  is  introduced  into  circuit  in  the  form  of  fine  wire,  the  finer  the 
wire  and  the  greater  its  length  the  greater  the  resistance  which  it  offers. 
As  the  platinum  becomes  heated  its  resistance  is  further  increased,  and 
the  heat  produced  likewise  increased,  so  that  by  a  proper  correlation  of 
the  size  of  the  wire  and  its  length  with  the  voltage  of  the  current,  it  is 
possible  to  attain  a  heat  only  limited  by  the  fusing  point  of  the  platinum. 

Electric  heat  possesses  peculiar  advantages  for  the  fusing  of  porcelain. 
As  it  is  not  derived  from  combustion  the  products  of  the  latter  are 
absent,  and  the  danger  of  "gasing"  is  removed.  The  appliance  is  also 
more  cleanly  and  occupies  less  space  and  is  more  convenient  to  use  for 
the  same  reason.  The  accuracy  with  which  the  heat  may  be  controlled 
and  regulated  by  a  rheostat,  and  the  cleanliness,  simplicity,  freedom 
from  noise  and  odors,  and  efficiency  of  this  method  particularly  recom- 
mend it  in  the  laboratory. 

The  110-volt  direct  current  is  the  best  for  operating  an  electric  furnace, 
this  being  usually  the  "power"  current  in  cities.  The  220-volt  direct 
current  may  be  reduced  or  used  directly,  the  furnace  having  been 
specially  wound  for  it,  while  550  volts  is  too  high  to  be  admitted  to  a 
building.  The  52-volt  or  104-volt  alternating  current  may  be  used,  these 
necessitating  also  a  specially  wound  furnace.  The  rheostat,  which 
controls  the  heat  produced  by  a  given  furnace  on  a  circuit  suitable  to  it, 
is  simply  a  fixed  resistance  consisting  usually  of  coils  of  German  silver 
wire,  varying  amounts  of  which  may  be  switched  "in  series"  with  the 
furnace.  The  greater  the  resistance,  the  less  the  current,  and,  therefore, 
the  less  the  heat  generated  by  the  furnace. 

The  liabihty  of  the  platinum  wire  "to  burn  out"  has  been  the  greatest 
drawback  to  full  satisfaction  in  the  use  of  this  class  of  ovens.  The  differ- 
ence between  the  melting  point  of  high-fusing  porcelains  and  the  plati- 
num wire  from  which  the  heat  is  radiated  is  very  small,  yet  it  is  within 
that  narrow  margin  that  the  electric  oven  operates.  Improvements,  how- 
ever, have  recently  been  made  by  Dr.  Custer,^  by  which  the  danger  of 
"burning  out"  has  been  almost  entirely  obviated,  so  that  electric  ovens 
have  been  subjected  to  from  800  to  1200  heatings  without  danger  to  the 
platinum  wire.  This  result  was  effected  by  conforming  the  oven  cavity 
more  closely  to  the  shape  of  the  denture,  and  in  making  every  inch  of  the 
interior  w^alls  heat-producing  surfaces  by  bringing  the  wires  to  the  surface 
so  that  but  little  fire-clay  intervenes  between  the  wire  and  the  object 
heated.  It  was  also  found  that  an  oven  not  spherical  in  shape  would 
become  hotter  in  the  centre,  even  if  the  wires  were  placed  the  same 
distance  apart  all  over  the  surface.  This  difficulty  was  avoided  by 
beginning  at  the  centre  and  arranging  the  wires  closer  together  as  the 
distance  from  the  centre  increased;  by  this  means  perfect  uniformity  of 
heat  was  secured.    Dr.  Custer  observed  that  it  was  always  the  negative 

1  Abstract  of  paper  read  before  the  National  Dental  Association,  Omaha,  September,  1898. 
Ohio  Dental  Journal. 


68 


THE  LABORATORY. 


end  of  the  platinum  wire  tliat  Inirnt  out,  and  that  the  negative  end  of  a 
wire  heated  by  a  constant  electric  current  becomes  about  one-fifth  hotter 
than  the  positive  end.  He  therefore  determined  to  use  thicker  wire 
at  the  nef^ative  end,  by  which  means  he  solved  the  most  perplexing 
problem  in  the  construction  of  electric  ovens. 

In  his  furnace  (I'ig-  S7)  the  wire  is  placed  in  short  curves  to  avoid  great 
displacement  from  the  expansion  in  the  heating,  and  as  it  is  near  the 
surface  great  care  should  be  exercised  to  prevent  the  fusing  of  portions 


Fig.  87 


'SSS^ 


The  Custer  elentrio  oven  No.  2. 


of  porcelain  upon  it,  and  to  prevent  contact  with  a  metallic  instrument 
while  heated  as  a  "burn  out"  might  result. 

The  procedure  in  the  practical  use  of  the  oven  is  exceedingly  simple. 
The  case  is  placed  on  the  tray  in  the  lower  section,  and  the  upper  is  then 
closed  down.  The  lever  of  the  rheostat  used  with  the  furnace  is  placed 
on  the  first  button,  and  heat  for  drying  out  the  case  is  quickly  obtained. 
When  the  operator  is  satisfied  that  there  is  no  more  moisture  j)resent 
he  raises  the  heat  by  pushing  the  lever  to  the  right.  (See  Chapter 
XVI.).  If  he  allows  two  minutes  to  each  button,  it  will  re(|uire  from 
twenty  to  twenty-five  minutes  to  reach  the  fusing  point.  If  it  is  a  crown 
or  bridge  less  time  may  be  consumed  in  raising  the  heat  without  danger 


rORCKLA  IN  FURNA  CKS. 


69 


to  the  case,  and  it  may  l)e  fused  in  from  ten  to  fifteen  minutes  by  tlirow- 
intr  the  lever  over  more  rapidly.  When  the  desired  temperature  has  been 
obtained  and  the  fusing  of  the  poreekiin  is  completed,  the  lever  of  the 
rheostat  is  thrown  back  and  the  current  cut  off.  At  that  instant  the 
heat  begins  to  go  down,  so  that  neither  overfusing  nor  loss  of  brilliancy 
in  the  gum  color  can  occur. 

The  "drop  bottom"  furnace  designed  by  Mr.  W.  A.  Hammond 
(Fig.  88)  has  found  much  favor  with  continuous-gum  workers,  because 
of  the  ability  to  lower  the  bottom  of  the  furnace  containing  the  denture 
for  inspection  during  the  heating  process  without  materially  lowering  the 
heat  of  the  oven.  The  Pelton  furnace  is  of  another  type.  In  this  an 
effort  is  made  to  utilize  the  heat  generated  in  the  rheostat,  and  ordinarily 


Fig    6S 


Hammond  drop  bottom  furnace. 

wasted,  by  winding  the  wires  of  that  instrument  about  the  furnace.  Its 
form  is  shown  in  Fig.  89.  Any  of  these  furnaces  may  be  used  for  crown 
work  or  for  inlay  work,  as  well  as  continuous-gum,  but  as  they  were 
specially  designed  for  the  latter  work,  they  are  rather  too  large  for  such 
delicate  operations.  Smaller  sizes  of  them  may  be  obtained  for  inlay 
and  crown  work.  In  addition  to  these,  the  Mitchell  furnace  No.  1 
(Fig.  90)  is  a  very  simple  one  for  making  inlays  and  crowns.  It  requires 
no  rheostat,  the  current  required  for  it  being  obtainable  from  any  exist- 
ing lamp-socket.  The  wire  is  wound  upon  the  outer  side  of  the  muffle, 
and  so  it  is  easy  to  repair,  because  the  two  ends  of  the  broken  wire  may 
be  easily  seen  when  the  muffle  is  removed. 

^Every  dentist  who  desires  to  make  use  of  an  electric  furnace  ought  to 

'  Manuscript  describing  construction  of  furnace  furnished  by  J.  D.  Hodgen. 


70 


THE  LABOJIATOIIY. 


understand  the  prfnci])le.s  underlying  its  construetion  sufliciently  well 
to  be  al)le  to  repair  it.     Repair  is  most  often   needed  in  the  niufHe; 


Fir:.  89 


The  Pelton  Furnace. 
Fig.  90 


Mitchell  furnace  No.  1.     (About  half-^ize.) 


therefore,  simplicity  of  construction  and  ease  of  repair  in  this  part  of 
the  furnace  are  most  essential.      The  following  is  a  description  of  a 


PORCELAIN  FURNACES. 


71 


very  simple  method  of  constnu'ting  an  electric  furnace  for  the  fusion  of 
porcelain.  With  such  an  aj)pliance  as  this,  heat  necessary  for  the  fusion 
of  the  most  refractory  bodies  can  be  quickly  obtained.  It  is  suitable 
for  use  on  a  110  volt  direct  current  circuit. 

Furnace  Case. — Any  rectangular  or  dome-top  ciist-brass,  gun-metal  or 
bronze  case,  2|  by  2|  by  3  inches  in  width,  depth,  and  length,  respectively, 
will  suffice  (Fig.  91).  The  front  end  of  the  case  should  be  provided 
with  an  opening  or  door  the  size  of  the  open  end  of  the  muffle  desired. 
For  instance,  for  crown,  bridge,  or  inlay  work,  it  need  not  have  an  area 
greater  than  1  square  inch.  Beneath  the  door  a  shelf  flush  with  the 
bottom  of  the  muffle  and  running  the  full  width  of  the  case  and  about 
1  inch  in  width  should  be  provided.  The  whole  case,  except  the  back, 
may  be  cast  in  one  piece,  if  desired,  as  there  is  no  occasion  for  removing 
any  of  the  enclosing  walls  except  the  back  end,  which  should  be  separate 

Fig.  91 


Dental  electric  furnace. 

and  secured  in  place  by  two  or  three  screws.  When  it  has  been  removed, 
the  muffle  may  be  adjusted,  repaired,  or  replaced  with  very  little  trouble. 
The  metal  portion  of  the  back  need  not  be  much  more  than  half  an 
inch  wide  (Fig.  92),  which  is  sufficient  to  hold  in  place  a  fire-clay  or 
soap-stone  insulating  refractory  end  piece  (Fig.  93)  which  fits  the  end 
of  the  interior  of  the  case,  and  through  which  the  platinum  wire  terminals 
are  conducted  and  properly  connected  outside  of  the  case.  A  complete 
furnace  of  this  character  is  shown  in  Fig.  91. 

The  furnace  case  may  be  supported  on  a  soap-stone,  marble,  or  other 
base,  4  by  5  by  I  inches,  by  four  metallic  posts  about  H  inches  long. 
Copper  wires  about  No.  14  gauge,  leading  to  the  buttons  and  switch, 
are  laid  in  grooves  cut  in  the  under  surface  of  the  base  (Fig.  95).  The 
furnace  is  devised  to  carry  a  muffle  in  which  a  portion  of  the  platinum 
wire  in  the  muffle  coil  is  cut  out  of  circuit  by  the  switch  below,  thus 
obviating  the  necessity  of  a  rheostat,  the  principle  of  which  arrangement 
will  be  explained  further  on. 


72 


THE  LABORATORY 


The  muffle  is  made  in  the  following  manner:  A  form  of  core  (Fig.  9(»), 
about  5  inches  in  length,  is  made  oi  .soft  wood,  tapering  very  .slightly 
from  end  to  end,  so  that  the  circumferential  measurement  is  sufficiently 
le.ss  at  one  end  than  the  other  to  admit  of  the  core  ])eing  withdrawn 
from  the  fini.shed  muffle  made  about  it  without  breaking  or  distorting 
the  fragile  case. 

The  form  is  first  covered  witli  two  ])ieces  of  smooth,  heavy  writing 


Fig.  92 


Fig.  93 


Metal  frame  flir  liack  'if  furiiaoe. 


Fire-clay  back  of  furuacc  :  A,  for 
exit  of  platinum  wire  terminals; 
B,  bindinqr  posts  for  copper  wires. 


Fig.  94 


Biuiliiig   post. 
Upside  down. 


Fig.    95 


paper  (Fig.  97),  each  piece  of  which  extends  nearly  around  the  form, 
the  ends  of  one  piece  overlapping  those  of  the  other,  and  lioth  held  in 
position  by  pins.  This  done,  the  form  is  ready  to  be  wound  with  the 
platinum  wire. 

About  16  feet  of  Xo.  '60  gauge,  pure,  perfect  platinum  wire  having 

been  provided  is  first  well  annealed,  pre- 
ferably in  an  electric  oven,  and  two  pieces 
of  not  more  than  6  inches  each  cut  off 
of  one  end,  thus  leaving  a  piece  of  wire 
about  b")  feet  in  length.  About  bS  inches 
from  the  first  end  of  the  long  piece  of 
wire*  one  of  the  6-inch  pieces  is  securely 
and  neatly  attached;  IS  inches  farther 
on  (.36  inches  from  the  end  of  the  long 
wire)  the  second  6-inch  piece  is  in  like 
manner  attached.  This  done,  the  wire 
for  the  muffle,  as  a  whole,  presents  four 
ends  and  is  ready  for  winding.  The  first 
end  of  the  long  wire  is  made  secure 
around  one  of  the  pins  on  the  small  end 
of  the  form  (Fig.  97),  leaving  about  6 
inches  as  a  terminal.  The  wire  is  wound 
about  the  form,  not  tightly,  but  firmly, 
so  as  to  keep  its  place,  with  coils  about 
a  millimetre  apart,  leaving  about  6  inches  of  the  last  end  of  the  long 
wire  unwound  and  drawn  under  the  last  coil  to  hold  it  .securely  and  to 
become  another  terminal  (Fig.  97). 


Bottom  of  the  base  showing  tlie  wiring. 


rORCKLA  L\  FlJIiyA  CKS. 


73 


A  mixture  of  fire-clay,  one  part,  and  oronnd  fire-l)rick,*  one  part,  is 
now  made  into  a  pasty  mass  with  water  and  thinly  painted  over  the 
Avire  on  the  foi-m  with  a  soft  brush.  This  is  dried  over  a  Bunsen  burner 
flame  and  another  eoat  added  and  dried  in  the  same  way,  and  so  on, 
until  the  muffle  is  about  j\  of  an  ineh  in  thickness.  The  whole  is  then 
dried  thoroughly.  Avoid  applying  the  mixture  too  thick  each  time  before 
drying,  or  the  muffle  will  crack  badly  and  these  cracl<s  will  be  difficult 

Fig.  96 


Wooden  form  for  making  muffle. 

to  fill,  ^\^len  the  muffle  is  made  sufficiently  thick  to  give  proper  rigiditv 
(Fig.  98)  and  well  dried,  carefully  withdraw  the  pins,  catch  the  muffle 
firmly  in  the  left  hand,  and  with  a  hammer  strike  the  small  end  of  the 
wooden  form  a  sharp  blow.  This  will  drive  the  form  out  of  the  muffle, 
after  which  the  papers  can  be  easily  removed.  The  muffle  now  presents 
the  appearance  of  Fig.  99,  with  the  four  end  wires  protruding  from  the 
clay  encasement.     A  thin  mixture  of  the  clay  and  fire-brick   can   now 

Fig.   97 


Form  with  paper  wrapper  and  wire  wound. 

be  taken  on  the  brush  and  painted  over  the  wire  coils  on  the  inside  of 
the  muffle,  so  as  to  barely  cover  them  and  fill  in  any  inequalities  of  the 
surface.  This  being  done  and  the  muffle  again  dried,  its  uneven  ends 
are  trimmed  smooth  and  the  wire  ends  laid  from  the  front  end  back 
along  the  muffle,  so  as  not  to  come  in  contact  with  each  other,  and  held 
in  the  desired  position  by  a  thread  tied  around  the  muffle  (Fig.  99). 
The  muffle  may  now  be  placed  in  position  in  the  furnace  case,  with  the 
front  end  as  nearly  flush  as  possible  with  the  door  of  the  case.  A  thick 
asbestos  board  should  be  placed  between  the  bottom  of  the  muffle  and 
the  floor  of  the  furnace  case  to  support  the  muffle,  and  asbestos  fibre 

"'  It  is  probably  better  to  secure  an  old  fire-brick  that  has  been  repeatedly  burned  in  use,  grind  it 
up,  not  too  finely,  and  pass  a  magnet  through  the  mass  to  abstract  any  iron  that  may  be  present. 
Silex,  i  hree  parts  and  fire-clay,  one  part  may  be  used,  but  the  old  fire-brick  is  considered  preferable 


74 


THE  LABORATORY. 


packed  uU  around  between  the  muffle  and  the  furnace  case  to  hold  the 
former  firmly  in  position.  Finally,  a  piece  of  asbestos  board  large  enough 
to  close  the  end  should  l)e  adjusted  over  the  back  end  of  the  muffle, 
and  the  four  end  wires  carried  around  the  asbestos  l)oard  and  threaded 
through  the  holes,  .1,  Fig.  1)3,  in  the  soap-stone  or  baked  clay  back, 
in  proper  order:  Thread  the  first  end  of  the  long  wire  through  hole  1, 
the  first  attached  6  inches  through  hole  2,  the  second  attached  6  inches 
through  hole  3,  then  the  second  end  of  the  long  wire  through  hole  4. 
The  soap-stone  or  baked  clay  l)ack  being  set  in  position,  the  end  casting 
of  the  furnace  case  may  be  secured  and  the  })latinum  end  wires  made 


Fio.   98 


Muffle  ready  to  be  removed  from  form. 

fast  to  the  under  end  screws  of  the  binding-posts,  C,  Fig.  94,  bearing 
the  same  number  on  the  soap-stone  or  clay  ])ack. 

A  copper  wire  (No.  14  gauge)  is  now  led  from  the  terminal  post,  A, 
Fig.  95,  along  a  groove  in  the  bottom  of  the  stone  base  of  the  furnace, 
to  the  binding-post  B,  which  carries  the  key  of  the  switch.  Another 
copper  wire  of  the  same  size  is  carried  from  binding-post  No.  1,  Fig.  93, 
of  the  baked  clay  back,  down  through  a  hole  in  the  l)ase.  No.  1,  Fig.  95, 
and  along  a  groove  to  binding-post  C,  which  forms  the  first  button  of 


Fig.  99 


Muffle  ready  to  be  set  in  furnace  case. 

the  switch.  Another  from  binding-post  No.  2,  Fig.  93,  down  and  along 
to  binding-post  D,  Fig.  95,  forming  the  second  button  of  the  switch. 
Another  from  binding-post  No.  3,  Fig.  93,  down  and  along  to  binding- 
post  E,  Fig.  95,  which  forms  the  diird  and  last  button  of  the  switcti. 
Still  another  copper  wire  of  the  same  size  is  carried  from  binding-post 
No.  4,  Fig.  93,  down  through  hole  No.  4  in  the  base.  Fig.  95,  to  binding 
post  F,  which  forms  a  terminal. 

These  wires  all  properly  adjusted,  the  furnace  may  be  connected  with 


PORCELALV  FURNACICS.  75 

tlie  current  (Fig.  9i),  and  the  key  of  the  switcli  placed  on  button  No.  1, 
for  a  few  seconds  at  a  time,  until  the  new  muffle  is  dried,  or,  better, 
leave  the  key  of  the  switch  on  button  No.  1  and  give  the  muffle  the 
current  from  the  connecting  wall  switch.  After  the  muffle  is  perfectly 
dry,  the  switch  key  may  be  moved  to  buttons  No.  2  and  No.  3,  thus 
raising  the  muffle  to  its  maximum  heat. 

The  rationale  of  this  method  of  wiring  is:  When  the  key  is  on  button 
No.  1,  the  current  is  carried  through  the  whole  wire  of  the  muffle  (about 
fourteen  feet)  and  is  too  little  to  perfectly  heat  this  amount  of  wire;  it 
is  changed  to  button  No.  2  and  passes  through  eighteen  inches  less  of 
wire  and  a  greater  heat  is  exliibited;  finally,  on  button  No.  3  the  current 
passes  through  eighteen  inches  less  (about  eleven  feet)  of  wire  and 
furnishes  somewhere  near  the  maximum  heat. 

Should  the  muffle  fail  at  any  time  to  heat  up,  the  failure  is  probably 
due  to  the  platinum  wire  having  been  broken  at  some  point.  If  this 
"burn-out"  occurs  in  the  first  eighteen  inches  of  the  coil,  the  furnace 
will  heat  up  from  the  second  button;  if  in  the  first  thirty-six  inches  of 
the  coil,  it  w\\\  heat  up  from  the  third  button ;  if  back  of  this,  the  furnace 
will  not  heat  up  at  all.  By  removing  the  muffle,  the  burn-out  may  be 
located.  Raise  the  broken  ends  out  of  the  clay  and  carefully  twist  them 
together,  using  no  metallic  instruments;  make  a  hole  in  the  clay  and 
press  the  ends  in  it,  then  cover  with  a  little  clay,  replace  the  muffle  and 
it  will  heat  up  as  before. 

After  considerable  use,  especially  at  the  maximum  heat,  the  platinum 
wire  in  the  mufile  seems  to  undergo  some  molecular  change,  perhaps 
a  crystallization,  which  prevents  its  exliibiting  as  great  a  heat  as  when 
first  placed  in  the  muffle.  It  is  then  more  economical  to  take  out  the 
old  muffle  and  substitute  a  new  one. 

The  proper  fusing  of  porcelain  is  an  operation  of  extreme  delicacy, 
and  requires  nice  precision  in  the  adjustment  of  the  temperature  and 
time  of  baking  which  is  necessary  for  each  kind  of  porcelain  used.  Too 
rapid  heating  causes  the  porcelain  to  crack  and  check,  while  overheating 
causes  generally  a  burning  out  of  the  color,  and  sometimes  a  porous 
condition  due  to  the  formation  of  gas  in  the  mass.  Underfused  porcelain 
is  darker  in  color,  and  not  so  translucent  as  that  which  is  properly 
baked,  and  it  is  usually  granular  on  the  surface.  If  the  porcelain  is 
brittle  after  it  is  fused,  this  probably  means  that  it  was  cooled  too  rapidly 
• — did  not  get  the  temper  of  slow  cooling.  If  it  shows  a  pale  bluish-white 
color  with  its  porcelain  filled  with  bubbles,  this  indicates  "gasing,"  or 
contact  with  some  of  the  products  of  combustion  through  a  leaking  muffle. 

In  using  the  older  furnaces  the  workman  had  to  depend  solely  upon 
visual  judgment  in  determining  when  the  porcelain  was  properly  fused. 
Some  made  use  of  a  pellet  of  pure  gold,  in  working  with  the  high-fusing 
bodies,  placing  it  in  the  muffle  and  keeping  the  piece  of  work  in  the 
heat  a  definite  time  after  the  gold  was  seen  to  fuse  (2012°  F.).  This 
principle  is  utilized  by  Le  Cron  in  his  pyrometer,  in  which  by  var}ing 
the  proportions  of  gold  and  platinum  in  the  pellet  the  temperature  of 
any  given  one  of  the  high-fusing  bodies  may  be  judged,  and,  having 
been  determined,  the  body  may  be  baked  at  that  temperature. 


70 


THK  LABORATORY. 


To  Dr.  \V.  A.  Price,'  of  Cleveland,  Ohio,  l)eloiigs  tlie  credit  of  placing 
the  first  dental  pyrometer  on  the  market.  The  pyrometer  designed  by 
Dr.  Price  depends  upon  the  principle  of  the  thermopile.  When  certain 
metals  in  contact  are  subjected  to  heat  an  electric  current  is  generated, 
the  quantity  of  which  depends  upon  the  temperature  to  which  these 
metals  are  subjected,  increase  in  the  temperature  causing  a  corresponding 
increase  in  the  quantity  of  current  given  off.  A  small  pellet  of  the  metal 
rhodium  is  welded  to  two  ])latinum  wires,  and  one  or  more  of  these 
miniature  thermopiles  are  introduced  in  the  rear  of  the  muffle,  ^^hen 
they  are  heated  a  feeble  current  is  generated.  As  the  temperature 
increases  the  quantity  of  current  in  a  like  manner  increa.ses  and  this 
is  measured  by  means  of  a  delicate  milammeter. 

The  pvrometer  designed  by  N.  K.  Garhart,  of  Indianapolis,  Indiana, 
depends  upon  an  entirely  different  principle.  lie  interposes  in  the 
current  of  a  low  voltage  circuit  a  "  Xernst  Glower,"  and  measures  the 


Fig.  100 


Price  furnace  and  pyrometer. 


quantity  of  current  passing  through  the  "  glower"  by  means  of  a  delicate 
milamnieter.  The  "  Xernst  Glower  "  is  a  peculiar  variety  of  porcelain 
which  is  a  non-conductor  when  cold,  but  a  conductor  when  heated. 
The  conductivity  of  the  "glower"  is  in  ratio  to  the  increased  temper- 
ature of  the  muffle.  The  amount  of  current  reciuircd  for  the  "  gloAver" 
undergoes  no  change  from  its  repeated  use.  The  current  is  obtained 
from  the  street  circuit  on  the  shunt  plan,  and  owing  to  the  minute  amount 
required  for  this  purpose  slight  fluctuations  of  the  street  supply  current 
do  not  in  any  way  impair  the  accuracy  of  the  instrument. 

Lathes.— For  grinding  and  fitting  'teeth   a  light,  easy-running  lathe, 

1  J.  Q.  Byrarn,  The  International  Dental  Journal,  vol.  xxvi,  p.  509. 


LA  THES. 


77 


with  a  substantial  frame  of  iron  or  wood  2  feet  1 1  inches  higli  to  the 
centre  of  the  pulley  head,  which  will  permit  the  operator  to  sit  while  at 
work,  should  be  provided.  The  sitting  position  saves  him  from  much 
of  the  fatigue  occasioned  by  continuous  work  of  this  kind,  while  it 
affords  the  steadiness  to  the  body  and  hands  which  is  demanded  by 
the  delicate  and  precise  work  of  fitting  teeth  to  gold  or  silver  plates  and 
to  each  other. 

The  centre  of  the  pulley  head  should  be  not  less  than  4  inches  from 
the  top  of  the  lathe  table,  which  should  be  formed  of  ash  or  cherry 
wood  26  inches  long  by  20  inches  wide  and  If  inches  thick.  The  frame 
may  be  made  of  oak  or  ash  wood  securely  fastened  together,  or  a  lathe 


Fig.  101 


L  iiique  lathf-lieitd. 

table  similar  to  the  one  in  Fig.  102  may  be  used.  It  occupies  Ktde 
space,  is  provided  with  two  drawers  to  hold  the  grinding  wheels  and 
polishing  powder  carriers,  and  has  a  middle  drawer  lined  with  galvan- 
ized iron  which  catches  the  waste  from  the  lathe  through  the  opening 
in  the  top  of  the  table. 

Many  of  the  lathes  offered  for  sale  at  the  dental  depots  are  not 
entirely  satisfactory  either  for  fitting  teeth  or  polishing.  Their  driving 
wheels  are  either  too  heavy  or  too  light.  Figs.  101  and  102  illustrate  a 
lathe-head  and  driving  wheel  of  recent  introduction,  which  will  doubtless 
answer  all  requirements  of  the  dental  laboratory.  Fig.  103  shows  a 
sectional  view  of  the  lathe-head;  Fig.  104,  a  set  of  chucks  for  mounting 
corundum  wheels  and  polishing  brushes,  etc.;  Fig.  105,  a  reamer  for 
fitting  wheels  having  wooden  centres  to  taper  screw-chucks. 

A  lathe  intended  for  fitting  teeth  does  not  require  great  speed  or 
much  power.  A  good  lathe  may  be  made  by  obtaining  the  frame  and 
driving  wheel  of  one  of  the  inexpensive  forms  of  amateur  turning  lathes 
now  in  the  market^  and  adjusting  a  Lawrence  head  to  it.     The  working 


78 


THE  LABORATORY. 


parts  of  the  lathe  should  he  kept  clean,  well  oiled,  and  j)rote(ted  as  far 
as  possible  from  abrading  powders  and  other  gritty  ])artieles  with  which 
it  is  constantly  surrounded.     In  perhaps  the  majority  of  dental  labora- 


Fio.  102 


Lathe  table  and  driving  wheel. 


tories  but  one  lathe  is  used  for  all  purposes  of  grinding  and  polishing.  It 
is  much  l)etter,  however,  to  have  a  larger  and  stronger  lathe  for  ])olish- 
ing  purposes  exclusively,  and,  as  greater  speed  is  required  for  this  pur- 


FiG.  103 


Section  through  unicivie  lathe-head. 


pose,  it  should  be  about  3  feet  10  inches  in  height  to  the  centre  of  the 
pulley  head,  so  that  the  operator  may  stand  while  using  it;  the  form  of 
lathe  head  shown  by  Fig.  107  will  answer  admirably.     The  fly-wheel 


LA  THES. 


70 


should  be  at  least  20  inches  in  diameter,  and  should  weigh  about  35 
pounds.  The  treadle  should  be  operated  by  a  lever  (jr  leg  motion,  and 
not  by  what  is  known  as  the  heel-and-toe  treadle,  which  does  not  afford 


Fig.  104 


Chucks  for  unique  lathe-head. 


sufficient  speed  or  power.     The  lift  of  the  treadle  should  be  not  less 
than  2J  inches. 

One  of  the  most  valuable  applications  of  electricity  to  the  needs  of 
the  dentist  is  in  the  running  of  laboratory  lathes,  and,  when  supplied 
with  the  110-volt  direct  current,  such  an  apparatus  is  by  far  the  most 
convenient  and  effective  lathe  used  for  the  purpose  of  fitting  teeth  or 


Fig.  105 


Reamer  for  brush-wheels. 


polishing  dentures.  In  the  last  few^  years  thoroughly  satisfactory  lathes 
have  been  manufactured  also  for  the  alternating  current,  but  the  direct 
current  is  preferable  as  a  source  of  power. 

As  showm  by  Fig.  106,  we  have  an  electric  lathe  w^hich  is  admirably 
adapted  to  either  general  laboratory  uses  or  as  an  office  lathe  for  the 


80 


THE  LABORATORY. 


fitting  of  porcelain  crowns  or  tlie  adjustment  of  the  articulation  of  arti- 
ficial dentures.  Its  bearings  are  completely  protected  from  dust  by  the 
japanned  iron  jacket  which  covers  the  armature.  It  is  noiseless,  and  is 
constructed  with  such  precision  that  its  motion  is  hardly  perceptible.  It 
is  adapted  for  the  110-volt  current,  and  the  author  has  found  that  it 
possesses  more  than  sufficient  power  for  all  puq^oses  recjuired  by  the 
dentist.  As  no  special  table  is  required  for  this  motor,  it  may  be  placed 
in  any  convenient  position.      It  may  be  run  in  cither  direction. 


I'lG.  lUti. 


**> 


y.  S.  White  electric  lathe. 


It  has  a  range  of  speed  varying  from  1000  to  4000  revolutions  per 
minute,  and  the  torque,  or  pull,  is  as  great  at  the  lowest  speed  as  at  the 
highest. 

The  regulation  of  .speed  and  the  starting  and  stopping  of  the  lathe 
are  effected  by  a  slight  turn  of  the  milled  stud  .shown  in  the  cut.  The 
chucks  are  fixed  on  the  tapered  ends  of  the  .spindle  by  a  light  tap,  with 
any  metal  tool  which  may  be  conveniently  at  hand,  and  can  be  instantly 
removed  while  revolving  or  stationary  by  the  tool  shown  below  the  chucks, 
used  as  a  lever  to  force  the  chuck  off  the  end  of  the  .spindle. 

The  polishing  lathe  should  be  provided  with  a  drawer  for  the  safe 
keeping  of  mandrels,  brush  wheels,  felt  and  cotton  wheels,  cones,  etc., 
together  with  the  abrading  and  polishing  powders  which  are  usually 
employed  in  the  final  finishing  of  the  ditterent  kinds  of  prosthetic  pieces. 
Corundum  wheels,  spatulas,  cements,  etc.,  used  in  fitting  and  attaching 
teeth  to  the  plate,  should  be  kept  in  a  drawer  attached  to  the  grinding 
and  fitting  lathe. 

The  corundum  wheels  so  extensively  used  in  the  dental  laboratory 
are  made  of  the  mineral  corundum  found  in  Ceylon  and  in  Pennsylvania, 
Georgia,  Massachusetts,  and  North  Carolina.  It  occurs  in  crystals  of  the 
form  of  double  six-sided  pyramids  of  various  sizes,  and  in  some  localities 
in  large  masses  without  crystalline  form.  Corundum  is  an  aluminum 
oxide  haA^ng  the  formula  AljOg.    The  ruby  and  sapphire  are  transparent 


LA  TIIES. 


81 


varieties  of  this  mineral,  their  eolor  being  (hie  to  the  presence  of  a 
small  amount   of  coloring  oxides.     Emery,  the  use  of  which  preceded 


Fk;.  107 


Lathe-head  suitable  for  polishing  lathe. 


corundum  as  an  abrasive  agent  in  the  dental  laboratory,  is  a  coarse 
variety  of  corundum.  Corundum  is,  with  the  single  exception  of  the 
diamond,  the  hardest  mineral  known.  It  is  prepared  by  pulverizing  the 
crystals  in  an  iron  mortar  by  successive  blows  of  a  heavy  steel  pestle. 
The  three  grits  which  are  employed  in  making  wheels  for  dental  pur- 
poses are  obtained  by  passing  the  powdered  corundum  through  sieves  of 
different  degrees  of  fineness;  they  are  known  as  fine,  medium,  and 
coarse.  The  latter  will  cut  most  rapidly;  the  finest  will  not  cut  so  fast, 
but  will  leave  a  mucli  finer  surface.  The  powdered  corundum  is  mixed 
with  finely  ground  gum  shellac  in  the  proportions  of  3  ounces  of  corun- 
dum to  1  of  shellac;  this  is  carefully  heated  and  thoroughly  mixed  until 
it  becomes  of  a  doughy  consistence,  when  it  is  put  into  an  iron  mold 
made  in  two  parts,  previously  oiled.  This  mold  is  placed  in  a  small 
press  and  force  enough  applied  to  consolidate  and  distribute  the  mixture 
into  all  parts  of  the  mold.  Too  much  force  should  be  avoided,  as  it  is 
liable  to  drive  out  so  much  of  the  shellac  that  the  particles  of  corundum 
will  not  be  sufficiently  adherent— a  condition  which  will  greatly  lessen  the 
wearing  qualities  of  the  wheel.  After  the  wheel  has  been  removed  from 
the  mold,  which  is  done  by  tapping  the  latter  sharply  with  a  wooden 
mallet,  it  is  washed  in  alcohol  for  the  purpose  of  removing  the  shellac 
from  the  surface  and  leaving  the  wheel  in  a  sharp  or  gritty  condition. 

Carborundum  wheels,  which  are  also  in  general  use  for  grinding 
purposes,  have  as  their  abrasive  constituent  "carborundum,"  or  the 
carbide  of  silicon.  This  substance  was  made  experimentally  in  1893 
by  Mr.  G.  E.  Acheson,  and  is  now  manufactured  on  an  exiensive  scale 
at  Niagara  Falls,  where  large  amounts  of  electricity  are  economically 
available,  the  intense  heat  of  the  electric  furnace  being  necessary  to 
6 


82 


THE  LABORATORY. 


% 


■.J? 


produce  the  combination  of  the  carbon  and  sihcon.  Carbon  in  the  form 
of  finely  divided  coke,  silica  as  very  pure  and  clean  sand,  common  salt 
(NaCl),  and  sawdust  mixed  together  in  definite  proportions  constitute 
the  charge  for  the  furnace.  This  is  built  of  brick  about  IG  feet 
long  by  ()  feet  wide  and  4  feet  high.  It  is  packed  with  the  charge  up 
to  the  level  of  the  electrodes,  which  enter  it  about  the  centre  of  each 
end,  and  a  core  of  crushed  coke  is  laid  from  one  elec- 
^^"-  '  '"^  trode  to  the  other.     The  remainder  of  the  charge  is 

then  put  in  and  piled  up  to  a  height  of  about  8 
f(>et.  The  current  is  then  turned  on.  About  1000 
horse-power  of  energy  is  utilized  at  an  average 
voltage  of  185,  and  a  temperature  approximating 
7500°  F.  is  reached.  The  burning  takes  thirty-six 
hours,  the  sawdust  burning  out  and  rendering  the 
mass  porous  for  the  escape  of  carbon  monoxide  and 
other  gaseous  products.  A  mass  of  crystals  is  formed 
around  the  core,  which  consists  of  carbide  of  silicon 
(CSi),  the  carbon  and  silicon  having  combined  in 
atomic  proportions.  These  crystals  are  crushed, 
treated  to  a  bath  of  dilute  sulphuric  acid,  washed, 
and  sieved.  The  wheels  are  made  of  the  various 
sizes  of  crystals  mixed  with  feldspar  and  kaolin, 
which  constitute  the  "bond."  They  are  molded 
into  shape  under  tremendous  pressure  and  baked  in 
a  kiln  for  seven  days.  Carborundum  is  harder  than 
corundum  and  is  more  brittle.  AMieels  made  of  it 
may  be  run  as  well  wet  as  dry  and  will  not  clog. 
They  do,  however,  wear  unevenly,  probably  due  to 
lack  of  homogeneity  of  the  bond  or  its  uneven  baking. 
Frecjuent  tooling  with  the  dresser  shown  in  Fig.  108 
will  keep  them  true. 

While  grinding  porcelain  teeth  the  corundum  wheel 
must  be  kept  constantly  wet  to  prevent  the  shellac 
from  becoming  heated  by  friction — a  condition  which 
instantly  impairs  its  cutting  properties.  Numerous 
appliances  have  been  devised  in  the  form  of  "drip 
cups,"  designed  to  automatically  sup]>ly  sufficient 
water  to  the  w^heel  while  in  use  to  prevent  heating; 
but  these  are  objectionable  in  more  than  one  respect, 
and  are  liable  to  obstruct  the  light  and  prevent  it 
from  directly  falling  upon  the  point  of  contact  of 
the  tooth  with  the  wheel.  A  simple  dish,  oblong 
in  form,  with  the  dimensions  of  8  inches  in  length 
by  5  inches  wide,  by  2\  in  depth,  partially  filled 
serves  as  a  good  hand-rest,  while  a  piece  of  sponge 
of  the  size  of  a  large  walnut,  which  the  operator  will  soon  accjuire  the 
habit  of  holding  between  the  index  and  middle  finger  of  the  right  hand 
Avhile  he  keeps  it  in  contact  with  the  corundum  wheel,  is  an  excellent 
means  of  conveying  water  to  the  wheel  and  preventing  it  from  splash- 
ing his  face  or  clothing. 


Dreiser  for  render- 
ing worn  oarborundum 
wheels  true. 

with  clean  water, 


LATHES.  83 

There  are  at  least  seven  sizes  of  coninduin  wheels  made  for  dental 
laboratory  purposes,  ranging  from  f  of  an  ineh  in  diameter  to  3|-  inches, 
but  the  author  has  found,  after  much  experience  in  fitting  carved  blocks, 
rubber  sections,  and  single-gum  teeth,  that  a  maxinunn  of  1  inch  in 
diameter  and  I  of  an  inch  in  thickness  is  (juite  large  enough  for  joint- 
ing piu"poses,  while  the  smaller  sizes,  which  are  indispensable,  are 
obtained  by  the  wearing  away  of  the  1-inch  v^heels. 

In  finishing  dentures  the  first  step  is  the  proper  levelling  of  the  surface; 
this  is  usually  done  in  metallic  cases  with  the  corundum  wheel,  after 
which  the  scratches  left  by  the  sharp  particles  of  corundum  should 
be  removed  by  a  keen-edged  vulcanite  scraper.  The  piece  is  then  ready 
for  the  "Scotch  stone,"  a  soft  mottled  stone  much  used  by  silversmiths 
and  workers  in  the  precious  metals,  furnished  by  the  dental-supply 
houses  in  pieces  of  6  inches  in  length  by  j  inch  in  thickness.  This 
material  has  decided  abrasive  qualities,  and  is  used  chiefly  to  remove  the 
scratches  left  by  the  corundum  wheel  and  scraper;  it  produces  a  fine 
silk-like  surface  and  brings  the  case  to  the  point  where  the  buff  wheels 
armed  with  the  coarser  powders,  such  as  pumice,  are  to  be  used;  these 
produce  a  surface  which  may  be  highly  polished  by  the  brushes  which 
should  follow  the  buff  wheels,  and  should  carry  the  finer  polishing 
powders  or  those  used  for  the  purpose  of  obtaining  high  lustre,  such  as 
calcined  buckhorn  when  the  case  is  of  gold  or  silver,  and  prepared  chalk 
when  it  is  of  vulcanite  or  celluloid. 

In  vulcanite  or  celluloid  work  the  corundum  wheel  need  not  be  used, 
the  scraper  being  sufficient  for  the  levelling  of  the  surface,  after  which 
the  finer  numbers  of  emery  paper,  Nos.  0  and  h,  are  employed,  until  all 
traces  of  the  scraper  are  removed,  when  it  is  ready  for  the  pumice  powder, 
which  is  generally  applied  with  a  small  stick  of  soft  wood,  such  as  poplar 
or  pine,  after  v/hich  the  denture  is  ready  for  the  felt  or  other  kind  of 
buff  wheel  and  fine  pumice. 

Buff  wheels  and  cones  are  made  of  felt,  cotton,  duck,  leather,  soft 
wood,  cork,  disks  of  cloth  or  chamois  leather,  stitched  together,  etc. 
Felt  is  probably  the  best  of  the  various  materials  used  in  forming  buff 
wheels;  these  wheels  can  be  obtained  at  the  dental  depots  in  sizes 
ranging  from  1^  to  2h  inches  in  diameter.  Buff  wheels  are  intended  to 
cut  and  not  to  polish.  They  are 
usually  armed  with  pumice,  and 
must  be  kept  constantly  wet  while 
in  use.  The  best  size  of  buff  wheel 
for  dental-laboratory  use  is  If  inches 
in  diameter  by  f  of  an  inch  in  thick-  Felt  wheei-chuck. 

ness.      Smaller  sizes  are  obtained 

by  the  wearing  away  of  the  larger  wheels.  They  are  easily  mounted 
upon  the  "screw-cone"  mandrel,  to  which  they  do  not  ordinarily  require 
to  be  cemented  or  shellacked.  An  ingenious  felt  wheel-chuck  has 
been  suggested  by  Dr.  F.  E.  Pomroy;  it  is  provided  with  three  steel 
pins  to  prevent  the  wheel  from  revolving  on  the  screw  (Fig.   109). 

The  brush  wheel  is  employed  for  the  purpose  of  obtaining  a  still  finer 
surface  than  is  attainable  with  the  Scotch  stone  or  buff  wheel  and  for 


84 


THE  LABORATORY. 


the  final  polishing.    There  is  ciuite  a  variety  of  forms  made  for  dental 
laboratory  use,  beginning  with  the  wood-centre  brush  wheel  with  straight 


Fig.  110 


JS-J-S 


Brush  wheel. 


bristles  in  from  one  to  four  rows  (Fig.  110);  the  brush  wheel  with  con- 
verging bristles  (Fig.  Ill);  the  cup-shaped  wheel  with  from  one  to  four 


Brush  wheel  ;  converging  bristles. 


rows  of  brisdes  (Fig.  112);  cup-shaped  brisdes  with  long  wooden  shanks; 
hub-shaped    with    straight   bristles   and    hub-shaped    with    converging 


Fin    112 


.x-»<V 


Cup-shaped  lirush  wheel. 


bristles,  etc.     In  selecting  brushes  it  should  be  remembered  that  those 
with  coarse  bristles  are  to  be  employed  with  abrading  powders  of  the 


FINISHING  POWDERS. 


85 


class  to  which  pumice  belongs,  while  those  with  soft  bristles  are  particu- 
larly adapted  for  use  with  prepared  chalk,  rouge,  calcined  buckhorn,  etc., 
or  wherever  a  high  lustre  is  to  be  attained.  Two  bruslies  of  each  of  the 
Nos.  1,  2,  and  3,  one  coarse  and  the  other  soft,  with  three  rows  of  bristles, 
are  sufficient  for  finishing  entire  or  partial  dentures,  with  the  addition  of 
two  small  straight  brush  wheels  of  l^  inches  in  diameter,  with  two  rows 
of  bristles,  for  finishing  places  in  the  denture  which  will  be  found  inac- 
cessible to  the  larger  wheels  and  for  polishing  crown  and  bridge-work. 
A  wood-centre  cotton  wheel  is  a  very  efficient  carrier  for  the  polishing 
powders  in  the  last  stage  of  finishing  (Fig.  113). 


Fk:.  113 


Cotton  wheel. 


Finishing  Powders. — Finishing  powders  are  di^^ded  into  two  classes, 
used  under  different  conditions  and  serving  different  purposes.  The 
following  partial  list  gives  a  few  of  those  in  general  use: 


Cutting  powders 


Polishing  powders 


f  Pumice, 

Emery, 

Corundum  flour, 

Arkansas  powder, 

Hindostan-stone  powder, 
L  TripoU, 

Calcined  buckhorn, 

Rotten  stone, 

Prepared  chalk. 

Rouge, 


used  with  a  lubricant 


}  used  comparatively  drj\ 


Emery  with  oil  has  long  been  used  by  workers  in  the  precious  metals 
for  cutting  dowm  the  surface  of  gold  and  silver  preparatory  to  the  final 
polishing,  but,  as  it  is  nearly  black'  and  liable  to  discolor  the  joints  of 
the  teeth,  it  is  an  objectionable  mixture  to  employ  in  the  finishing  of 


HO  nil:  LMionATonY. 

artificial  (leiiturcs;  hence  its  ])!ace  has  ahnost  entirely  been  taken  by 
pumice  powder,  with  Castile  soap  and  water  as  the  lubricant.  Emery  is 
perhaps  better  suited  for  finishing  continuous-gum  cases,  which,  having 
no  joints,  are  not  liable  to  the  same  danger  of  discoloration  as  are 
dentures  formed  of  single-gum  teeth;  platinum,  of  which  the  })lates  of 
tliis  kind  of  dentures  are  made,  resists  attrition  to  a  greater  extent  than 
does  gold  or  silver;  it  therefore  recjuires  a  more  decidedly  abrasive  powder 
than  would  suffice  for  either  of  those  metals  to  produce  smoothness 
enough  for  the  final  polishing. 

Of  the  polishing  powders  properly  so  called,  calcined  l)Uckhorn  has 
been  foimd  of  so  much  value  as  an  agent  in  the  production  of  high 
lustre  in  gold  and  silver  work  that  it  has  almost  entirely  superseded  the 
use  of  the  burnisher.  It  is  applied  with  a  soft-bristle  brush  wheel, 
similar  to  Fig.  113,  revolving  at  the  highest  speed  attainable.  The  pow- 
der is  at  first  slightly  moistened  with  water,  but  as  the  lustre  appears  it 
is  taken  up  between  the  tips  of  the  fingers  and  dropped  in  a  perfectly 
dry  condition  upon  the  plate. 

Rotten  stone  Is  also  an  excellent  polishing  powder,  but,  like  emery,  it 
is  liable  to  discolor  the  joints  and  to  find  its  way  behind  the  backings  in 
soldered  w^ork,  and  efl^ect  more  or  less  change  in  the  color  of  the  teeth. 
It  has,  therefore,  nearly  gone  out  of  use  as  a  polishing  material  in  the 
dental  laboratory. 

Prepared  chalk  is  as  efi'ective  an  agent  m  polishing  vulcanite  and 
celluloid  work  as  buckhorn  is  with  the  precious  metals.  It  is  also  applied 
mixed  sparingly,  at  first,  witli  water,  or  preferably  alcohol,  on  a  No.  3 
soft-bristle  brush  wheel  until  a  high  polish  begins  to  appear,  when  it  is 
dropped  in  a  quite  dry  state  upon  the  plate  while  in  contact  with  the 
rapidly  revolving  brush  wheel. 

There  is  always  some  danger  of  heating  vulcanite  plates  if  held  with 
force  against  a  rapidly  revolving  brush  wheel;  the  frequent  unaccount- 
able warping  of  vidcanite  dentures  may  possil^ly  be  due  to  this  cause; 
such  an  accident,  however,  need  not  occur  if  ordinary  care  is  observed 
in  allowing  merely  the  ends  of  the  bristles  to  come  lightly  in  contact 
with  the  plate. 

Rouge  is  a  valuable  polishing  powder  for  gold  and  silver,  and  is  much 
used  by  jewellers.  It  is  moistened  with  alcohol  and  applied  sparingly 
to  a  cotton  buff  wheel  running  at  high  speed.  Care  should  be  taken 
to  keep  it  from  the  joints  in  single-gmn  teeth  dentures,  as  its  removal 
is  a  matter  of  some  difficulty.  Calcined  buckhorn  has  to  a  considerable 
extent  supersed  d  It  on  account  of  Its  greater  cleanliness. 

The  use  of  the  burnisher  as  a  means  of  obtainino'  hl";h  lustre  in 
metallic  dentures  has  been  almost  entirely  abandoned,  because  of  its 
tendency  to  spring  or  warp  metallic  objects  to  which  It  Is  applied,  and 
of  the  fact  that  It  Is  unnecessary. 

Adhesive  Wax. — Rosln-and-wax  cement,  as  it  is  sometimes  called — 
which  Is  used  for  the  purpose  of  uniting  parts  of  work  preparatory  to 
its  investment  for  soldering,  such,  for  instance,  as  a  clasp  to  a  plate 
when  it  is  necessary  to  maintain  the  precise  relation  of  one  to  the  other 


FLUXED    WAX.  87 

until  pcrniaiUMitly  fixed  l)y  soldering,  and  for  temporarily  fastening  teeth 
to  plates  while  arranging  and  adjusting  tliem  to  the  mouth — is  an  indis- 
pensable adjunet  to  the  dentist's  work-beneh  and  lathe.  Adhesive  wax 
is  usually  composed  of  rosin  3  ounces,  wax  1  ounce.  The  proportions 
vary  with  the  season,  the  quantity  of  wax  being  reduced  to  half  an  ounce 
for  use  in  hot  weather  or  when  the  "cement"  is  found  to  be  too  ])lastic 
and  yielding  for  satisfactory  use.  Mastic  and  dammar  are  also  occasion- 
ally added  to  the  abo\'e  formula  for  the  purpose  of  stiffening  the  wax.  To 
prepare  the  cement,  melt  the  rosin  and  wax  in  a  suitable  vessel,  and  stir 
until  the  two  are  thoroughly  mixed;  test  pieces  should  be  drawn  out 
into  sticlcs  and  allowed  to  chill,  when,  if  found  to  be  but  slightly  brittle 
and  of  sufficient  toughness  to  hold  a  porcelain  tooth  or  clasp  in  their 
correct  relation  to  the  plate  while  being  removed  from  the  plaster  cast, 
the  cement  may  be  poured  into  a  vessel  of  cold  water,  and  when  cool 
enough  to  handle,  but  still  somewhat  plastic,  it  is  to  be  worked  into 
sticl«  of  about  the  size  of  an  ordinary  lead-pencil.  These  are  allowed 
to  become  quite  cold,  dusted  with  dry  plaster  to  prevent  them  from 
adhering,  and  laid  away  in  a  box  for  future  use. 

Rosin-and-wax  cement  is  greatly  improved  by  age;  it  is  therefore  a 
good  plan  to  keep  on  hand  a  considerable  quantity  of  it.  Shellac  rolled 
into  rods  and  sealing-wax  are  often  of  value  when  used  to  reinforce  the 
adhesive  wax  when  temporarily  attaching  teeth  and  clasps  to  plates 
previous  to  investing  for  soldering.  If  the  cement  shows  the  slightest 
tendency  to  yield,  a  small  quantity  of  shellac  or  sealing  wax  dropped 
upon  it  will  so  stiffen  it  that  the  denture  may  be  removed  from  the 
cast  without  change  of  relation  between  the  plate  and  the  clasps  or 
teeth. 

Fluxed  Wax. — ^This  preparation,  suggested  by  Dr.  Parr  for  attaching 
clamps  and  teeth  in  plate  and  bridge-work,  is  put  up  in  boxes  and  is 
applied  with  a  hot  spatula.  It  is  said  to  set  quickly  and  to  hold  the 
teeth  and  clasps  firmly  for  trial  in  the  mouth  and  during  subsequent 
soldering.  The  "cement"  throughout  which  the  flux  is  distributed  is 
readily  burned  or  melted  out,  leaving  the  flux  (probably  finely  powdered 
glass  of  borax)  as  a  deposit  over  the  crevices  and  surfaces  to  be  joined, 
ready  to  perform  its  oflBce  in  soldering.  Experts  in  crown  and  bridge 
work  seem  to  prefer  to  use  the  rosin-and-wax  cement  in  bulk,  from 
which  it  is  taken  up  and  applied  with  a  hot  spatula. 

Sticks  of  plain  wax  are  also  very  useful  in  "waxing  up"  vulcanite 
and  celluloid  cases;  these  may  be  made  of  the  waste  wax  which  is 
always  found  in  plentiful  quantity  about  the  office  and  lalioratory. 

Sheet  wax  plays  an  important  part  in  the  preparation  of  artificial 
dentures  on  bases  of  fusible  alloys,  vulcanite,  and  celluloid,  and  for  addi- 
tions and  modifications  of  the  plaster  cast  preparatory  to  molding  for 
the  zinc  die.  The  ordinary  base  plate  supplied  by  the  dental  depots  is 
generally  too  thick  for  the  temporary  plate  of  either  of  the  cast  or  plastic 
bases.  It  may  be  safely  said  that  much  of  the  uncertainty  of  dental 
laboratory  manipulations  with  these  materials  is  due  to  a  want  of  care 
in  the  preliminary  arrangement  of  the  wax.     For  some  unaccountable 


•"^H  THE  LABORATORY. 

reason,  the  majority  of  mechanical  dentists  seem  to  think,  it  necessary  to 
make  the  wax  plate  two  or  three  times  as  thick  as  the  denture  should  l>e 
when  finished,  and  after  the  vulcanizing);  to  reduce  it  to  the  proper  thick- 
ness with  steel  burs  sold  for  the  j)urpos(%  and  which,  on  account  of  the 
danojer  when  they  are  used  of  cuttinj^  through  the  plate,  should  have  no 
place  in  the  dental  laboratory.  The  preliminary  waxing  of  dentures  of 
this  class  should  be  done  with  such  care  and  ])recision  that  the  waxed 
piece  will  represent  not  only  the  exact  thickness  of  the  plate  when 
finished,  but  all  the  irregularities  of  surface  which  are  found  on  the  plaster 
cast.  The  rugae  and  other  prominences  of  the  mouth  assist  in  enunci- 
ation and  mastication,  and  should  l)e  represented  in  the  plate.  It  is 
probable  that  when  so  arranged  artificial  dentures  feel  less  like  foreign 
objects  when  worn  in  the  mouth.  In  order  not  to  obliterate  these  natural 
irregidarities  of  surface  the  waxing  may  be  done  with  two  or  three  layers 
of  wax,  not  much  thicker  than  is  used  in  making  artificial  flowers,  laid 
on  separately  and  pressed  with  the  thimib,  after  being  slightly  softened 
in  the  flame  of  a  spirit  lamp  or  Bunsen  burner,  until  in  complete  contact 
with  the  palatal  portion  of  the  cast.  Any  desired  thickness  can  be 
ol)tained  by  additional  sheets  of  wax,  but  the  main  point  to  be  gained 
by  this  method  of  waxing  is  uniformity  of  thickness:  and  if  the  waxing 
is  artistically  done,  little  or  no  scraping  or  finishing  will  be  needed  after 
vulcanizing  except  at  the  edges.  Indeed,  the  most  skilful  workers  in 
the  plastic  bases  have  demonstrated  that  the  best  results  in  vulcanite 
and  celluloid  work  are  obtained  by  precision  in  waxing  and  the  use  of  tin 
to  prevent  contact  with  the  plaster  of  the  investment,  and  to  afford  a 
polished  surface  which  shall  need  but  little  alteration  by  the  scraper. 
Sheet  wax  should  not  be  over  -^^  inch  in  thickness;  it  may  be  prepared 
by  dipping  a  square  piece  of  plate  glass  or  hard  wood  |  inch  thick, 
previously  oiled,  into  melted  wax,  allowing  it  to  cool  upon  the  slab, 
and  repeating  the  dipping  until  the  desired  thickness  is  attained,  after 
which  it  is  stripped  off,  trimmed  to  the  dimensions  of  3  inches  s(|uare, 
laid  in  a  box  with  tissue  paper  between  the  sheets,  and  it  is  then  ready  for 
use. 

Bench  Tools,  etc. — The  special  application  of  tools  will  be  found  in 
the  respective  chapters  devoted  to  the  particular  kinds  of  work  in  which 
each  is  used.  Our  remarks  here  will,  therefore,  be  confined  to  their  care 
and  proper  use.  There  are  two  infallible  indications  of  the  amount  of 
training  and  skill  possessed  by  a  mechanical  dentist :  (1)  the  condition 
of  his  tools;  (2)  the  state  of  the  cast  after  he  has  made  a  denture  upon 
it.  Skilful  and  accurate  workmen  will  do  so  little  damage  to  plaster 
casts  while  constructing  plates  or  clasps  that  little  or  no  evidence  of  their 
having  been  used  will  be  apparent  after  the  work  is  finished,  showing 
that  the  tools  have  been  well  selected,  kept  in  good  working  order,  and 
correctly  applied.  Tools  used  in  work  at  the  bench  may  l^e  ke})t  in  racks 
at  the  back  of  the  bench  top,  the  most  convenient  location  for  those  in 
frequent  senice,  or  they  may  be  kept  in  drawers  at  the  workman's  right 
hand  (Figs.  7,  8),  especially  if  they  are  not  often  needed.  Each  should  be 
provided  with  a  definite  place,  so  that  it  may  be  easily  found  when  the 
occasion  demanding  its  use  arises.     Cutting  tools,  as  gravers,  chisels, 


BENCH  TOOLS,  ETC.  89 

scrapers,  etc.,  ought  to  be  kept  sharp,  and  a  good  Arkansas  stone,  0 
inches  long  and  2  niches  wide,  should  be  provided  to  keep  them  in  con- 
dition. This  should  b.e  used  with  oil,  and  the  blade  of  the  tool  not  con- 
stantly sharpened  in  the  same  direction  in  order  to  avoid  wearing  gnjoves 
in  the  stone.  It  must  be  kept  clean  of  the  black  mixture  of  finely  divided 
steel  and  oil  to  ensure  its  best  sharpening  qualities.  The  workman  must 
know  how  to  put  an  edge  on  his  tools. 

The  following  are  the  principle  bench  tools  in  use  for  metal  work: 

Plate  shears,  straight  and  curved. 

Pliers  (flat-nose),  in  at  least  three  sizes — one  pair  large  and  strong 
enough  to  be  used  in  drawing  wire. 

Pliers  (round-nose),  two  sizes. 

Pliers,  one  pair  with  one  beak  rounded  and  the  other  flat — very 
useful  in  fitting  clasps. 

Side-cutting  nippers  for  removing  that  portion  of  the  platinum  pins 
which  projects  beyond  the  backing. 

Punching  forceps,  for  punching  holes  in  gold  backings,  for  the  platinum 
pins. 

Clasp-bending  forceps. 

Plate  nippers  are  employed  for  removing  redundant  portions  of  a 
plate,  which  they  do  more  rapidly  than  could  be  accomplished  with  files. 

Plate  burnishers,  straight  and  curved. 

Horn  mallet. 

Riveting  hammer. 

Draw  plate  for  reducing  the  size  of  wire. 

Screw  plate  and  taps,  useful  in  the  construction  of  regulating  fixtures. 

Plate  gauge,  standard  American. 

Solder  tweezers  and  tongs. 

Jewellers'  saw  frame  and  saw^s. 

Small  steel  cold  chisels  for  cutting  out  chamber. 

Small  hammer,  weighing  about  2  ounces. 

Round-edged  brass  chaser  for  use  in  forming  vacuum  chambers  and 
for  carrying  the  plate  into  deep  places. 

Hand  vise  and  pin  vise. 

A  small  variety  of  sizes  of  gravers,  chisel  and  gouge  forms.  Those 
made  for  wood  engravers  are  well  tempered  and  answer  admirably  for 
dental  laboratory  uses.  The  graver  will  reach  places  during  the  finish- 
ing of  dentures  which  would  be  inaccessible  to  the  corundum^  wheel. 
They  are  also  useful  in  correcting  slight  imperfections  in  zinc  dies. 

Files,  half  round,  5  or  6  inches  long,  moderately  fine  cut;  round 
files,  small  variety,  ranging  from  6  to  12  inches  in  length,  coarse  and 
fine;  flat  files  with  safe  edge,  moderately  coarse  and  fine.  Files  should 
be  kept  in  a  suitable  rack," and  not  in  a  drawer  with  pliers,  shears,  etc., 
as  contact  with  these  and  with  each  other  will  be  sure  to  damage  them. 

Triangular  steel  scraper  for  removing  file-marks  on  edges  of  plate 
and  backings. 

Small  anvil  set  in  lead. 

Scissors,  straight  and  curved,  for  cutting  patterns  for  plates,  etc. 

Several  points,  made  from  broken  excavators  or  worn-out  pluggers, 


90  THE  lahoratoiiy. 

used  for  marking  upon  gold  or  silver  plates,  picking  wax  or  cement  from 
invested  cases,  and  numerous  other  ])urposes. 

Blue  ])encil  for  marking  plan  of  plate  and  clasj)s  u]K)n  plaster  casts. 

The  additional  tools,  ap])liances,  and  materials  used  in  crown  and 
bridge-work  will  be  described  in  Chapter  XVI 1 1. 

For  vulcanite  work  the  following  are  needed  and  will  be  discussed 
more  in  detail  in  the  chapter  on  that  subject: 

Vulcan  izer. 

Vulcanite  flasks  and  wrenches. 

Flask  press. 

Vulcanite  scrapers. 

Files,  half  round  and  "rat  tail." 

Chisels. 

Calipers  for  measuring  thickness  of  plate. 

Articulators. 

Gas  fitter's  pliers  for  occasional  use  in  tightening  the  bolts  of  vulcanite 
flasks  and  other  rough  work  which  would  damage  the  ordinary  bench 
pliers  are  convenient  articles  to  have,  and  a  small  wood  saw  for  reducing 
size  of  hard  plaster  casts  is  likewise  useful. 

The  use  of  bench  tools  should  be  strictly  confined  to  the  purpose  for 
which  they  were  designed.  They  should  be  carefully  kept  from  contact 
with  plaster  of  Paris,  the  fumes  of  acids,  and  particularly  from  chlorine 
a.s  evolved  from  nitro-hydrochloric  acid  in  the  quartation  process  of 
refining  gold,  which  readily  acts  upon  the  surface  of  steel  and  iron. 


CHAPTER    ri. 

METALS  AND  ALLOYS  USED  IN  PROSTHETIC  DENTISTRY. 
By  Joseph  Dupuy  Hodgejsi,  D.D.S. 

Seventy-eight  elements  are  at  present  known  to  us,  of  wliicli  tiie 
following  is  a  complete  list,  arranged  alphabetically,  with  their  symbols 
and  their  atomic  weights: 


Table  of  Elements  with  International  Atomic  Weights,  1903. 


0  =16.* 

H  =  l.* 

0  =  16.* 

H  =  l.* 

Aluminum 

.     Al 

27.1 

26.9 

Neodymium 

.     Nd 

143.6 

142.5 

Antimony 

.     Sb 

120.2 

119.3 

Neon 

.     Ne 

20.0 

19.9 

Argon 

.     A 

39.9 

39.6 

Nickel 

.     Ni 

58.7 

58.3 

Arsenicum 

.     As 

75.0 

74.4 

Nitrogen    . 

.     N 

14.04 

13.93 

Barium 

.     Ba 

137.4 

136.4 

O.^mium    . 

Os 

191.0 

189.6 

Bismuth    . 

.     Bi 

208.5 

206.9 

Oxygen    . 

0 

16.0 

15.88 

Boron 

.     B 

11.0 

10.9 

Palladium 

Pd 

106.5 

105.7 

Bromine    . 

.     Br 

79.96 

79.36 

Pliosphorus 

P 

31.0 

30.77 

Cadmium  . 

.     Cd 

112.4 

111.6 

Platinum  . 

Pt 

194.8 

193.3 

Caesium    . 

.     Cs 

133.0 

132.0 

Potassium 

K 

39.15 

38.86 

Calcium     . 

.     Ca 

40.1 

39.8 

Praseodymium 

Pr 

140.5 

139.4 

Carbon 

.     C 

12.0 

11.91 

Radium     . 

Rd 

225.0 

223.3 

Cerium 

.     Ce 

140.0 

139.0 

Rhodium  . 

Rh 

103.0 

102.2 

Chlorine     . 

.     CI 

35.45 

35.18 

Rubidium 

Rb 

85.4 

84.8 

Chromium 

.     Cr 

52.1 

51.7 

Ruthenium 

Ru 

101.7 

100.9 

Cobalt 

.     Co 

59.0 

58.56 

Samarium 

Sm 

150.0 

148.9 

Columbium 

.     Cb 

94.0 

93.3 

Scandium 

Sc 

44.1 

43.8 

Copper 

.     Cu 

63.6 

63.1 

Selenium  . 

Se 

79.2 

78.6 

Erbium 

.     Er 

166.0 

164.8 

Silicon 

Si 

28.4 

28.2 

Fluorine     . 

.     F 

19.0 

18.9 

Silver 

Ag 

107.93 

107.12 

Gadolinium 

.     Gd 

156.0 

155.0 

Sodium 

Na 

23.05 

22.88 

Gallium 

.     Ga 

70.0 

69.5 

Strontium 

Sr 

87.6 

86.94 

Germanium 

.     Ge 

72.5 

71.9 

Sulphur     . 

S 

32.06 

31.83 

Glucinum  . 

.     Gl 

9.1 

9.03 

Tantalum 

Ta 

183.0 

181.6 

Gold 

.     Au 

197.2 

195.7 

Tellurium 

Te 

127.6 

126.6 

Helium 

.     He 

4.0 

4.0 

Terbium   . 

Tb 

160.0 

158.8 

Hydrogen 

.     H 

1.008 

1.0 

Thallium  . 

Tl 

204.1 

202.6 

Indium 

.     In 

114.0 

113.1 

Thorium   . 

Th 

232.5 

230.8 

Iodine 

.     I 

126.85 

125.90 

Thulium    . 

Tm 

171.0 

169.7 

Iridium 

.     Ir 

193.0 

191.5 

Tin  . 

Sn 

119.0 

118.1 

Iron 

.     Fe 

55.9 

55.5 

Titanium  . 

Ti 

48.1 

47.7 

Krypton     . 

.     Kr 

81.8 

81.2 

Tungsten  . 

W 

184.0 

182.6 

Lanthanum 

La 

138.9 

137.9 

Uranium   . 

U 

2.38.5 

236.7 

Lead 

.     Pb 

206.9 

205.35 

Vanadium 

V 

51.2 

50.8 

Lithium 

.     Li 

7.03 

6.98 

Xenon 

Xe 

128.0 

127.0 

Magnesium 

.     Mg 

24.36 

24.18 

Ytterbium 

Yb 

173.0 

171.7 

Manganese 

.     Mn 

55.0 

54.6 

Yttrium    . 

Yt 

89.0 

88.3 

Mercury     . 

•     Hg 

200.0 

198.5 

Zinc 

Zn 

65.4 

64.9 

Molybdenum 

.     Mo 

96.0 

95.3 

Zirconium 

Zr 

90.6 

89.9 

VIZ 


These  seventy-eight  elements  are  classed  under  two  great  divisions, 
metallic  and  non-metallic. 


*  It  will  be  understood  that  these  atomic  weights  are  relative;  thus  we  have  a  list,  in  the  first 
column  of  which  oxygen  is  assigned  the  value  of  16.— i.e..  without  fraction  for  greater  convenience 
in  calculation.  In  this  column  hvdrogen  has  a  relative  value  of  l.OOS.  /l  he  second  column  is  a 
list  of  the  atomic  weights  with  hydrogen  taken  as  the  standard,  when  relatively  o.xygen  becomes 
equal  to  15.88 

91 


Barium, 

Cobalt, 

Manganesium, 

Cadmium, 

Arsenicum, 

Titanium, 

Chromium, 

ITranium. 

92      METALS  AM)  ALLOYS   r.S'AV)    /.V   PROSTIIKTW  DKNTLSTRY. 

THE  METALS. 

Of  tlu'  sixty-two  (•l('iiu'iit;irv.sul)staiic(>.s  known  jis  metals  onl y  t'ourtfcn 
arc  ordiiiarily  i'nij)k)y('(l  in  tlu-ir  tnic  nictallic  condition.     I'lu'.sc  arc: 

Iron,  .Muniiiiuni,  Gold, 

Copper,  Nickel,  Silver. 

Lead,  Antimony,  Mercury, 

Zinc,  Magnesium,  Platinum. 

Tin,  Bismuth, 

About  twelve  are  more  or  les.s  useful  in  the  preparation  of  medicines, 
in  the  arts  for  coloring  pigments,  and  for  alloying  purposes.    These  are: 

Potassium, 
Sodium, 
Calcium, 
Lithium, 

The  remaining  thirty-six  are  more  or  less  rare,  and  as  yet  of  little 
or  no  practical  value  in  the  metallic  state. 

The  metallurgist  groups  the  metals  into  two  classes,  which  are  knowD 
as  noble  and  base: 

Noble  Metals. — Noble  metals  are  those  whose  compounds  with  oxygen 
are  decomposable  by  heat  alone,  at  a  temperature  not  exceeding  redness. 
These  are: 

Mercury,  Platinum,  Ruthenium, 

Silver,  Palladium,  Osmium, 

Gold,  Rhodium,  Iridium. 

Base  Metals. — Base  metals  are  those  whose  compounds  with  oxygen  are 
not  decomposable  by  heat  alone,  retaining  oxygen  at  high  temperatures. 

The  base  metals  are  further  subdivided  with  reference  to  their  affinity 
for  oxygen  and  other  chemical  properties. 

First  division.  This  contains  five  metals.  They  are  very  readily 
oxidized,  and  their  oxides  are  all  soluble  in  water,  giving  it  a  strongly 
alkaline  reaction;  so  also  are  their  phosphates  and  carbonates,  with  the 
exception  of  lithium  phosphate,  which  is  quite  insoluble,  and  the  carbon- 
ate, which  is  only  sparingly  soluble.  They  all  energetically  decompose 
water  at  ordinary  temperatures,  liberating  hydrogen  and  forming 
hydrates  in  solution.  They  are  soft,  of  low  specific  gravity,  and  fusible 
at  low  temperatures.     These  are: 

Potassium,  Lithium,  Caesium 

Sodium,  Rubidium, 

Second  division.  This  contains  four  metals,  all  of  which,  with  the 
exception  of  magnesium,  decompose  water  at  ordinary  temperatures, 
combining  with  the  oxygen.  Their  oxides  are  more  or  less  soluble  in 
water,  rendering  it  alkaline ;  but  their  neutral  carbonates  and  phosphates 
are  insoluble.    These  are: 

Barium,  Strontium,  Calcium, 

Magnesium. 


PROrKRTIP:S  OF  Tlir.   METALS.  93 

Third  division.  This  contains  tliirtccn  metals,  of  wliich  but  three 
are  of  much  importance.  Those  which  have  been  isolated  do  not 
decompose  water  at  ordinary  temperatures  without  the  addition  of  a 
weak  acid  or  a  slight  rise  of  temperature.  Their  oxides  and  carbonates 
are  insoluble  in  water.    These  are: 

Aluminum,  Thorium,  Cerium, 

Chromium,  Yttrium,  Lanthanum, 

Titanium,  Zirconium,  Didymium, 

Glucinum,  Erbium,  Tantalum, 

Columbium 

Fourth  division.  This  contains  nine  metals,  the  chief  of  which 
decompose  water  at  a  red  heat.    These  are: 

Iron,  Manganesium,  Vanadium, 

Nickel,  Zinc,  Thallium, 

Cobalt.  Uranium,  Indium. 

Fiph  division.  This  contains  four  metals,  which  do  not  decompose 
water  at  any  temperature.    These  are: 

Cadmium,  Leao,  Bismuth, 

Coppei . 

Sixth  division.  This  contains  six  metals.  All  the  higher  oxides  of 
these  metals  have  acid  properties.     These  are: 

Tin,  Arsenicum,  Tungsten, 

Antimony,  Molybdenum,  Tellurium. 

PROPERTIES  OF  THE  METALS. 

A  metal  is  an  elementary  substance,  solid  at  ordinary  temperatures, 
with  the  single  exception  of  mercury  (a  liquid  solidifying  at  — 39°  C), 
having  a  peculiar  lustre,  called  "metallic  lustre,"  and  the  property  of 
replacing  hydrogen  in  chemical  reactions,  as,  for  example, 

Zn  +  H2SO4  =  ZnSO,  +  Hj, 

insoluble  in  water,  a  good  conductor  of  heat  and  electricity,  and  possess- 
ing the  quality  of  uniting  with  oxygen  to  form  a  basic  oxide. 

No  line  can  be  sharply  drawn  between  metals  and  non-metals;  just 
as  none  can  be  drawn  between  soluble  and  insoluble,  poisonous  and 
non-poisonous  substances,  yet,  from  a  general  point  of  view,  this  class 
of  elements  admits  of  the  foregoing  definition. 

The  metals  possess  a  number  of  characteristic  properties,  which  may 
be  noted  as  follows: 

Non-transparency. — Metals,  as  a  rule,  are  non-transparent,  or  opaque, 
yet  some  have  proven  to  possess  the  property  of  transparency  in  a  low 
degree  at  least.  In  the  case  of  gold,  through  the  leaf,  or  thin  films 
produced  chemically  on  glass  plate,  a  light-green  color  is  transmitted. 
Also  very  thin  films  of  mercury  are  said  to  transmit  light  with  a  violet- 


94      METALS  AM)  ALLOYS   USED   L\   I'ROSTlIi: IIC  DKyTISTRY. 

blue  color,  and  copper,  it  is  claimed,  is  somewhat  translucent;  while 
silver  in  infinitely  thin  films  is  absolutely  opaque. 

Color. — The  color  of  most  metals  is  white,  and  ranges  from  the  pure 
white  of  silver  and  tin  to  the  bluish  hue  of  lead.  Bismuth  is  a  light 
gray,  with  a  delicate  tinge  of  red.  Copper  is  called  tlie  "red  metal." 
Gold  is  a  rich  yellow,  barium  and  strontium  a  straw  color,  while  calcium 
exhibits  a  little  deeper  shade  of  that  color. 

Luster. — Polished  metallic  surfaces,  like  those  of  other  solids,  divide 
any  incident  ray  into  two  parts,  of  which  one  Ls  refracted,  while  the 
other  is  reflected,  with  this  difference,  however,  that  the  former  is 
completely  absorbed,  while  the  latter  is  reflected,  which  latter  accounts 
in  all  likelihood  for  the  metallic  luster. 

Odor  and  Taste. — ^Nlost  metals  are  destitute  of  odor  and  taste.  Peculiar 
odors  are,  however,  evolved  from  some  of  them  when  Ideated;  in  fact, 
one  of  the  means  of  discriminating  arsenicum  consists  in  the  recognition 
of  its  characteristic  smell  of  garlic  when  heated.  Ircn,  copper  or  zinc 
when  heated  also  evolve  peculiar  odors.  The  taste  whi.h  is  perceived 
in  some  is  no  doubt  due  to  their  peculiar  character,  although  in  some 
cases  it  may  depend  upon  voltaic  action  set  up  by  the  chemical  agency 
of  the  saliva,  the  metal  not  being  perfectly  pure.  If  a  piece  of  zinc  be 
placed  upon  the  tongue,  and  a  piece  of  silver  luider  it,  and  the  edges 
joined,  a  metallic  taste  will  be  perceived  dependent  on  slow  solution  of 
the  zinc  under  electric  action.  The  odor.  Dr.  Essig  says,*  "ni^y  be 
noticed  in  a  marked  degree  when  holding  in  the  hand  a  mass  of  an 
alloy  composed  of  gold,  platinum,  tin,  and  silver  prepared  for  use  as 
amalgam.  The  moisture  of  the  hand,  aided  by  its  heightened  temper- 
ature, seems  to  promote  the  electric  action." 

Crystalline  Form. — Most  metals  are  capable  of  crystallization,  and 
their  crystals  belong  to  the  following  systems:  Regular — silver,  gold, 
palladium,  mercury,  copper,  iron,  lead;  quadratic — tin,  potassium; 
rhombic — antimony,  bismuth,  tellurium,  zinc,  magnesium. 

Perhaps  all  metals  in  soldifying  assume  a  crystalline  structure,  which 
differs  only  in  degree  of  visibility.  Antimony,  bismuth,  and  zinc  exliibit 
a  very  distinct  crystalline  structure  plainly  visible  in  broken  ingots.  Tin 
is  also  crystalline,  which  fact  is  evinced  by  the  "tin  cry"  when  a  bar 
of  the  metal  is  bent,  the  crystal  faces  sliding  over  one  another;  but  the 
bar  is  not  easily  broken,  and  exhibits  an  apparently  non-crystalline 
fracture.  Gold,  silver,  copper,  aluminum,  cadmium,  iron,  lead,  cobalt, 
and  nickel  are  practically  amorphous,  the  crystals  being  so  closely 
packed  as  to  virtually  produce  a  homogeneous  mass. 

Malleability,  Ductility,  and  Tenacity. — ^These  are  properties  possessed 
by  some  metals  by  reast)n  of  the  cohesive  power  of  their  molecules, 
and  are  to  that  extent  kinrlred. 

IVIalleability. — Malleability  is  that  quality  possessed  by  a  metal 
which  permits  it  to  be  hammered  or  rolled  into  thin  sheets  without  breach 
of  continuity.  While  many  metals  possess  this  property  to  some 
degree,  it  is  most   wonderfully  exemplified    in   gold.     Leaves    of   this 

1  Dental  Metallurgy,  p.  20. 


PROrEIlTIKS   OF   Till-:   Mrri'ALS. 


9") 


metal  have  been  produced  1^7-770  0^5-  of  an  ineh  in  tliickncss,  each  grain 
of  which  will  cover  an  area  of  75  square  inches. 

Ductility. — Ductility  is  that  property  possessed  by  some  metals  by 
virtue  of  which  they  may  be  drawn  into  wire.  The  operation  consists 
in  forcibly  drawing  the  metal  through  a  series  of  holes,  in  a  hard-steel 
draw-plate,  which  gradually  decrease  in  size.  Gold  is  also  the  most 
ductile  of  all  metals,  a  single  grain  of  it  having  been  drawn  into  a  wire 
550  feet  in  length.  This  was  accomplished  by  covering  the  gold  wire 
with  silver,  which  is  also  remarkably  ductile,  thus  making  a  composite 
wire  of  greater  thickness.  After  drawing  this  down  to  the  greatest 
possible  degree  of  tenuity,  the  silver  was  dissolved  off  by  nitric  acid, 
leaving  a  gold  wire  -g-oVo"  ^^  ^^^  ^'^^^  "^  diameter. 

Tenacity. — Tenacity  is  tliat  property  possessed  by  metals,  in  conse- 
quence of  which  they  resist  rupture  when  exposed  to  tension.  Their 
relative  tenacity  may  be  ascertained  by  preparing  wires  of  exactly  equal 
diamet  rs  and  comparing  the  number  of  pounds  weight  each  will  sustain 
before  rupture. 

These  properties  are  shown  relatively  for  some  of  the  more  important 
metals  in  the  following  table: 


Malleability. 

Ductility. 

Tenacity. 

1.  Gold. 

1.  Gold. 

1.   Iron. 

2.  Silver. 

2.  Silver. 

2.  Copper. 

3.  Copper. 

3.  Platinum. 

3.  Platinum, 

4.  Tin. 

4.  Iron. 

4.  Silver. 

5.  Cadmium. 

5.  Nickel. 

5.  Gold. 

6.   Platinum. 

6.  Copper. 

6.  Zinc. 

7.  Lead. 

7.  Palladium. 

7.  Tin. 

8.  Zinc. 

8.  Aluminum. 

8.  Lead. 

9.  Iron. 

9.  Cadmium. 

10.  Nickel. 

10.  Zinc. 

11.  Palladium. 

11.  Tin. 

12.  Lead. 

The  two  properties  of  malleability  and  ductility  are  closely  related 
to  each  other,  yet,  as  may  be  seen  from  the  above  table,  they  do  not 
always  parallel  each  other,  for  the  reason  that  ductility  in  a  higher  degree 
than  malleability  is  determined  by  the  tenacity  of  the  metal;  for  example, 
tin,  though  quite  malleable,  is  very  slightly  ductile,  and  iron,  while 
ninth  in  point  of  malleability,  is  fourth  in  ductility.  In  the  operation 
of  hammering  out  a  metal  which  the  quality  of  malleability  permits 
the  granular  particles  are  flattened  and  spread  in  all  directions,  while 
in  those  allowed  by  its  ductility  each  granular  particle  is  elongated 
into  a  fibre. 

There  are  several  conditions  which  materially  modify  the  properties  of 
malleability,  ductility,  and  tenacity,  one  of  the  most  important  of  which 
is  the  state  of  purity  of  the  metal.  Gold  is  the  most  malleable  of  all 
metals,  yet  if  the  merest  trace  of  lead,  itself  a  soft  and  malleable  metal, 
be  contained  in  it,  the  gold  becomes  too  brittle  to  be  worked,  and 
especially  is  this  the  case  if  the  gold  contains  any  silver,  as  is  frequently 
the  case.    This  destruction   of  malleability  and  tenacity  is  yet  more 


96      METALS  AM)   ALLOYS    USED   L\  rROSTLIETIC  DENTISTRY. 

proiiouiKcd  when  aiitiiiiony  or  similar  metals  are  mixed  with  fjold,  even 
in  minnte  (iiiantities.^ 

Temperature  also  exereises  a  very  great  modifying  influenee  over  these 
properties;  for  example,  a  bar  of  zinc  obtained  by  easting  is  exceedingly 
brittle,  but  when  heated  to  100°  or  150°  C.  it  may  be  rolled  into  thin 
sheets  or  drawn  into  wire.  Such  sheet  or  wire  then  remains  malleable 
and  ductile  after  cooling.  The  explanation  of  this  remarkable  fact  is, 
that  the  loosely  cohering  crystals  have  become  intertwisted  and  forced 
into  absolute  contact  with  each  other,  and  this  is  supported  hy  the  fact 
tliat  the  rolled  zinc  has  a  somewhat  higher  specific  gravity  than  the 
original  ingot.  If  the  temperature  be  carried  to  205°  C.  the  metal  again 
becomes  so  brittle  that  it  may  be  powdered  in  a  mortar.  Extreme  care, 
therefore,  must  be  exercised  in  the  handling  of  hot  zinc  dies,  for  if  by 
accident  one  be  dropped  upon  a  hard  surface  it  is  likely  to  be  spoiled. 
Aluminum,  magnesium,  and  some  other  metals,  which  at  ordinary 
temperatures  possess  little  or  no  ductility,  may  be  drawn  into  wire  when 
heated. 

These  qualities  are  greatly  diminished  in  alloys  by  heating.  Some 
forms  of  brass,  for  example,  which  are  soft,  tenacious,  and  ductile  at 
ordinary  temperatures,  are  made  quite  brittle  by  heating  to  dull  redness. 
Again,  it  is  quite  certain  that  18-carat  gold  solder  is  brittle  at  red  heat. 

The  tenacity  of  metals  in  general  is  greatly  diminished  })y  heating. 
The  exceptions  to  this  are  in  the  cases  of  iron,  steel,  and  gold. 

The  following  table  shows  the  results  obtained  by  Wertheim'  in  his 
experiments  on  a  number  of  the  metals  at  temperatures  from  15°  to 
20°  C: 


Permanent  vdre  one  square  mm.  sec- 
tion, weight  in  (in  kilos)  causing 


Name. 

Iron,  drawn  . 
'      annealed 
Copper,  drawn 

"       annealed   . 
Platinum,  drawn    . 
"  annealed 

Silver,  drawn 

"        annealed 
Gold,  drawn 

"     annealed 
Zinc,  drawn 

"      annealed 
Tin,  drawn    . 
"     annealed 
Lead,  drawn 
"      annealed 


Permanent  elon- 

gation of 

Breakage 

1201100 

32.0 

61.0 

Under    5.0 

47.0 

12.0 

40.0 

Under    S.O 

30.0 

34.0 

23.0 

11.3 

29.0 

2.6 

16.0 

13.5 

27.0 

3.0 

10.0 

0.75 

13.0 

1.0 

0.45 

2.45 

0.2 

0.25 

2.1 

02 

1.8 

Annealing. — Pure  iron,  copper,  silver,  and  other  metals  are  easily 
drawn  into  wire,  rolled  into  sheets,  or  flattened  under  the  hammer.    But 


1  See  Gold. 

2  Annales  de  Chimie  et  de  Phy.'^ique  (III.),  vol.  xii. 


PROPERTIES   OF  THE  METALS.  97 

all  these  operations  iviulor  the  metals  harder,  and  reduce  from  their 
pliability.  Their  original  softness  can  be  restored  to  them  by  annealing 
— L  e.,  by  heating  them  more  or  less  and  then  plunging  them  into  cool 
water,  oil,  etc.  In  the  case  of  iron,  however,  this  applies  only  if  the 
metal  is  perfectly  pure.  If  it  contains  a  few  parts  carbon  per  thousand, 
the  annealing  process,  instead  of  softening  the  metal,  gives  it  a  "temper," 
meaning  a  higher  degree  of  hardness  and  elasticity.^ 

Welding. — The  process  of  joining  two  clean  surfaces  of  a  metal 
together  by  pressure  is  called  v^elding.  This  property  is  possessed  by 
iron  at  white  heat,  but  lead  and  gold  will  cohere  at  ordinary  temperatures 
in  proportion  to  their  purity.  Two  pieces  of  iron  may  be  welded  by 
a  current  of  electricity  sent  through  their  junction,  when  the  metal  is 
heated  by  the  resistance  offered  to  the  passage  of  the  current. 

Forging. — The  process  of  hammering  metals  out  into  various  shapes 
is  called  forging.  With  some  it  may  be  done  when  they  are  cold, 
while  in  others  tljpy  must  be  hot.     It  illustrates  the  solid  flow  of  metals. 

Elasticity, — All  metals  are  elastic  to  this  extent,  that  a  change  in  their 
form  brought  about  by  a  stress  not  exceeding  certain  limit  values,  will 
disappear  when  the  stress  is  removed.  Strains  exceeding  the  "limit  of 
elasticity"  result  in  permanent  deformation,  or,  if  sufficiently  great,  in 
rupture.  This  property  may  be  increased  in  some  metals  by  compound- 
ing and  alloying.  Thus,  iron  compounded  with  the  proper  amount  of 
carbon,  has  its  elasticity  increased  to  the  very  highest  degree,  while  the 
metal  itself  is  almost  devoid  of  the  quality.  The  same  is  true  of  copper 
and  zinc  in  some  forms  of  brass,  also  of  gold  and  platinum  when 
alloyed  with  copper ;  both  the  latter  are  soft  and  have  little  elasticity,  yet 
when  combined  in  proper  proportions  with  copper  an  alloy  is  produced 
which  is  quite  elastic,  and  may  be  used  for  clasps  for  artificial  dentures. 

Sonorousness. — ^This  is  a  property  possessed  by  the  harder  metals, 
and  is  quite  marked  in  certain  alloys,  such  as  those  of  copper  and  tin 
known  as  bell-metal.  Lead,  which  is  but  feebly,  if  at  all,  sonorous,  may 
become  so,  it  is  claimed,  if  cast  in  the  shape  of  a  mushroom.  Aluminum 
emits  a  characteristic  sound  when  struck.  The  first  article  known  to 
have  been  made  of  aluminum  was  a  baby  rattle  for  the  infant  prince 
imperial  of  France,  for  which  purpose  it  was  well  fitted  on  account  of 
its  sonorousness.  Impurities  sometimes  increase  the  sonorousness  of  a 
metal,  as  in  the  case  of  antimony  in  lead. 

Fusibility  and  Volatility. — All  metals  may  be  fused,  and  most  of  them 
are  capable  of  being  volatilized,  but  the  temperature  at  which  they 
become  fluid  differs  greatly  in  different  metals,  as  the  following  table 
shows : 


Fusing  point. 

Fusing  point. 

Name  of  metal. 

Centigrade. 

Fahrenheit. 

Authority. 

Mercury 

—39.0 

—38.2 

Csesium 

+  26  to  27.0 

+78.8 

Setterberg. 

Gallium 

30.0 

S6.0 

L.  de  Boisbau 

Rubidium  . 

38.5 

101.3 

Bunsen. 

Potassium 

■      .                        62.5 
1  See  Iron. 

144.5 

Bunsen. 

98      METALS  AND  ALLOYS   USED  IN  PROSTHETIC  DENTISTRY. 


Names  of  metal. 
Sodium 
Indium 
Lithium 
Tin    . 
Bismuth     . 
Thaliuni     . 
Cadmium  . 
Lead 
Zinc  . 

Antimony  . 
Incipient  red  heat 
Aluminum 
Magnesium 
Cherry-red  heat    . 
Silver 
Gold 

Yellow  heat 
Copper 
Iron,  wrought 
Iron,  chemically  pure 
Cobalt 
Nickel 
Uranium    . 
Dazzling  white  heat 
Palladium 
Oxyhydrogen  flame 
Platinum    . 
Iridium 
Rhodium    . 
Ruthenium 
Maximum      temperature     of 


Fusing  point. 

Fusing  point. 

Centigrade. 

Fabreulieit. 

Autliority. 

95.5 

203.9 

Bunsen. 

176.0 

348.8 

Richter  (?). 

180.0 

356.0 

(?) 

228.0 

442.4 

Rudberg. 

264.0 

507.2 

Rudberg. 

290.0 

554.0 

Lamy. 

320.0 

608.0 

Rudberg. 

325.0 

617.0 

415.0 

779.0 

Person. 

425.0 

797.0 

525.0 

977.0 

Pouillet. 

625.0 

1157.0 

750.0 

1382.0 

700.0 

1292.0 

Pouillet. 

1040.0 

1904.0 

Becquerel.  ^ 

1100.0 

201 2.0*. 

1100  0 

2012.0 

Pouillet. 

1200.0 

2192.0 

1300  to  1400.0 

2372  to  2552.0 

higher-1600  0 

2912  0 

1400.0 

2552  0 

1600  0 

2912.0 

(?) 

(?) 

1.500  to  KiOO.O 

2732  to  2912.0 

Pouillet. 

1600.0 

2912.0 

2000.0 


3632.0 


2S70.0  5198.0 

2870° — i.e.,  is  as  yet  infusible. 


Bunsen. 


oxyhydrogen  flame     . 
Osmivim  does  not  melt  at 

Metals  may  be  characterized  as  fixed  and  volatile.  Of  their  volatility 
we  have  little  precise  knowledge.  The  boiling  points  of  a  few  are  given 
in  the  following  table: 

Authority. 
Regnault. 
Deville  and  Troost 
Deville  and  Troost 
Dewar  and  Dittmar. 

metals  may  be  clas.sed  as 


Name  of  metal. 
Mercury 
Cadmium 
Zinc 

Potassium 
Sodium 


Boiling  point. 

357.3°  C. 

860.0°  " 

1040.0°  " 

Below  1040.0°  " 

Above  1040.0°  " 


For  practical  purposes  the  volatility  of 
follows : 

1.  Distillable  below  redress:     Mercury. 

2.  Those  distillable  at  red  heats. 


Cadmium, 
Zinc, 


Magnesium, 
Potassium, 


Sodium. 


>  Jahresb.  f.  Chem.,  1867,  p.  41  ;  Phil.  Mag.,  xxxiv.  489. 


PROPERTIES  OF  THE  METALS. 


90 


3.  Those   which   are  vohitiHzed   more   or   less    readily  when  heated 
beyond  their  fusing  points  in  open  crucibles  : 


Antiuujiiy  (very  readily),        Bismuth, 
Ijead,    ,  Tin, 


Silver. 


4.  Those  which  are  with  very  great  difficulty  volatilized,  if  at  all  : 

Gold,  Copper  (?). 

5.  Those*  which  are  practically  "fixed,"  or  non-volatile  : 


Copper  (?), 

Cobalt, 

Lithium, 

Iron, 

Calcium, 

Strontium, 

Nickel, 

Aluminum, 

Barium. 

"In  the  oxyhydrogen  flame  silver  boils,  forming  a  blue  vapor,  while 
platinum  volatilizes  slowly,  and  osmium,  though  infusible,  very  readily."^ 

"It  is  doubtful,"  says  Makins,  "if  it  (gold)  is  volatile  per  se.  But  if 
gold  be  alloyed  with  copper,  it  has  been  shown  by  Napier  to  be  con- 
siderably volatilized,  so  that  quantities,  amounting  to  4^  grains,  could 
be  collected  during  the  pouring  out  of  30  pounds'  weight  from  a 
crucible.  .  .  .  That  mixtures  of  gold,  silver,  and  lead,  when 
cupelled  together,  volatilize  considerably." 

Specific  Heat. — Equal  weights  of  different  metals  have  been  found  to 
absorb  different  amounts  of  heat  when  subjected  to  the  same  temper- 
ature. They,  indeed,  possess  different  capacities  for  heat.  Thus,  the 
amount  of  heat  necessary  to  raise  a  given  weight  of  water  has  been  found 
to  be  31  times  as  great  as  that  required  to  raise  an  equal  weight  of 
platinum  through  the  same  range  of  temperature;  or,  in  other  words, 
the  amount  of  heat  required  to  raise  a  given  weight  of  water  through 
100°  C.  will  raise  31  times  the  same  weight  of  platinum  through  100°  C. 
of  temperature.  Thus,  water  being  taken  as  the  standard  or  unit,  the 
specific  heat  of  platinum  is  ^\-,  or  0.032  that  of  water. 


Table  op  Specific  Heats 


1.  Iron 

2.  Nickel     . 

3.  Cobalt    . 

4.  Zinc 

5.  Copper  . 

6.  Palladium 

7.  Silver  . 
S.  Cadmium 
9.  Tin 

10.  Antimony 

11.  Mercury 

12.  Gold       . 

13.  Platinum 

14.  Lead 

15.  Bismuth 


0.1138 
0.1086 
0.1070 
0.0956 
0.0952 
0.0593 
0.0570 
0.0567 
0.0562 
0.0508 
0.0333 
0.0324 
0.0322 
0.0314 
0.0308 


1  William  Dittmar. 


100     METALS  AND   ALLOYS   USED   L\  PROSTHETIC  DEyVISTRY. 

Expansibility. — The  expansion  of  metals  by  lieat  varies  greatly.  The 
coefficient  of  expansion  is  constant  only  in  metals  that  crystallize  in  the 
regular  system.  The  others  expand  differently  in  the  direction  of  the 
different  axes  of  their  crystals,  and  to  eliminate  this  source  of  uncer- 
tainty in  making  estimates  of  their  expansibility,  they  are  employed 
as  compressed  powders. 

The  following  table  gives  the  linear  expansion  from  0°  to  100°  C, 
according  to  Fizeau,  the  length  at  0°  being  taken  as  unity.^ 

Kxpansion. 
Name  of  metal.  0°  to  100°  C. 


Platinum,  cast 

Gold,  cast 

Silver,  cast 

Copper,  native 

Copper,  artificial 

Iron,  soft 

Steel,  cast 

Bismuth,  mean  expansion 

Tin,  compressed  powder     . 

Lead,  cast 

Zinc         .... 

Cadmium,  compressed  powder 

Aluminum,  cast 

Mercury 


0.000907 

0.001451. 

0.001936 

0.001708 

0.001869 

0.001228 

0.001110 

0.001374 

0.002269 

0.002948 

0.002905 

0.003102 

0.002336 

0.018153 


"The  high  rate  of  expansibility  of  zinc  renders  it  particularly  vaUiable 
as  a  metal  for  dies  upon  which  to  form  plates  for  the  mouth  in  many 
cases.  The  metal  is  ca.st  while  fluid  and  at  its  extreme  limit  of  ex|)ansion, 
which  upon  cooling  returns  to  its  minimum  dimensions,  and  thus 
furnishes  a  cast  a  little  smaller  than  the  plaster  model  which  it  represents. 
It  has  been  found  that  this  contraction  of  the  zinc  die  a  trifle  more  than 
compensates  for  the  expansion  which  takes  place  in  the  plaster  model 
in  setting,  and  in  the  majority  of  cases  a  plate  made  thereon  adapts 
itself  more  accurately  to  the  mouth  than  one  made  upon  a  die  of  less 
expansible  metal.  Even  if  the  contraction  undergone  by  the  zinc  is  so 
great  as  to  produce  a  die  somewhat  smaller  than  the  mouth,  so  far  from 
being  a  detriment,  it  is  a  positive  advantage  in  most  cases  of  full  upper 
replacement,  as  under  such  conditions  the  pressure  of  the  finished  plate 
i.s  greater  upon  the  alveolar  riflge  than  upon  the  central  portions  of  the 
hard  palate — a  state  of  affairs  the  advantages  of  which  are  sufficiently 
obvious  without  explanation."^ 

Conductivity. — Metals  are  good  conductors  of  heat  and  electricity,  but 
these  fjualities  are  very  differently  exhibited  in  different  metals.  An 
exact  knowledge  of  these  conductivities  is  of  great  scientific  and  practical 
importance  to  the  dentist,  and  too  much  attention  cannot  be  given  their 
consideration. 

The  following  table  gives  the  thermic  and  electric  conductivities  of 
some  of  the  more  important  metals  and  alloys: 

^  W^illiam  Dittmar. 

a  Dr.  E.  C.  Kirk,  Am.  System  of  Dentistry,  vol.  iii.  p.  793. 


PROPERTIES  OE  THE  METALS. 


101 


Name  of  metal. 

Silver 

Copper 

Gold 

Tin   . 

Iron 

Lead 

Platinum 

Bismuth 

Brass 

Steel 

German  silver 

Rose  fusible  metal 

Pianoforte  Wire 


Relative  conductivity. 


Thermic. 

Electric,  at  0°  C. 

100.0 

100.00 

73.G 

99.95 

.       53.2 

77.90 

14.5 

12.30 

11.9 

16.81 

8.5 

8.32 

8.4 

18.80 

1.8 

1.24 

.       23.6 

.       11.6 

7.3 

7.67 

2.8 

14.40 


Makins  states  that  among  the  results  of  Dr.  Matthiessen's  experiments 
upon  the  electric  conductivity  of  metals  "are  the  facts  that  impurity  of 
a  metal  or  alloying  it  greatly  diminishes  its  conducting  power.  Rise  of 
temperature  again  has  the  same  effect.  Thus  between  32°  F.  and  212° 
(or  0°  C.  and  100°)  great  diminution  takes  place,  and  that  not  uniformly, 
as  some  lose  it  much  more  in  proportion  than  others,  by  thus  raising 
the  temperature.  Many  lose  as  much  as  25  per  cent,  of  their  conducting 
power." 

An  illustration  of  the  comparative  conductivity  of  the  metals  is 
observed  in  the  electric  furnaces  with  platinum  coils.  The  electricity 
is  readily  transmitted  from  its  source  by  the  copper  efferent  wire,  but 
when  it  meets  the  platinum  that  metal  offers  so  much  resistance  to  the 
passage  of  the  current,  on  account  of  its  low  conducting  power,  that  it 
becomes  white-heated — incandescent. 

Specific  Gravity. — ^This  property  varies  in  different  metals  from  0.594 
(lithium)  to  22.48  (osmium),  as  the  following  table  shows: 


Name  of  metal 

Specific  gravity. 

Authority. 

Lithium 

0.594 

Bunsen. 

Potassium 

0.875 

Baumhauer. 

Sodium 

0.9735 

Baumhauer. 

Rubidium 

1.52 

Bunsen. . 

Calcium 

1.578 

Bunsen  and  Matthiessen 

Magnesium 

1.743 

Bunsen. 

Caesium 

1.88 

Setterberg. 

Glucinum    ' 

.        .         2.1 

Debray. 

Strontium 

2.5 

Aluminum 

2.583 

MaUet. 

Barium 

.     Over    4.0 

Clarke. 

Zirconium 

4.15 

Troost. 

Vanadium 

5.5 

Roscoe. 

Gallium 

5.9 

Lecoq  de  Boisbaudran. 

Lanthanum 

6.163 

Lecoq  de  Boisbaudran. 

Didymium 

6.544 

Hillebrandt  and  Norton. 

Antimony- 

6.715 

Marchand  and  Scheerer. 

Cerium 

6.728 

Hillebrandt  and  Norton. 

Chromium 

6.81 

Wohler. 

102     METALS  AM)   ALLOYS    USED    L\  PROSTll ETK'  DKSTISTRY 


Name  of  metal. 
Zinc 

Manganesium 
Till 

Indiiiin 
Iron 
Nickel  . 
Cadmium 
Cobalt  . 
Molybdenum 
Copper 
Bismuth 
Silver   . 
Lead     . 
Palladium 
Thallium 
Rhodium 
Ruthenium 
Mercury 
Tungsten 
Uranium 
Gold     . 
Platinum 
Iridium 
Osmium 


Specific  gravity 

Authority, 

6.915 

Karsten. 

7.14 

Brunner. 

7.29      - 

7.42 

Richter. 

7.S44 

Berzelius. 

8.279 

Richter. 

8.546 

Schroder. 

8.5 

8.6 

Uebray. 

S.94 

9.823 

Holzmann. 

10.4 

HolzmauM. 

11.25 

Deville. 

11.4 

Deville  and  Debray 

11.86 

Crookes. 

12.1 

Bunsen. 

12.26 

Deville  and  Deliray 

13.595 

H.  Kopp. 

16.54 

Wohler. 

18.33 

Peligot. 

19.265 

Matthiessen. 

21.46 

22.4 

22.477 

Deville  and  Debray 

COMPOUNDS  OF  METALS  AND  NON-METALS. 


Metals  mix  with  each  other  indefinitely  to  form  alloys,  preserving  the 
metallic  appearance  and  properties.  •  They  combine  with  non-metals 
in  definite  chemical  proportions  to  form  compomids  of  a  more  precise 
natnre,  in  which  case  the  metallic  characters  are  almost  invariably  lost. 
These  definite  compounds  include  the 


Oxides 

Sulphides, 

Chlorides, 


They  also  combine  with 

Nitrogen, 
Phosphorus, 


Bromides, 
Fluorides, 
Cyanides, 


Boron, 
Silicon, 


Selenides, 
Tellurides 


Caibon. 


ALLOYS. 


An  alloy  is  the  compound  or  mixture  of  two  or  more  metals  elTected 
by  fusion. 

An  amalgam  is  an  alloy  of  two  or  more  metals,  one  of  which  is  mercury. 

Few  metals  are  employed  in  the  pure  state,  with  the  exception  of 
iron,  copper,  lead,  tin,  zinc,  platinum,  and  ahnninum;  they  are  more 
frequently  used  for  technical  purposes  in  the  form  of  alloys.     Every 


ALLOYS. 


103 


industrial  application  requires  special  (jualities  that  may  not  exist  in 
any  single  metal,  but  which  may  be  produced  by  the  proper  mixture 
of  two  or  more.  For  example,  silver  and  gold  are  much  too  soft  and 
pliable  for  plate,  coin,  or  jewelry,  but  by  the  addition  of  certain  amounts 
of  copper  they  are  rendered  harder  and  more  elastic,  while  their  color 
and  other  valuable  qualities  are  not  impaired.  Copper  is  also  too  soft 
and  tough  to  be  wrought  in  a  lathe,  but  when  alloyed  with  zinc  it  forms 
a  hard,  beautiful,  yellow-colored  alloy  known  as  brass,  of  great  usefulness 
and  more  easily  worked  than  the  pure  metal. 

Alloys  are  extremely  interesting,  from  a  scientific  standpoint,  for  they 
may  be  regarded  not  only  as  mere  mixtures  of  metals,  but  in  many 
instances  as  true  chemical  compounds.  Matthiessen^  regarded  it  as 
probable  that  the  condition  of  an  alloy  of  two  metals  in  a  melted  state 
may  be  either  that  of  (1)  a  solution  of  one  metal  in  another;  (2)  a 
chemical  combination  ;  (3)  a  mechanical  mixture  or ;  (4)  a  solution  or 
mixture  of  two  or  all  of  the  above ;  and  that  similar  differences  may 
exist  as  to  its  condition  in  the  solid  state,  defining  a  solid  solution  as 
"a  perfectly  homogeneous  diffusion  of  one  body  in  another." 

The  Physical  Properties  of  Alloys. — ^The  physical  properties  of  an 
alloy  cannot  be  anticipated  from  those  of  its  constituent  metals,  and 
are  only  determinable  by  actual  experiment.  Very  minute  proportions 
of  some  metals  added  to  others  will  produce  an  alloy  with  proper- 
ties foreign  to  either  of  the  constituents.  Thus,  a  small  quantity  of 
lead  fused  with  gold  will  produce  a  brittle  alloy,  though  each  metal 
is  malleable. 

Specific  Gravity. — If  this  property  be  calculated  as  the  mean  of  that 
of  the  component  metals  of  the  alloy,  the  result  may  be  greater  than, 
equal  to,  or  less  than  the  actual  specific  gravity  of  the  alloy  determined 
by  experiment.  Thus,  the  alloys  of  silver  and  gold  have  a  less  specific 
gravity  than  the  theoretical  mean  of  the  components;  whereas  copper 
and  zinc  vary  in  the  opposite  direction. 

The  following  table,^  by  Thenard,  shows  examples  of  this  variation: 


Alloys  possessing  a 

greater  specific 

Alloys   1 

la^^ng   a  lower  specific   grav 

gravity  than  the 

mean  of  their 

than   the   mean   of  their 

components. 

components. 

Gold 

and 

Zinc. 

Gold 

and         Silver. 

" 

tt 

Tin. 

" 

"           Iron. 

It 

tt 

Bismuth. 

" 

"          Lead 

ti 
ti 

It 
tt 

Antimony. 
Cobalt. 

tt 

"          Copper. 
"           Iridium 

Silver 

" 

Zinc. 

tt 

"          Nickel. 

ti 

" 

Lead. 

Silver 

"          Copper 

tc 

tt 

Tin. 

Copper 

"          Lead. 

it 

it 

Bismuth. 

Iron 

"          Bismuth. 

It 

it 

Antimony. 

ti 

"          Antimony. 

Copper 

it 

Zinc. 

it 

"          Lead. 

li'^ 

tt 

Tin. 

Tin 

"          Lead. 

tt 

it 

Palladium. 

" 

"           Palladium. 

tt 

tt 

Bismuth. 

it 

"          Antimony. 

ti 

It 

Antimony. 

Nickel 

"          Arsenic. 

Lead 

tt 

Bismuth 
Antimony. 

Zinc 

"          Antimony. 

Platinum 

ti 

Molybdenum. 

' 

Palladium 

tt 

Bismuth. 

1  British  } 

Lssociati 

on  Reports,  1863,  p. 

97. 

3  Phillips'  Metallurgy. 

104     METALS  AND  ALLOYS   IISKI)  IX   PROSTHETIC  DENTISTRY. 

It  is  common  among  authorities  who  pubhsh  determinations  upon 
specific  gravities  of  the  alloys  to  give  the  calculated  as  well  as  the  ob- 
served .sj)eciHc  gravity. 

The  Color. — The  color  of  an  alloy  usually  resembles  that  of  the  metal 
which  predominates.  Some  few  exceptions  are  (juite  notable;  for 
instance,  gold  2  to  6,  and  silver  1  part  produces  an  alloy  of  a  greenish 
color,  and  it  is  said  that  -^j  part  of  silver  is  sufficient  to  modify  the 
color  of  gold.  Nickel  and  copper  form  alloys  varying  from  copper- 
red  to  the  bluish-white  of  nickel.  With  a  content  of  30  per  cent,  of 
nickel  the  alloy  is  silver  white;  while  with  zinc,  copper  yields  a  variety* 
of  shades,  from  the  silver  white  of  brass  consisting  of  copper  43,  and 
zinc  57  parts,  to  that  of  red  brass,  which  contains  80  per  cent,  or  more 
of  cop])er. 

Malleability,  Ductility,  and  Tenacity. — These  properties  are  generally 
very  much  modified  by  alloying.  As  a  rule  the  malleability  and  duc- 
tility are  decreased,  even  when  two  malleable  and  ductile  metals,  such 
as  gold  and  lead,  are  alloyed  together — a  very  small  content  of  lead 
destroying  the  malleability  and  ductility  of  the  noble  metal.  Again, 
copper  94  and  tin  6  parts  form  an  exceedingly  brittle  alloy.  Generally 
the  ductility  decreases,  while  the  hardness  as  compared  with  that  of 
the  constituent  metals  increases  to  a  considerable  extent;  for  example, 
gold  and  platinum,  two  very  ductile  and  soft  metals,  afford  an  alloy 
much  harder  and  of  greater  elasticity  than  either.  Gold  and  silver, 
being  too  soft  for  currency,  are  alloyed  with  10  per  cent,  of  copper, 
which  gives  them  the  required  hardness.  A  few  metals,  antimony, 
for  instance,  possess  the  property  of  making  metals  harder.  IVIr.  INIakins 
states  that  y^WiJ  P^^^  of  this  brittle  metal  will  make  gold  quite 
unworkable.  As  a  rule,  a  brittle  and  a  ductile  metal  afford  a  brittle 
alloy;  yet  copper  and  zinc  yield  a  malleable  and  ductile  alloy  in  brass. 

The  tenacity  is  generally  very  much  increased,  as  is  shown  by  the 
following  results  of  Matthiessen's  experiments.  Wires  of  the  same 
gauge  were  employed,  and  the  weights  causing  their  rupture  before 
and  after  alloying  noted  as  follows: 


Copper,  unalloyed 

Tin, 

Lead,  " 

Gold,  " 

Silver,  " 

Platinuni,  " 

Iron,  " 


Pounds  at  rupture. 
25  to  30 
under  7 
"  7 
20  to  25 
45  "  50 
.  45  "  50 
80   "   90 


Copper,  alloyed  with  12  per  cent.  Tin    . 

Tin,  "  "     "  "  Copper 

Lead,  "  "     Tin     . 

Gold,  "  "     Copper 

Silver,  "  "     Platinum 

Steel  (iron  compounded  with  carbon)     . 


Pounds  at  rupture. 

80  to  90 

7 

7 

70 

75  to  80 

.     above  200 


ALLOYS.  105 

Fusibility. — The  fusing  point  of  an  alloy  i.s  always  lower  than  that  oi 
the  least  fusible  metal  entering  into  its  eomposition,  and  is  .sometimes 
lower  than  that  of  any  of  the  components.  Thus  an  alloy  composed 
of  10  parts  lead  and  4  parts  tin  fuses  at  470°  F.,  melting  lower  than  the 
less  fusible  lead  (()17°  F.),  but  at  a  greater  tem])erature  than  tin  (442° 
F.);  and  an  alloy  composed  of  4  parts  lead,  2  parts  tin,  5  to  8  parts 
bismuth,  and  1  to  2  parts  cadmium  (Wood's  metal)  melts  at  140°  to 
161°  F.,  lower  than  that  of  any  of  its  constituents — tin  being  the  most 
fusible  (442°  F.).  Alloys  of  lead  and  silver,  containing  a  small  f[uantity 
of  the  latter,  are  more  fusible  than  lead,  and  sodium  and  potassimn 
form  an  alloy  fluid  at  ordinary  temperatures. 

jNIatthiessen^  explains  why  the  fusing  point  of  alloys  is  uniformly 
lower  than  the  mean  of  those  of  their  constituents:  "It  is  generally 
admitted  that  matter  in  the  solid  state  exhibits  excess  of  attraction 
over  repulsion,  while  in  the  liquid  state  these  forces  are  balanced,  and 
in  the  gaseous  state  repulsion  predominates  over  attraction.  Let  us 
assume  that  similar  particles  of  matter  attract  each  other  more  power- 
fully than  dissimilar  ones  attract  each  other.  It  will  then  follow  that 
the  attraction  subsisting  between  the  particles  of  a  mixture  will  be 
sooner  overcome  by  repulsion  than  will  the  attraction  in  the  case  of  a 
homogeneous  body;  hence,  mixtures  should  fuse  more  readily  than 
their  constituents." 

Sonorousness. — This  property  is  most  wonderfully  developed  in  some 
instances  by  alloying.  Copper  and  tin,  two  metals  wdiich  possess  the 
quality  in  but  a  small  degree  comparatively,  unite  to  form  an  alloy 
known  as  "bell  metal." 

Conductivity. — The  property  of  conductivity,  either  for  electricity  or 
heat,  in  an  alloy  is  much  inferior  to  that  of  the  pure  metals.  Advan- 
tage is  taken  of  the  high  electric  resistance  in  some  of  the  alloys, 
such  as  German  silver,  for  measuring  the  resistance  of  long  lines  of 
telegraph  wire,  the  electromotive  force  or  working  power  of  batteries, 
for  making  rheostats  and  other  apparatus  for  controlling  the  electric 
current,  etc. 

Decomposition. — Heat  decomposes  alloys  containing  volatile  metals 
like  mercury  or  zinc.  It  requires  a  temperature  much  above  the  boil- 
ing point  of  the  metal,  however,  to  completely  separate  all  traces  of  it 
from  an  alloy,  and  in  most  instances  this  cannot  be  accomplished  even 
then  without  the  assistance  of  chemical  agency.  When  gold  is  con- 
taminated with  tin,  the  latter  cannot  be  removed  entirely  by  roasting; 
but  if  heated  with  small  quantities  of  potassium  nitrate,  wliich  serves 
to  oxidize  the  base  metal,  it  may  be  entirely  removed.  Mercury  may 
be  completely  separated  by  roasting;  it  volatilizes  at  about  675°  F. 
When  endeavoring  to  expel  it  from  old  amalgam  fiUings,  however, 
the  mass  should  be  heated  bright  red. 

Annealing  and  Tempering. — AnneaHng  is  a  process  employed  in  the 
the  w^orking  of  various  metals  and  alloys  to  reduce  the  observed  brittle- 
ness  and  stiffness  which    result  from  the   change  of  molecular  struc- 

1  Makins'  Metallurgy,  p.  65. 


106     METALS  AND   ALLOYS   USED   L\  PROSTHETIC  DENTISTRY. 

ture,  produced  by  liammcriii<^,  loii<i;-continued  vibration,  rolling,  or 
sudden  cooling.  Ik'U  metal  is  brittle,  and  cracks  under  the  hammer, 
cold  a,s  well  a-s  heated.  If  it  be  repeatedly  brought  to  a  dark-red  heat 
and  (juickly  cooled  by  immersion  in  water,  its  brittleness  is  so  far 
decreased  that  it  can  be  hammered  and  stamped. 

The  dentist,  in  swaging  a  flat  sheet  of  gold  alloy  to  conform  to  his 
dies,  must  stop  at  intervals  and  anneal  the  piece  of  metal  to  prevent 
its  splitting  under  his  blows  and  pressure. 

It  is  said  sudden  changes  of  temperature  have  the  effect,  almost 
invaria})ly,  of  rendering  metals  brittle,  (jold,  silver  and  platinum, 
should  be  heated  for  a  re-arrangement  of  their  molecular  structure 
and  allowed  to  cool  slowly.  Lead,  tin,  and  zinc  are  annealed  by  im- 
mersion in  water,  which  is  then  made  to  l)oil  and  cool  slowly.  Steel 
should  not  be  annealed  in  an  open  fire,  as  the  carbon  which  enters  the 
iron  as  an  element  combines  with  the  oxygen  of  tlie  air  to  the  detri- 
ment of  the  steel. 

Oxidation. — Alloys  are  usually  more  easily  oxidized  than  their  con- 
stituents. Mr.  Makins^  says:  "The  superior  oxidizability  of  one 
constituent  of  an  alloy  appears  to  be  assisted  by  galvanic  action  set 
up.  This  is  always  the  case  where  an  electro-negative,  or  acid-forming 
metal,  is  alloyed  with  an  electro-positive,  or  base-producing  one.  Chem- 
ical action  is,  therefore,  generally  more  energetic  on  an  alloy  than  upon 
a  simple  metal;  and,  indeed,  metals  which  when  unalloyed  are  unaf- 
ected  by  an  acid,  will  be  acted  upon  by  the  same  acid  when  alloyed 
with  another  metal  which  is  soluble  in  the  acid  employed.  Thus  plati- 
num is  cjuite  insoluble  in  nitric  acid,  but  if  it  be  alloyed  with  a  large 
proportion  of  silver,  it  will  be  dissolved  with  the  silver  by  the  nitric 
acid,  and  that  to  the  extent  of  a  tenth  of  the  weight  of  silver." 

Nearly  all  metals  in  a  state  of  fusion  have  a  tendency  to  dissolve  a 
greater  or  less  amount  of  their  oxides;  and  this  is  particularly  true  of 
alloys,  as  then  the  metals  are  in  a  state  of  solution,  a  condition  most 
favorable  to  chemical  change,  A  striking  illustration  of  this  came 
untler  the  author's  notice  in  a  dental-amalgam  alloy  prepared  by  Dr. 
S.  E.  Knowles,  consisting  of  2  parts  tin  and  1  part  each  of  silver  and 
aluminum.  There  was  no  exceptional  difficulty  in  thoroughly  blend- 
ing the  constituents,  and  the  alloy  resembled  the  ordinary  dental- 
amalgam  alloy  when  comminuted  and  ready  for  mercury,  but  upon 
the  addition  of  mercury  the  oxidation  of  the  whole  was  so  rapid  that 
a  very  considerable  heat  was  evolved,  and  so  complete  that  nothing 
remained   but  a  black  stain. 

The  best  preventive  against  this  formation  of  oxides  and  their 
subsequent  absorption  is  to  protect  the  molten  alloy  by  a  layer  of  pul- 
verized charcoal  or  some  of  the  fluxes.  A  reduction  of  much  of  the 
oxide  formed  may  be  effected  by  vigorous  stirring  with  a  stick  of  green 
wood.  The  careful  addition  of  not  more  than  YTnr¥  ^^  T¥To  P^rts  of 
phosphorus  has  been  found  an  excellent  agent  for  the  deoxidation  of 
the  oxides  dissolved  in  bronze. 

•  Makins'  Metallurgy,  p.  64. 


ALLOYS.  107 

Zinc  and  the  alloys  used  in  the  dental  laboratory  for  making  dies, 
after  repeated  melting  and  casting  in  contact  with  the  air,  often  become 
thick  and  pasty  from  dissolved  oxides;  and  their  valuable  working 
qualities  are  so  seriously  impaired  that  they  fail  to  copy  the  fine  lines 
of  the  mold  and  produce  a  perfect  die.  Their  properties  may  be 
restored  to  some  extent  by  melting  under  pulverized  charcoal  or 
tallow,  and  vigorously  stirring  with  a  stick  of  green  wood,  or  by  dis- 
solving in  the  molten  metal  a  small  quantity  of  aluminum. 

Influence  of  Certain  Metals  in  Alloys. — (Vrtain  metals  when  present 
in  an  alloy  confer  upon  it  definite  properties  which  are  in  many  instances 
characteristic;  thus,  in  a  general  way,  mercury,  cadmium,  and  bismuth 
increase  fusibility;  tin,  hardness  and  tenacity;  antimony  and  arsenic, 
hardness  and  brittleness. 

Solder. — A  solder  is  an  alloy  or  metal  used  for  cementing  or  binding 
metallic  surfaces  or  margins  together,  and  the  process  is  usually  effected 
by  heat.     Ordinary  solders  may  be  hard  or  soft. 

The  Hard  Solders  comprise  those  whfch  require  a  red  heat  for 
their  melting. 

The  Soft  Solders  are  those  used  by  plumbers  and  tinsmiths,  and 
consist  principally  of  lead  and  tin,  with  sometimes  an  addition  of 
bisnuith. 

Brazier's  Solder,  for  uniting  the  surfaces  of  copper,  brass,  etc.,  is 
usually  composed  of  copper  and  zinc,  nearly  equal  parts,  with  a  small 
addition  of  tin,  and  sometimes  antimony. 

Silver  is  the  proper  solder  for  German-silver  articles,  and  gold  or  an 
alloy  of  gold  and  platinum  for  platinum. 

In  soldering,  the  surfaces  or  edges  to  be  united  must  be  kept  free 
from  oxidation  and  dirt.  To  keep  them  unoxidized  during  the  opera- 
tion several  fluxes  are  used,  such  as  dehydrated  borax,  or  some  of  the 
reliable  prepared  compounds  on  the  market  for  gold,  silver,  brass, 
or  copper  soldering;  rosin,  or  a  solution  of  zinc  chloride,  for  tin  plate; 
zinc  chloride  for  zinc,  and  rosin  and  tallow  for  lead  and  tin. 

Among  the  requirements  of  a  good  gold  solder  the  most  important 
are  carat,  color,  strength,  and  fusing  point.  In  fineness  it  should  be 
equal,  or  nearly  equal,  to  the  plate,  its  color  and  strength  as  near 
as  possible  the  same,  wdiile  the  fusing  point  should  be  a  trifle  lower — 
the  nearer  the  melting  point  of  the  plate,  the  better  the  results. 

To  obtain  these  qualities  it  is  necessary  to  prepare  a  solder  by  the 
addition  of  some  metal  which  will  fuse  at  a  lower  temperature  than 
any  of  the  various  parts  of  the  plate.  Zinc  is  admirably  suited  for  this 
purpose,  and  is  generally  used,  since  it  permits  of  a  solder  as  fine,  or 
nearly  as  fine,  as  the  plate.  In  addition  to  this  it  also  possesses  the 
advantage  of  yielding  a  more  fluid  solder  than  copper  and  silver,  per- 
mitting it  to  flow  very  freely.  On  account  of  the  oxidation  or 
volatilization  which  takes  place,  it  is  observed  that  any  subsequent 
fusing  requires  a  greater  heat.  An  advantage  is  also  obtained  in 
this  fact,  since  it  enables  more  perfect  second  solderings  with  the 
same  alloy. 

The  process  of  soldering  is  a  cementation  by  superficial  alloying, 


108     MIITALS  A.\I>   ALLOYS    JISKD   IN  PROSTHETIC  DENTISTRY. 

and  is  admirably  illustrated  in  the  operation  of  soldering  platinum  bases 
with  pure  gold  for  eontinuous-gum  dentures.  By  means  of  the  blow- 
pipe the  gold  is  Howed  over  the  platinum  surfaces  thus  joining  them. 
If  the  joint  is  not  well  made,  and  an  intervening  space  is  hllcd  with 
gold,  this  is  not  as  strong  as  a  close  joint.  This,  however,  is  all  reme- 
(lied  during  the  process  of  baking  the  body  and  enamel,  as  the  high 
heat  re(juire(l  for  this  so  diminishes  the  cohesive  power  of  the  platinum 
that  it  readily  and  completely  alloys  with  the  gold,  producing  a  strongei 
joint  of  a  platinum-gold  alloy,  which  is  observed  to  be  the  same  color 
as  the  platinum. 

Autogenous  Soldering  is  a  process  of  soldering  by  direct  fusion  of 
the  contiguous  parts,  without  the  intervention  of  a  more  fusible  alloy. 
It  is  extensively  wsvd  'n\  uniting  ends  of  bands  for  collar  crowns. 

Preparation  of  Alloys. — This  would  seem  to  be  a  simple  1task,  but 
in  order  to  produce  an  accurate  result  it  is  far  from  being  as  easy  as  it 
may  seem.  INIost  alloys  are  prepared  by  directly  melting  the  metals 
together,  but  much  skill,  judgment,  and  experience  are  refjuired  to 
determine  when  it  is  best  to  add  each  constituent,  and  the  amount  of 
each  to  be  used,  to  protect  the  molten  mass,  and  to  handle  it  generally. 

The  metal  having  the  highest  fusing  point  is  generally  melted  first, 
and  the  others  are  added  in  the  reverse  order  of  their  fusibility. 

The  varying  densities  of  the  metals  to  be  combined  frefjuently  ren- 
der the  formation  of  a  homogeneous  mass  very  difficult.  In  some 
instances  the  heavier  metal  tends  to  sink  to  the  bottom,  carrying  with  it 
a  small  cjuantity  of  the  other,  while  the  lighter,  floating  above,  retains 
a  small  quantity  of  the  heavier.  For  instance,  only  a  small  proportion 
of  zinc  will  unite  with  lead,  or  aluminum  with  bismuth;  but,  as  a  rule, 
metals  mix  perfectly  in  the  fluid  state.  AMien,  however,  the  fluid  mix- 
ture is  poured  into  the  ingot  mold,  it  rarely  happens  that  the  solidified 
mass  is  perfectly  homogeneous.  The  reason  of  this  is  that  the  addition 
of  one  metal  to  another  produces  an  alloy,  the  solidifying  point  of  which 
is  usually  lower  than  it  should  be  according  to  calculations  based  upon 
the  proportionate  amounts  and  fusing  points  of  the  constituents.  One 
particular  mixture  has  a  lower  fusing  point  than  any  other  possible 
mixture  of  the  metals  employed,  and  this  is  termed  the  eutectic  alloy 
of  that  series.  Aside  from  those  possibly  true  chemical  combinations 
of  metals,  a  fluid  mixture  of  two  metals  may  be  expected  to  begin  depos- 
iting its  less  fusible  constituent  first,  and,  as  the  temperature  falls,  more 
and  more  of  this  element  will  be  separated,  the  other  constituent  con- 
centrating in  the  fluid  residue  until  this  has  ac(juired  the  eutectic  com- 
position, when  it  will  solidify  as  a  whole  in  the  spaces  left  between  the 
already  solidified  particles.  The  more  slowly  the  material  solidifies, 
the  more  marked  will  be  the  separation  that  occurs.  To  obtain  as 
homogeneous  an  alloy  as  possible,  the  metals,  while  in  a  state  of  fusion, 
must  not  be  allowed  to  remain  quiescent,  but  an  intimate  mixture 
effected  by  vigorous  stirring,  sticks  of  dry,  soft  wood  being  used  for 
the  purpose.  By  stirring  the  fused  mass  with  one  of  these  sticks  the 
wood  is  more  or  less  carbonized  according  to  the  temperature  of  the 
mass,  gases  are  evolved  from  the  carbonizing  wood,  which,  by  ascend- 


ALLOYS.  109 

ing  in  the  fused  mass,  contribute  to  its  intimate  mixture.  The  stirring 
should  continue  for  some  time  and  the  alloy  then  cooled  a,s  rapidly  as 
possible. 

For  preparing  alloys  in  a  small  way  a  crucible  is  used,  and  the  alloy 
is  covered  with  a  suitable  flux  to  protect  it  from  the  action  of  atmos- 
pheric air.  Four  sources  of  loss  must  be  guarded  against:  (1)  loss  by 
oxidation;  (2)  loss  by  volatilization;  (3)  loss  by  chemical  combination 
with  the  flux;   (4)  loss  by  fracture  or  solution  of  the  crucible. 

The  first  may  be  prevented  by  the  use  of  one  of  the  various  fluxes, 
or  covering  the  surface  with  pulverized  charcoal.  The  second  loss 
usually  occurs  through  an  endeavor  to  alloy  a  metal  of  a  high  fusing 
point  with  one  which  fuses  at  a  low  temperature.  Under  such  circum- 
stances the  one  requiring  a  high  temperature  should  be  fused  first  and 
well  covered  with  flux  melted  to  extreme  fluidity;  the  more  fusible 
metal  should  then  be  added  in  as  large  a  piece  as  convenient  and  quickly 
thrust  beneath  the  molten  surface.  The  third  source  of  loss  is  princi- 
pally caused  by  the  use  of  borax  as  a  flux  for  some  base  metals.  It  is 
well  known  that  in  much  borax  a  portion  of  the  boric  acid  is  not  per- 
fectly saturated,  and  this  is  especially  true  of  the  prepared  article;  and 
if  melted  with  some  base  metals  the  free  acid  is  absorbed,  which,  with 
the  sodium  borate,  forms  double  salts  of  a  glassy  nature.  Hence,  by 
fusing  some  metals  and  alloys  under  borax,  a  certain  portion  will  be 
lost  in  chemical  combination.  The  fourth  cause  is  guarded  against 
by  careful  selection  of  crucibles.  If  alloys  of  low  fusing  metals  are  to 
be  made,  the  ordinary  clay  or  Hessian  crucible  is  all  that  is  necessary, 
and,  indeed,  with  proper  care,  noble  metals  may  be  alloyed  in  it  with- 
out danger  of  loss;  but  it  is  liable  to  perforation  by  corrosive  fluxes, 
allowing  the  molten  alloy  to  escape.  Therefore,  for  the  preparation  of 
expensive  alloys  from  noble  metals,  the  employment  of  tried  graphite 
or  graphite  and  clay  crucibles  often  saves  much  trouble  and  expense. 

In  some  instances,  especially  when  metals  are  known  to  form  chem- 
ical combinations,  it  may  be  best  to  melt  the  one  of  lowest  fusing  point 
first,  and  then  dissolve  the  other  components  in  it.  Or,  those  of  low 
fusing  point  may  be  melted  in  one  crucible,  while  those  more  difficult 
of  fusion  are  melted  in  another,  then  combined  in  the  molten  state. 

"]Many  alloys,"  says  INIr.  Brannt,^  "possess  the  property  of  chang- 
ing their  nature  by  repeated  remelting,  several  alloys  being  formed  in 
this  case,  which  show  considerable  dift'erences,  physically  as  well  as 
chemically.  The  melting  points  of  the  new  alloys  are  generally  higher 
than  those  of  the  original  alloy,  and  their  hardness  and  ductility  are 
also  changed  to  a  considerable  extent.  This  phenomenon  is  frequently 
connected  with  many  evils  for  the  further  application  of  the  alloys, 
and  in  preparing  alloys  showing  this  property  the  fusion  of  the  metals 
and  subsequent  cooling  of  the  fused  mass  should  be  effected  as  rapidly 
as  possible." 

Although  most  of  the  heavier  metals  are  at  present  used  in  the  prep- 
aration of  alloys,  copper,  zinc,  tin,  lead,  silver,  and  gold  are  more  fre- 

1  MetalHc  Alloys,  p.  87. 


no     METALS  AM)   ALLOYS   USED   L\   PROSTHETIC  DEyTISTRY. 

quently  employed  than  all  others.  Alloys. eontaining  nickel  have  become 
of  great  importance  as  well  as  those  in  which  alumiiunu  is  a  con- 
stituent. 

Mr.  IJrannt  reconuneiids  for  experimeiitution  that  metals  be  added 
to  each  other  in  certain  quantities  by  weight,  that  is,  according  to  their 
atomic  weights,  and  claims  that  in  this  manner  alloys  of  determined, 
charact(M"istic  propertifvs  are,  as  a  rule,  produced;  or,  if  such  does  not 
answer  the  demands  of  the  alloy,  the  object  may  be  obtained  by  taking 
two,  three,  or  more  e(|uivalents  of  the  metal,  exception  being  made  in 
the  cases  of  arsenic  and  such  elements. 


GOLD. 

Aurum.  Symbol,  Au. 

Atomic  weight,  195.7.  Malleability,  first  rank. 

Melting  point,  1100°  (2012°  F.).  Tenacity,  fifth  rank. 

Ductility,  first  rank.  Specific  gravity  (cast),  19.265. 

Conductivity  (heat),  53.20.  Conductivity  (electricity),  77.96. 

(Silver  being  100.) 

Occurrence. — Gold  is  found  in  nature  chiefly  in  the  metallic  state, 
or  as  native  gold,  and  less  frequently  in  combination  with  tellurium, 
lead,  and  silver.  It  is  also  found  combined,  or,  perhaps,  more  strictly 
speaking,  minutely  mixed  with  pyrites  and  other  sulphides,  more  com- 
monly called  "sulphurettes." 

Native  Gold  occurs  rather  frecjuently  in  crystals  belonging  to  the 
cubic  system,  the  octahedron  being  the  commonest  form,  but  other 
and  complex  combinations  have  been  observed.  Large  crystals  are 
rarely  well  defined,  owing  to  the  softness  of  the  metal,  the  points  being 
commonly  rounded.  The  most  characteristic  forms,  however,  are  the 
nuggets  or  pepites.  These,  when  of  a  weight  less  than  one-quarter  to 
one-half  an  ounce,  are  known  as  gold  dust. 

Except  the  larger  nuggets,  which  are  usually  more  or  less  angular 
or  irregular,  gold  is  generally  found  in  a  bean-shaped  or  somewhat 
flattened  form,  the  smallest  particles  being  scales  of  scarcely  appre- 
ciable thickness,  and  owing  to  their  small  bulk,  as  compared  with 
their  surface,  they  are  frequently  suspended  in  water  and  may  be  washed 
away  by  a  rapid  current;  hence,  they  are  known  as  float  gold. 

In  the  museum  of  the  Mining  Bureau  in  San  Francisco  are  several 
plaster-of-Paris  models  of  famous  gold  nuggets  found  in  the  various 
gold  regions  of  the  world.  The  largest  single  piece  of  gold  ever  found 
was  taken  out  at  Ballarat,  Victoria,  Australia.  It  weighed  2166  troy 
ounces,  and  was  valued  at  $41,882.  The  second  largest  was  discovered 
in  the  Ural  Mountains  district,  and  weighed  1200  ounces.  The  third 
largest,  which  was  also  found  in  Victoria,  Australia,  weighed  1121 
ounces,  and  was  valued  at  .$22,000. 

The  physical  properties  of  native  gold  are  c|uite  similar  to  those  of 
the  melted  metal  and  its  alloys.  The  composition  varies  considerably 
in  different  localities,  as  shown  in  the  following  table: 


GOLD. 


Ill 


Analysis  of  Native  Gold  from  \ 

.VHIUUS 

LOC.VLITIKS. 

Locality. 

Gold. 

Silver. 

Iron. 

Cijpper. 

Europe  : 

British  Isles — 

\'igra  and  Clogau 

.     90.16 

9.26 

Trace. 

Trace. 

Wicklow  (River)    . 

,     92.32 

6.17 

0.78 

Transylvania 

.      60.49 

38.74 

0.77 

Asia  : 

Russian  Empire — 

Brezovsk 

.      91.88 

8.03 

Trace. 

0.09 

Ekaterinburg 

.     98.96 

0.16 

0.05 

0.35 

Africa  : 

Ashantee 

.      90.05 

9.94 

America  : 

Brazil  . 

.      94.00 

5.85 

Central  America    . 

.     88.05 

11.96 

Titiribi 

.     76.41 

23.12 

0.87 

California 

.     90.12 

9.01 

iVIariposa 

.     81.00 

18.70 

Cariboo 

.     84.25 

14.90 

0.03 

Australia  : 

South  Australia 

.     87.78 

6.07 

6.15 

Ballarat 

.      99.25 

0.65 

The  most  important  minerals  containing  gold  are: 

Sylvanite,  or  graphic  tellurium ,  (AgAu)Te2,  containing  24  to  26 
per  cent. 

Calaverite,  AuTcj,  containing  42  per  cent. 

Nagyagite,  or  foliate  tellurium,  of  a  complex  and  rather  indefinite 
composition,  and  containing  from  5  to  9  per  cent,  only  of  gold. 

The  calaverite,  a  nearly  pure  telluride  of  gold,  has  been  found  to 
some  considerable  extent  in  Calaveras  County,  California. 

The  minerals  of  the  second  class,  called  auriferous,  are  compara- 
tively numerous,  and  include  many  of  the  metallic  sulphides.  The 
most  important  of  these  are  iron  pyrites  and  galena;  the  first  of  these 
is  of  great  practical  importance,  being  found  in  many  districts  exceed- 
ingly rich,  and  next  to  the  native  metal,  is  the  most  prolific  source  of  gold. 

A  Native  Amalgam  of  gold  is  found  in  California,  but  rarely  in  any 
considerable  quantities. 

Gold  is  so  widely  distributed  throughout  the  earth's  crust  that  few 
regions  may  be  said  to  be  destitute  of  slight  traces  of  it ;  yet  it  has  been 
found  in  comparatively  few  localities  in  quantities  sufficient  for  econom- 
ical extraction.  The  principal  supplies  of  the  metal  have  been  derived 
from  Africa,  California,  Australia,  Mexico,  Brazil,  Ural  Mountains, 
Transylvania,  Alaska,  etc. 

The  association  and  distribution  of  gold  may  be  considered  under 
two  different  heads,  namely,  as  it  occurs  in  mineral  veins,  and  in  alluvial 
or  other  superficial  deposits  which  are  derived  from  the  waste  or  disin- 
tegration of  the  former.  As  regards  the  first,  it  is  usually  found  in 
quartz  veins  or  reefs  transversing  slaty  or  crystalline  rocks,  either  alone 
or  associated  with  such  metals  as  iron,  copper,  tellurium,  and  rarely 


112     MIITALS  ASI)  ALLOYS    VSKD   L\   PROSTHETIC  DENTIS'IRY. 

bismuth,  or  sucli  iniiuTuls  ;i,s  inagiu'tio  and  arsenical  pyrites,  galena, 
specular  iron  ore,  and  silver  ore,  and  rarely  with  the  sulj)liides  of  molyb- 
denum,  tungstate   of  calcium,    bismuth,   and   tellurium   minerals. 

In  the  second  or  alluvial  class  (placers)  of  deposits  it  is  associated 
chieHy  with  those  minerals  of  great  density  and  hardness,  such  as 
platinum,  iridum,  and  other  metals  of  the  platinum  group,  tinstone, 
chromic,  magnetic,  and  brown  iron  ores,  diamond,  sapphire,  ruby, 
topaz,  etc.,  which  re{)resent  the  more  durable  original  constituents  of 
the  rocks  whose  disintegration  has  furnished  the  detritus. 

Refining  Gold. — In  less  it  can  be  utilized  tlie  accumulation  of  gold 
in  the  form  of  scraps,  filings,  etc.,  in  the  dental  laboratory  and  operating 
room  frequently  becomes  a  source  of  considerable  loss  to  the  dentist, 
because  he  is  not  familiar  with  the  methods  of  refining  or  lacks  the 
necessary  apparatus. 

Some  forms  of  scrap  gold,  such  as  old  fillings,  need  only  to  be  melted 
with  the  proportion  of  silver,  copper,  or  both,  to  produce  the  desired 
alloy.  Others,  as  scrap  plate  of  know-n  carat,  may  be  utilized  by  simply 
remelting  and  rolling. 

Old  crowns,  plates,  l)ridges,  mixed  filings  containing  more  or  less 
iron  from  the  file,  zinc,  lead,  antimony,  and  other  base  metals  may  be 
converted  into  malleable  gold  by  simply  roasting  with  such  fluxes  as 
will  combine  chemically  with  the  base  metals  and  remove  them. 

Sweepings  may  be  washed  and  then  carried  through  the  same  process 
which  is  known  as  "  roasting." 

The  Roasting  Process. — A  method  for  rendering  brittle  gold  malleable. 
This  process  may  be  most  satisfactorily  employed  where  the  approxi- 
mate carat  of  the  bulk  of  the  scraps  is  known  and  the  gold  is  suspected 
of  being  unworkable  because  of  the  admixture  of  l)ase  metals. 

The  larger  pieces  should  be  removed  from  the  accumulation  and 
the  smaller  ones  with  the  filings  freed  from  as  much  iron  and  steel  as 
possible  by  a  good  magnet.  AH  should  then  be  placed  in  a  previously 
well-boraxed  and  tested  graphite  crucible,  with  the  addition  of  sufficient 
potassium  carbonate  to  well  cover  the  charge;  the  ol)ject  of  this  addi- 
tion being  to  form,  when  heated,  a  thin  flux,  permitting  the  small  par- 
ticles and  filings  to  sink  and  accumulte  in  one  mass. 

The  furnace  should  be  placed  beneath  a  fume  chimney  or  by  a  win- 
dow with  an  outward  draught,  that  the  fumes  escaping  from  it  during 
the  roasting  may  not  fill  the  lal)orat()ry,  th('rel)y  endangering  the  health 
of  the  operator  and  damaging  such  instruments  and  t(»()ls  as  may  be 
unprotected.  The  most  convenient  place  to  avoid  such  results  is  the 
fireplace.  The  furnace  may  l)e  placed  beneath  its  chimney  in  such  a 
maimer  that  all  fumes  will  be  readily  c-arried  off. 

When  the  metal  has  become  thoroughly  fused,  the  refining  ])rocess  may 
be  begun  by  first  adding  small  quantities  of  the  oxidizing  agent,  potassium 
nitrate  (KNO^),  accompanied  with  borax,  as  needed  to  properly  protect 
the  mass  and  further  the  process.  The  object  of  the  potassium  nitrate 
is  to  furnish  sufficient  oxygen  to  oxidize  the  contaminating  base  metals 
beneath  the  flux,  thus  se})arating  them  from  the  gold.  As  most  base 
metals  are  easily  oxidized  under  these  circumstances,  a  continuation  of 
this  process  from  ten  minutes  to  one  hour  and  a  half,  according  to  the 


GOLD.  113 

quantity  of  material,  and  the  proportion  of  base  metals  eontained,  add- 
ino;  the  nitrate  and  ])()rax  as  re(|uired,  and  maintaining  a  state  of  perfect 
fusion  of  the  metal,  tiie  ingot,  when  made  by  pouring  into  a  previously 
warmed  and  oiled  mold,  will  be  found  to  be  quite  malleable. 

If,  however,  upon  examination  it  is  found  to  be  still  brittle,  it  sliould 
be  plaeed  in  a  clean,  boraxed,  and  tested  crucible,  heated,  and  brought 
to  a  perfect  state  of  fusion.  A  mixture  of  ecjual  parts  of  finely  pul- 
verized vegetable  charcoal  and  ammonium  chloride  should  then  be 
added;  at  first  sufficient  to  properly  cover  and  protect  the  molten  mass 
and  afterward  a  small  quantity  at  a  time  as  it  is  needed.  "When  the 
metal  has  been  sufficiently  treated,  which  may  be  determined  by  remov- 
ing small  quantities  and  subjecting  them  to  the  physical  tests  for  mal- 
leability, the  crucible  is  to  be  removed  from  the  furnace  and  the  metal 
cast  into  an  ingot  or  allowed  to  cool  in  the  crucible  as  a  button.  The 
rationale  of  such  a  process  is  that  the  heat  of  the  crucible  breaks  up 
the  chloride  compound,  liberating  the  chlorine  in  the  nascent  state; 
which  in  turn  combines  with  the  metals  lead,  tin,  and  silver  contained 
in  the  gold  to  form  their  respective  chlorides.  These  are  either  volatilized 
or  taken  up  by  the  flux,  the  gold  remaining  free  of  them. 

IMercuric  chloride  is  sometimes  used  when  the  contamination  of  the 
gold  with  lead  or  tin  is  extensive,  or  where  it  is  desired  to  remove  a 
quantity  of  silver.  But  its  use  is  so  dangerous  on  account  of  the  fumes 
evolved  it  is  rarely  employed. 

Sulphur  or  antimonic  sulphide  is  used  to  abstract  large  quantities 
of  silver  from  gold,  by  combining  with  the  former  to  form  the  fusible 
sulphide  of  silver,  leaving  the  gold  free,  or  if  the  antimonic  sulphide 
has  been  used,  contaminated  with  antimony,  which  may  be  removed 
by  fusing  with  borax  and  potassium  nitrate,  as  previously  described. 

In  the  process  of  refining  by  fluxes,  the  first  step  should  be  to  deter- 
mine, as  far  as  possible,  the  nature  of  the  debasing  elements;  this  being 
known  or  reasonably  approximated,  the  process  may  be  confined  to 
the  particular  flux  most  likely  to  free  the  gold  from  its  contamination. 
Iron,  steel,  zinc,  copper,  antimony,  and  bismuth  are  perhaps,  best 
removed  by  oxidation  through  the  agency  of  potassium  nitrate.  Lead, 
tin,  and  silver  are  removed  by  chlorine. 

If,  after  such  treatment,  the  alloy  is  found  to  be  malleable,  but  stiff 
or  elastic,  or  dull  in  color,  it  very  probably  contains  some  platinum 
which  cannot  be  removed  by  this  means,  but  which  may  be  gotten  rid 
of  by  a  wet  method.  When  desired,  such  an  alloy  may  be  made  direct 
use  of  as  clasp  gold. 

When  the  object  is  to  produce  pure  gold  from  which  to  subsequently 
prepare  desired  carats  by  alloying  the  results,  it  is  best  and  most  con- 
veniently attained  by  the  process  known  as  "  parting  gold." 

Parting  Gold. — A  wet  method  for  refining  gold  by  inquartation, 
or  "quartation,"  as  it  is  more  commonly  called,  is  known  as  the  process 
of  parting  gold.  This  is  accomplished  by  digesting  the  thinly  rolled 
or  granulated  alloy  of  silver  and  gold  in  either  nitric  or  sulphuric  acid. 

In  the  choice  of  metal  for  tliis  operation,  an  endeavor  should  be 
made  to  obtain  gold  containing  as  much  silver  as  possible,  and,  as  this 
8 


114     MKTM.S  AXD   ALLOYS    USED   fX  PROSTHETIC  DEyTlSTRY. 

will  rt'(juirc  an  additional  (jnantity  of  the  latter  metal  fused  with  it  in 
order  to  carry  out  the  operation,  it  is  of  course  an  object,  if  possible, 
to  employ  silver  which  contains  small  quantities  of  gold,  and  thus, 
to  carry  on  a  double  refining  process  at  once. 

As  the  actual  separation  of  the  two  is  effected  by  digesting  the  mix- 
ture in  hot  nitric  acid,  which,  while  it  is  a  ready  solvent  for  other  metals, 
is  inactive  upon  gold,  it  may  be  asked:  Why  not  at  once  treat  the  alloy 
with  acid  without  such  alloying?  Such  would  be  quite  useless,  for, 
the  foreign  metals  being  in  so  small  a  relative  proportion,  the  acid  would 
only  remove  the  alloy  at  or  near  the  surface,  the  metal  being  sufficiently 
close  in  texture  to  mask  all  the  rest  from  the  action  of  the  acid. 

The  sulphuric  acid  process  is  doubly  reconmiended,  especially  when 
large  quantities  of  the  alloy  are  to  be  digested,  as  it  is  less  expensive, 
and  the  gold  is  obtained  of  a  greater  degree  of  fineness.  The  oxidizing 
action  of  the  nitric  acid  is  of  especial  value,  however,  when  tin  or 
antimony  is  ])resent  in  the  batch  of  metal. 

Preparation  of  the  Alloy. — The  impure  gold  is  first  weighed  and  the 
approximate  weight  of  the  silver,  if  it  contains  any,  subtracted;  silver 
is  then  added  in  the  proportion  of  three  to  one,  less  the  amount  already 
contained  in  the  alloy,  thus  when  melted  forming  an  alloy  of  three 
parts  silver  and  one  part  impure  gold.  Hence  the  term  "quartation." 
These  proportions  are  then  fused  together  in  a  clean  and  boraxed  cruci- 
ble, well  mixed,  and  either  poured  into  warmed  and  oiled  ingot  molds, 
to  be  subsequently  rolled,  or  dropped  while  molten  from  the  crucible 
into  a  wooden  tub  or  tank  of  cold  water  for  the  purpose  of  granulation. 
The  latter  is  unquestionably  the  simplest  method  of  preparing  it  for 
the  digesting  process,  for,  if  poured  into  the  ingot  molds,  the  alloy  will 
require  rolling  to  a  very  thin  ribbon  (No.  35  gauge),  after  which  it 
must  be  cut  into  small  pieces.  Rolling  it  many  times  is  impossible 
because  the  gold  that  it  is  desired  to  refine  is  exceedingly  brittle. 
The  alloy  being  thus  prepared,  is  ready  for  the  acid. 

Nitric  Acid  Process. — Yov  this  process  the  prepared  alloy  is  placed 
in  a  Florence  flask  and  nitric  acid  to  the  amount  of  about  one  and  one- 
half  times  the  weight  of  the  alloy  poured  on.  The  acid  should  always 
be  tested  for  chlorine  by  adding  a  drop  of  a  solution  of  silver  nitrate 
(AgXOg)  to  it,  which,  if  chlorine  l)e  present,  will  instantly  be  rendered 
milky  from  the  precipitated  chloride  of  silver.  Ileat  the  flask  gently 
in  a  sand  bath  over  a  Bunsen  or  alcohol  flame.  Copious  red  fumes  of 
the  oxides  of  nitrogen  and  ammonium  will  be  given  off,  showing  vigor- 
ous action  on  the  alloy,  and  the  silver  and  other  metals  will  be  dissolved, 
leaving  the  gold  in  a  spongy  mass  of  a  blackish-])rown  color.  When 
this  evolution  has  entirely  ceased  and  the  flask  is  clear,  carefully  decant 
the  solution  of  the  nitrates  of  silver,  etc.,  thus  formed  and  preserve  it, 
adding  a  fresh  portion  of  nitric  acid  and  boil  until  all  fumes  cease  to 
rise,  which  marks  the  termination  of  the  digesting  process.  The  acid 
is  now  replaced  by  distilled  water  two  or  three  times,  for  the  purpose  of 
washing  the  gold  remaining.  At  length  filter  the  contents  of  the  flask, 
catching  the  gold  on  the  filter  paper,  add  a  sufficient  quantity  of  potas- 
sium carbonate,  fold  the  ])aper  over  the  whole,  and  ]>lace  in  a  previoush' 
boraxed  crucible,  melt  and  pour  into  warmed  and  oiled  ingot  molds. 


GOLD.  115 

Gold  thus  refined  may  reaeh  -{\;\f'(j  fineness,  and  is  ready  for  any 
desiraV)le  alloying. 

For  the  recovery  of  the  silver,  see  that  subje(t. 

Sulphuric  Acid  Process. — The  use  of  sulphuric  acid  for  the  operation 
is  preferred  by  many.  For,  as  was  stated,  it  is  more  economical;  and 
the  gold  so  refined  is  more  thoroughly  freed  from  silver;  indeed,  it  is 
said  that  gold  having  been  previously  refined  by  the  means  of  nitric 
acid  may  be  freed  of  still  more  silver  by  this  acid.  In  operating  the 
metals  are  so  mixed  that  the  gold  amounts,  at  most,  to  not  quite  half 
the  weight  of  the  silver;  and  if  copper  is  contained  (which  in  small  pro- 
portions facilitates  the  operation),  it  should  be  under  10  per  cent.,  for 
if  too  much  be  present,  a  large  quantity  of  sulphate  of  copper  will  be 
formed,  which  latter  is  insoluble  in  the  strong  acid  liquors.  The  process 
may  be  employed  for  silver  containing  very  small  cjuantities  of  gold 
Thus,  in  France,  it  was  found  very  profitable  to  separate  the  gold  from 
old  five-franc  pieces,  which  contained  only  Yihr  ^^  ToVo  ^f  gold. 

The  alloy  having  been  granulated,  as  before  described,  is  introduced 
into  a  digester  (Florence  flask)  with  about  two  and  one-half  times  its 
weight  of  concentrated  sulphuric  acid.  This  is  allowed  to  boil,  during 
which  strong  action  is  evidenced  by  copious  evolution  of  sulphur  dioxide, 
while  the  silver  and  copper  are  simultaneously  converted  into  sidphates. 
This  first  boiling  is  continued  as  long  as  sulphur  dioxide  is  evolved, 
which  in  large  quantities  of  metal  will  commonly  go  on  about  four 
hours.  The  liquid  is  then  removed  and  a  smaller  quantity  of  acid 
added,  the  boiling  being  further  carried  on  for  a  short  time,  after  which 
the  digester  is  allowed  to  remain  at  rest,  in  order  that  the  gold  may 
subside.  Sometimes  it  may  be  necessary  to  make  even  a  third  addi- 
tion of  acid. 

Repeated  washing  of  the  gold  with  boiling  water  is  now  necessary, 
as  the  sulphate  of  silver  is  a  very  insoluble  salt,  and  sulphate  of  copper, 
when  contained  in  so  acid  a  menstruum,  is  alsc  somewhat  so.  The 
gold  is  then  dried,  melted,  and  poured,  as  described  before. 

This  process  affords  gold  as  pure  as  f-ff^. 

The  Preparation  of  Chemically  Pure  Gold.— The  metal,  either 
in  the  form  of  powder,  granulations,  thin  plate,  or  "cornets"  from  the 
purest  gold  that  can  be  obtained,  is  dissolved  in  chemically  pure  nitro- 
hydrochloric  acid.^  The  best  material  to  operate  on  is  gold  which  has 
been  refined  in  the  ordinary  way;  this  may  be  used  in  the  form  of  a 
powder,  as  it  is  precipitated  in  the  last  process,  as  granulations  or  as 
plate.  The  acid  for  small  quantities  is  best  contained  in  an  evaporat- 
ing dish  placed  in  a  sand  bath  upon  a  tripod,  over  the  flame  of  a  Bunsen 
burner,  beneath  a  chimney  or  near  an  open  window.  The  action  will 
be  tolerably  energetic  when  the  metal  is  first  introduced;  hence,  it  is 
not  necessary  to  ignite  the  burner  at  the  start,  but  as  the  action  slackens 
a  moderate  heat  may  be  applied. 

Instead  of  previously  mixing  the  acids,  the  hydrochloric  acid  may 
first  be  poured  over  the  metal,  and  the  nitric  acid  afterward  gradually 
added  in  small  portions,  the  function  of  the  nitric  acid  being  to  oxidize 
the  hydrogen  of  the  hydrochloric  acid,  converting  it  into  water,  while 

1  Ooe  volume  of  nitric  to  two  of  hydrocbiloric  acid  (or  any  proportion,  so  the  latter  is  in  excess). 


116     METALS  AND  ALLOYS   USED  L\  PROSTHETIC  DENTISTRY. 

the  chlorine,  which  is  the  active  solvent,  is  Hl>erate(l  in  the  nascent  state 
and  unites  with  the  gold,  converting  it  into  auric  chloride,  which  dissolves. 

Each  ounce  of  gold  will  require  about  three  and  one-half  ounces  of 
mixed  acid  for  its  solution.  During  the  processs  of  solution  a  sediment 
will  be  noticed  in  the  bottom  of  the  evaporating  dish,  which  will  be 
recognized  by  the  operator  as  a  silver  chloride,  formed  by  the  union 
of  the  silver  contained  in  the  gold  and  the  liberated  chlorine.  It  must 
not  be  expected  that  all  the  silver  will  l)e  directly  precipitated  to  the 
bottom  as  a  chloride,  for  the  liquor  is  strongly  acid,  and  some  may  be 
held  in  solution.  Therefore,  this  must  be  taken  into  consideration, 
and  subsequent  pains  taken  to  throw  it  down  by  the  thorough  evapora- 
tion of  the  nitric  acid.  The  gold  having  been  dissolved,  the  solution 
is  now  best  transferred  to  a  clean  dish  bv  decantation,  leaving  the 
chloride  of  silver  in  the  first  and  the  solution  contained  in  the  second 
dish  heated  to  further  evaporate.  When  about  one-third  is  evaporated 
more  chloride  of  silver  will  be  found  to  have  been  separated  from  the 
solution  and  precipitated.  It  is  well,  therefore,  to  again  transfer  the 
solution  to  a  third  dish  by  decantation  and  evaporate  as  before,  care 
always  being  maintained  during  the  heating  not  to  apply  so  great  a 
temperature  as  to  decompose  the  auric  salt  which  adheres  to  the  sides 
of  the  dish  above  the  fluid. 

As  the  bulk  is  reduced  over  the  gentle  heat  by  evaporation,  small 
quantities  of  hydrochloric  acid  are  to  be  added  from  time  to  time,  which 
has  the  effect  of  liberating  nitrous  anhydride  by  decomposing  the  remain- 
ing nitric  acid  in  the  liquor;  these  additions  must,  however,  be  made 
very  cautiously,  for  the  action  produced  is  very  energetic,  and,  without 
due  precaution,  considerable  portions  of  the  now  rich  liquor  will  be 
thrown  out  of  the  dish  and  lost.  When  the  liquor  has  become  of  a  deep- 
red  color,  and  of  the  consistency  of  syrup,  it  is  to  be  withdrawn  from 
the  heat  and  permitted  to  rest  for  a  time,  when  the  whole  of  the  auric 
chloride  will  crystallize,  forming  a  mass  of  prismatic  crystals. 

The  bottom  of  the  dish  is  now  carefully  wiped  off  to  remove  any 
sand  or  dirt  that  may  have  collected  there  from  the  sand-bath,  and 
the  dish  and  its  contents  immersed  in  about  a  half  pint  of  distilled  water, 
acidulated  slightly  with  hydrochloric  acid.  It  is  better  now  to  let  this 
solution  stand  a  week,  for  chloride  of  silver,  although  slightly  soluble 
in  a  very  strong  and  hot  acid  solution,  is  separated  by  dilution,  and 
by  allowing  this  rest,  it  will  completely  subside  in  the  vessel.  At  the 
end  of  this  time  the  solution  must  be  filtered  to  remove  any  foreign 
substance,  together  with  the  silver  chloride.  The  filtrate  will  then  be 
seen  to  be  a  rich  straw-yellow,  and  the  gold  it  contains  is  ready  for 
precipitation. 

Precipitating  the  Gold. — The  solution  is  now  best  contained  in  a 
large  glass  flask,  and  the  precipitating  reagent  added.  As  gold  is  one 
of  those  metals  which,  as  a  base,  combines  with  very  feeble  affinities, 
it  is  consequently  not  only  very  easily  separated,  but  the  physical  con- 
ditions of  the  precipitate  may  be  much  modified  and  controlled  by 
the  nature  of  the  precipitant,  as  also  by  the  mode  of  operating.  Thus 
gold  may  be  thrown  down  in  a  powder,  in  scales,  in  more  or  less  of  a 
crystalline  state,  in  a  tolerably  compact  sheet  or  foil,  or,  lastly,  in  a 


GOLD.  117 

spongy  condition,  mucli  rosonibling  so-called  "solila"  or  "moss  (ihre." 
And  these  states  may  be  attained  with  some  degree  of  certainty, 
although  the  circumstances  determining  the  more  compact  forms 
are  more  difficult. 

Spontaneous  precipitation  may  take  place  to  some  extent  in  a  vessel 
of  trichloride  of  gold  when  exposed  to  the  air;  and  thus  the  sides  of  the 
vessel  containing  it  will  slowly  become  covered  with  the  deposit.  This 
is  probably  due  to  the  action  of  the  nitrogen  of  the  air.  Many  element- 
ary substances  will  precipitate  gold  from  the  trichloride.  Most  of  the 
lower  metals  reduce  it,  some  metallic  salts  throw  it  down,  and  many 
organic  bodies  readily  precipitate  it.  Thus  sugar  when  boiled  in  it 
gives  at  first  a  light-red  precipitate,  which  afterward  darkens  in  color. 

Practically,  how^ever,  ferrous  sulphate  or  oxalic  acid  are  the  only  precip- 
itants  used.     The  oxalic  acid  is  preferred,  and  is  an  excellent  precipitant. 

The  gold  salt,  being  in  solution,  is  broken  up  by  the  addition  of  a 
strong  solution  of  oxalic  acid,  and  the  gold  is  precipitated  to  the  bottom 
as  either  a  crystalline  mass  or  a  leafy  foil.  It  is  necessary  to  add  a 
slight  excess,  and  the  whole  should  be  kept  at  a  gentle  heat  in  a  sand 
bath  over  a  flame.  Soon  after  the  application  of  heat  some  slight  bub- 
bling is  noticed,  a  copious  evolution  of  gas  takes  place,  and  at  the  same 
time  the  body  of  the  liquid  appears  filled  with  most  delicate  spangles 
of  metallic  gold,  which  become  coherent  as  they  descend,  and  in  con- 
sequence assume  most  any  one  of  the  forms  above  mentioned.  The 
gas  seen  to  escape  is  COj,  from  the  compound,  oxalic  acid.  The 
reaction  is  of  the  simplest — an  acid  on  a  binary  salt — 

2AuC]3  +  3C2H2O4  =  6HC1  +  6CO2  -\-  2Au. 

The  action  of  this  pecipitant  is  gradual,  and  capable  of  much 
regulation,  by  the  amount  and  nature  of  heat  employed,  while  it  is 
also  peculiar  in  being  attended  throughout  by  this  evolution  of  gas 
which  rises  quickly  through  the  solution,  there  is  produced  from  the 
former  cause  a  tendency  in  the  metal  to  deposit  in  a  crystalline  or  crys- 
tallogranular  state;  while  from  the  latter  a  more  or  less  spongy  char- 
acter is  given  to  it;  hence  it  will  be  readily  seen  that  inasmuch  as  we 
are  able  to  modify  these  conditions,  so  we  can  in  the  same  degree  influ- 
ence the  molecular  nature  of  the  result. 

Where  ferrous  sulphate  is  used  about  four  times  the  w^eight  of  the 
gold  will  be  necessary  for  precipitation.  This  may  be  dissolved  quickly 
in  hot  distilled  water  and  added  to  the  gold  solution.  The  precipitate 
thrown  down  is  of  a  brown  color,  and  will,  on  being  gently  burnished 
with  the  finger-nail,  assume  that  metaUic  golden  lustre  characteristic 
of  the  metal.    The  following  is  the  reaction — 

2AUCI3  +  6FeS0^  =  Fe^Clg  +  2Ye^{S0^)i  +  2Au. 

After  the  solution  has  fully  subsided  from  the  disturbance  caused  by 
addition  and  precipitation  a  quantity  of  hot  hydrochloric  acid  may  be 
added,  and  much  of  the  supernatant  liquor  removed,  either  with  a 
siphon  or  by  decantation,  and  the  remainder  of  the  solution  and  pre- 


118     METALS  AND  ALLOYS   USED   /.V  PROSTIIKTIC  DES'lUSTRY. 

cipitate  poured  ujxmi  the  filter  pajxr.  The  precipitate  is  afterward 
washed  with  hvch-ochloric  aeid,  (Ustillcd  water,  a(|ua  aiiiinonia,  and 
a<:jain  witli  (hstilled  water.  The  necessity  of  this  is  apparent,  es{)eeially 
in  the  use  of  ferrous  sulphate,  as  the  precipitate  will  become  more  or 
less  contaminated  with  the  iron.  In  the  use  of  oxalic  acid  this  is  to 
remove  the  cojij)er,  as  goV\  precipitated  hy  oxalic  acid  from  an  acid 
solution  containing  copj)er  is  always  contaminated  with  cupric  oxalate. 
It  is  then  also  advisable  to  heat  the  solution  with  a  slight  addition  of 
potassium  carbonate,  a  soluble  double  oxalate  of  copper  and  potas- 
sium is  formed,  and  the  gold  is  left  in  the  pure  state,  (iold  may  also 
be  precipitated  from  its  acid  solution  in  a  state  of  purity  in  the  form 
of  brilliant  spangles  by  means  of  hydrogen  dioxide,  thus — 

2AUCI3  +  SHjO,  =  6HC1  +  60  +  2Au. 

When  the  precipitated  gold  has  been  carefully  washed  and  rewashed 
with  distilled  water  and  the  above-mentioned  reagents,  it  may  be  dried 
and  placed  in  a  new  crucible,  previously  boraxed,  with  some  potassium 
carbonate  and  potassium  nitrate,  melted,  and  cast  into  an  ingot.  If 
iron  ingot  molds  are  used  the  gold  should  be  washed  after  molding  in 
hot  hydrochloric  acid  to  remove  any  trace  of  metallic  or  oxide  of  iron 
that  may  by  chance  have  adhered  to  its  surface  during  the  process  of 
casting  the  ingot. 

Properties. — Pure  gold  is  of  a  rich,  beautiful,  yellow  color,  of  strong 
metallic  lustre,  unalterable  in  air.  It  is  the  most  ductile  of  all  metals, 
but  ranks  onlv  fifth  in  point  of  tenacity.  One  grain,  however,  if  covered 
with  a  more  tenacious  metal,  like  silver,  forming  a  composite  wire,  may 
be  drawn  into  a  wire  550  feet  in  length,  and  only  ^-gVo"  o^  ^^i  inch 
in  diameter.  It  is  also  the  most  malleable  of  all  metals.  One  grain  of 
it  may  be  beaten  into  leaves  so  thin  as  to  cover  an  area  of  75  square 
inches,  being  of  but  ^ttoito  ^^  ^"  ^^^"^  ^"  thickness. 

Very  thin  leaves  of  gold  appear  green  in  color  by  transmitted  light; 
but  when  heated,  the  light  transmitted  is  ruby-red. 

Gold  possesses  the  property  of  welding  cold.  Thus,  thin  leaves, 
foil,  and  other  forms  of  gold  are  more  especially  adapted  to  the  use  of 
the  dentist  as  a  filling  material.  The  small  particles  are  welded  together 
in  one  perfectly  homogeneous  mass  as  the  filling  is  inserted.  The  finely 
divided  metal,  such  as  that  thrown  down  in  the  preparation  of  pure  gold 
from  the  chloride  solution,  may  be  compressed  between  dies  in  the  form 
of  disks  or  medals. 

The  pure  metal  fuses  at  1100°  C.  or  2012°  F.,  and  its  alloys  at  much 
lower  temperatures.  When  heated  much  abo\e  its  melting  point  it 
slowly  volatilizes  and  is  readily  dissipated  in  vapor  by  the  oxyhydrogen 
flame. 

Pure  gold  is  nearly  as  soft  as  lead,  in  consequence  of  which  articles 
of  jewelry,  coin,  etc.,  made  from  it  are  alloyed  with  copper,  silver, 
platinum,  etc.,  to  give  them  the  recpiisite  hardness,  durability,  and 
elasticity. 

The  specific  gravity  of  gold  cast  in  an  ingot  is  19.2G5;  when  stamped, 
19.31;  and  that  of  the  precipitated  metal  from  19.55  to  19.72. 


OOLD.  119 

Graham  has  shown  that  gold  is  capal)le  of  occhidino;  0.48  of  its  voliimc 
of  hy(h'oi2;cMi,  and  0.2  of  its  vohime  of  nitrogen. 

Alloys.. — (lold  very  readily  unites  witli  most  of  the  metals,  form- 
ing alloys  of  varied  qualities.  When  in  the  pure  state  gold  is  too  soft 
for  any  great  use  other  than  for  filling  teeth;  consecjuently  the  greater 
(juantity  of  gold  is  alloyed  with  some  metal  that  will  increase  its  hard- 
ness and  durability,  without  greatly  impairing  its  more  vahiahle  cjuali- 
ties.  The  metals  usually  employed  for  this  purpose  are  silver,  platinum, 
and  copper. 

Silver  and  gold  are  easily  mixed  together,  but  do  not  seem  to  form 
definite  compounds.  Such  alloys  are  more  fusible,  more  ductile,  harder, 
more  sonorous  and  elastic  than  gold,  and  are  generally  of  a  greenish- 
white  color.  One-twentieth  of  silver  is  sufficient  to  modify  the  color 
of  gold.  The  alloys  of  gold  and  silver  are  known  to  jewelers  as  yellow, 
green,  and  pale  gold,  according  to  the  content  of  silver. 

Copper  and  gold  imite  much  more  readily  than  silver  and  gold ;  indeed, 
it  is  reasonable  to  believe  from  their  behavior  that  a  chemical  com- 
bination is  formed  wdth  76  per  cent,  of  gold  and  24  per  cent,  of  copper. 
Alloys  of  copper  and  gold  are  much  harder,  tougher,  and  more  easily 
fused;  less  malleable  and  ductile,  and  greatly  changed  in  color,  being 
of  a  decidedly  reddish  tint,  depending  upon  the  proportion  of  copper 
with  which  the  gold  is  debased.  An  alloy  of  gold  76,  and  copper  24,  as 
referred  to  above,  is  distinctly  crystalline  and  quite  brittle;  but  a  larger 
proportion  of  either  gold  or  copper  restores  the  malleability  of  the  alloy. 

Standard  Gold. — The  standard  alloy  of  most  nations  is  one  of  copper 
and  gold.  Some  contain  small  quantities  of  silver,  but  this  is  due  to 
imperfect  parting  of  silver  and  gold,  or  it  may  be  contained  in  the  copper 
used  for  the  alloy.  The  proportion  of  copper  to  gold  varies  slightly  in 
different  countries,  and  such  proportions  are  stated  in  thousandths; 
thus,  pure  gold  is  one  thousand  (1000)  fine.  The  following  table  gives 
the  composition  of  standard  gold,  as  fixed  by  the  nations  mentioned : 

Nation.  Gold.  Copper. 

United  States  . 
France    .... 
Germany 
Belgium 

Italy       .... 
Switzerland 

Spain      .... 
Greece     .  .  .  . 

China      .... 
Austrian  Crowns 
Great  Britain  . 
Ducats,  Hungarian  . 
Ducats,  Austrian 
Ducats,  Dutch     . 

The  first  United  States  gold  coins  were  ten-dollar  pieces,  coined  in 
1795;  they  weighed  270  grains  each,  and  were  of  916.666  (22-carat) 
fineness.  Their  weight  was  reduced  in  1S34  to  258  grains,  with  899.225 
(21.581-carat)  fineness;  and  in  1837  the  present  standard  of  900  (21.599- 
carat)  fineness  was  established. 


900  100 

(Carat  21.6—) 


916 

84 

989 

11 

986 

14 

982 

IS 

120     METALS  AM)  ALLOYS    I'Shl)   L\   PROSTHETIC  DENTISTRY. 


Alloys  of  golfl  with  copper,  or  with  silver,  or  with  hoth,  are  much 
used  in  the  manufacture  of  jewelry.  When  the  gold  contains  copjxr 
only  it  is  termed  red  gold;  when,  silver  only,  white  gold ;  if  the  gold  con- 
tains both  metals,  the  caratation  is  termed  mixed.  In  many  countries 
a  legal  standard  of  fineness  is  fixed  for  gold  ornaments  and  jewelry. 
In  England  gold  is  stamped,  or  Hall  Marked,  10,  IS,  and  22-carat;  in 
France,  18,  20,  and  22-carat;  in  Germany,  8,  14,  and  18-carat,  and, 
also,  under  the  term  joujou  gold,  a  G-carat  gold  used  for  electroplated 
jewelry.  The  purpose  of  the  stamping  is  to  protect  the  purc-haser,  who 
is  enabled  to  know  the  carat  of  the  gold  he  is  buying. 

The  following  alloys  used  by  jewelers  are  also  of  much  interest  to 
the   dentist : 

Table  of  Mixed  Caratatiox. — Brannt. 

Parts. 
Carats. 

23 
22 
20 
18 
15 
13 
12 
10 
9 


Gold. 

.Silver. 

Copper. 

23 

1 

h 

22 

1 

1 

20 

2 

2 

18 

3 

3 

15 

3 

6 

13 

3 

8 

12 

3h 

8J 

10 

4 

10 

9 

4J 

10* 

8 

5i 

m 

7 

8 

9 

Colored 

Golds. - 

-Brannt. 

Parts. 

Color. 

Gold. 

Silver. 

Copper. 

Steel.     Cadmium. 

2  to  6 

1.0 

Green. 

75.0 

16.6 

8.4 

(( 

74.6. 

11.4 

9.7 

4.3 

(( 

75.0 

12.5 

12.5 

« 

1.0 

2.0 

Pale  yellow. 

4.0 

3.0 

1.0 

Dark       " 

14.7 

7.0 

6.0 

a               tt 

3.0 

1.0 

1.0 

Pale  red. 

10.0 

1.0 

4.0 

"      " 

1.0 

1.0 

Dark  red. 

30.0 

3.0 

2. 

D 

Grav. 

1  to  3 

1. 

3 

Blue. 

Higher  Carat  Colorei 

J  Gold.s. 

Parts. 

Color. 

Carat. 

Gold. 

Silver. 

Copper. 

15  dwt.       . 

2d 

wt.  18  grs. 

2  dwt.  6 

grs 

Yellow  tint. 

18  K. 

15     " 

1 

"     18    " 

3     "     6 

" 

Red 

" 

18  K. 

1  oz.  16  dwt. 

6 

11 

12     " 

Reddish 

spring  gold. 

16  K. 

1    " 

7 

11 

5     " 

Yellow  tint 

16  K. 

1    " 

2 

" 

8     " 

Re 

d 

" 

16  K. 

Jewelers  usually  make  their  solders  from  the  gold  upon  which  they 
are  to  be  used  by  the  addition  of  small  cjuantities  of  copper,  silver,  oi 


GOLD. 


121 


brass,   the  latter  greatly   increasing  the   fusibility   and   fluidity.     The 
following  are  examples: 

Jewelers'  Soldeks. 


For  18-carat  gold. 

For  16-carat  gold. 

18-carat  gold 

1  dwt. 

16-carat  gold       .          .       1  dwt 

Silver 

2grs, 

Silver         .          .          .10  grs. 

Copper 

Igr. 

Copper       .          .         .       8    " 

Carat. — The  fineness  of  gold  is  also  expressed  in  carats,  a  twenty- 
fourth  part,  formerly  the  twenty-fourth  part  in  weight  of  a  gold  marc. 
It  is  now  assumed  that  there  are  24  carats  in  unity;  whether  the  unit 
be  one  pound,  one  ounce,  or  one  pennyweight,  it  is  divisible  into  24 
equal  parts,  and  each  of  these  parts  is  called  a  carat  to  express  fineness. 
If  a  quantity  of  gold  is  chemically  pure,  in  other  words  contains  no 
alloying  elements,  it  is,  as  we  have  previously  explained,  1000  fine; 
or  as  each  -^  part  is  gold,  it  is  said  to  be  of  24-carat  fineness.  If. 
however,  2  carats,  or  -^  of  the  imit  quantity  are  composed  of  one 
or  more  alloying  metals,  the  gold  is  said  to  be  22  carats  fine;  or  if  6 
carats  or  2^^  of  the  alloy  is  debasing  metal,  the  carat  is  18  fine, 
etc.  The  following  table  shows  the  equivalent  of  each  carat  in  thou- 
sandths : 


Carats. 

1 

2 

3 

4 

5 

6 

7 

8 

9 
10 
11 
12 


Thousandths. 

Carats 

41.667 

13 

83.334 

14 

125.001 

15 

166.667 

16 

208.333 

17 

250.000 

18 

291.666 

19 

333.333 

20 

374.999 

21 

416.667 

22 

458.630 

23 

500.000 

24 

Thousandths. 
541.667 
583.333 
624.555 
666.667 
707.333 
750.000 
791.666 
833.333 
874.999 
916.666 
958.333 
1000.000 


Gold  Plate. — Pure  gold  is  rarely  employed  in  the  dental  laboratory, 
except  for  soldering  continuous-gum  cases,  and  in  some  branches  of 
crown  and  bridge-work.  Its  extreme  softness  and  flexibility  make 
alloying  absolutely  necessary.  The  latter  must  be  accomplished,  how- 
ever, without  practically  impairing  either  its  malleability,  or  pliancy, 
and  at  the  same  time  endow  it  with  that  degree  of  hardness, 
elasticity  and  strength  necessary  to  resist  the  stress  and  wear  to  which 
an  artificial  denture  is  exposed  in  the  mouth. 

Copper  and  silver  are  much  used  to  debase  or  alloy  pure  gold.  It 
is  questionable,  however,  whether  copper  should  be  used  as  almost 
universally  as  it  is;  indeed,  some  regard  it  as  exceedingly  objectionable. 
A  plate  made  from  a  gold  alloy  containing  a  large  percentage  of  copper 
is  more  easily  tarnished,  and  has  a  disagreeable  metallic  taste. 

Silver  exercises  a  very  benign  influence  over  copper  contained  in 
gold  plate,  controlling  the  tendency  to  the  disagreeable  redness.  Equal 
parts  of  silver  and  copper  have  little  or  no  effect  upon  thig  color  of  gold. 


122     METALS  AXn  ALLOYS    VSF.D    IS   PROSTHETIC  DEXTISTRY. 

Silver  assists  in  iinjnirtiiig  Iiurdiiess,  elasticity,  and  durability  to  the 
alloy,  without  so  far  debasing  it  as  copper  alone. 

Platinum  and  silver  are  sometimes  used  to  endow  pure  jujoid  with  the 
qualities  necessary  for  a  dental  base;  but  the  labor  of  swaging  is  very 
greatly  increased  when  platiinmi  is  contained  in  the  ])late. 

In  order  to  secure  the  best  results,  alloys  intended  for  plate  should 
not  be  less  than  18-oarat  in  fineness,  and  the  alloy  should  contain  as  little 
copper   as    possible. 

The  following  are  some  of  the  formnhe  in  use  for  the  preparation  of 
allovs  for  dental  bases: 


Number 

Carat. 

Parts 

(if 
Formula. 

Gold. 

Silver. 

Copper. 

riatinum. 

1' 

18 

18  dwts. 

2  dwts. 

4  dwts. 

2 

18 

18     " 

3     " 

3     " 

3 

18 

18     " 

4     " 

1  dwt. 

1  dwt. 

41 

19 

19     " 

2     " 

3  dwts. 

5 

19 

19     " 

3     " 

1  dwt. 

1     " 

6' 

20 

20     " 

2     " 

2  dwts. 

7' 

21 

21     '• 

1  dwt. 

2     " 

8' 

22 

22     " 

18  grs. 

1  dwt. 

6  grs. 

9^ 

18 

Ml  dwts.  ($60). 

13  dwts. 

10' 

18 

20       " 

2  dwts. 

2  dwts. 

IP 

18 

510  grs.  ($20). 

96.45  grs.  (25c.  coin). 

12' 

19 

20  dwts. 

40  +  grs. 

25  grs. 

13' 

20 

20     " 

20  +    " 

IS     " 

143 

20 

516  srs.  ($20) 

10c.  coiii. 

15' 

21 

20  dwts. 

13  +  grs. 

16' 

21 

20     " 

6    " 

7?  grs. 

Clasp  Gold. — Gold  for  clasps,  elastic  wires,  backings,  stays,  posts, 
pivots,  etc.,  usually  contain  a  small  amount  of  platinum  to  give  it 
greater  strength  and  elasticity.  The  following  formnlcTe  are  recom- 
mended by.  Professor  Chapin  A.  Harris: 

No.  1— 20-Carat.  No.  2— 20-Carat. 

Pure  gold  20  dwts.  Coin  gold            .                20  dwts. 

"     copper       .           .        2     "  Pure  copper       .  .        8  grs 

"    silver         .          .        1  dwt.  "    silver          .  .      10    " 

"    Platinum            .        1     "  "    platinum  .  .      20    " 

A  content  of  ))latinum  in  gold  renders  the  alloy  more  liable  to  oxida- 
tion, and,  says  Professor  Harris,  "This  effect  is  so  marked  that  such 
an  alloy  is  readily  acted  upon  by  nitric  acid."  It  is  not  probable,  how- 
ever, that  the  small  amoimt  contained  in  clasp  gold  would  affect  its 
integrity. 

Crown  Gold. — Gold  for  crowns  should  combine  strength  with  good 
color.  Those  alloys  of  a  large  copper  content  make  exceedingly  un- 
sightly crowns  on  account  of  their  deep-red  color.  Professor  C.  L. 
Goddard  recommends  the  following  for  alloys  the  color  of  pure  gold: 

No.l— 21.6-Carat.  No.  2— 21.6-Carat. 

Pure  gold   .                90  parts.  Coin  gold   .               '      .      50  parts. 

"     silver                   5      "  Pure    "...      45      " 

"     copper          .        5      "  "     silver                      .        5      " 

'  Richardson's  Mechanical  Dentistry,  p.  56. 

2  Johnson  Bros. 

*  Professor  C.  L.  Goddard. 


GOLD.  123 

Gold  Solders. — These  are  usually  alloys  of  gold,  silver,  eop))er,  and 
zinc,  and  are  designed  to  be  a  trifle  more  fusible  than  the  pai-ts  to  be 
soldered;  this  property  is  conferred  upon  them  princij)ally  by  the  con- 
tent of  zinc  (or  brass).  They  should  also  possess  considerable  strength; 
too  much  base  metal,  therefore,  should  not  be  added,  as  it  will,  by 
oxidizing,  tend  to  very  materially  weaken  the  alloys.  Their  carat 
should  be  as  high  or  nearly  as  high  as  that  of  the  plate,  and  their 
color  as  nearly  as  possible  the  same. 

The  following  formuhie  have  yielded  satisfactory  results  as  gold 
solders : 

Parts. 

No.  Carat.     , ^ 

U.  S.  Coin.             Pure  Pure  Pure  Pure  Spelter 

Gold.                   Gold.  Silver.  Copper.  Zinc.       Bras.s.       Solder.* 

1       14  SIO.  4  dwts.  2  dwts. 

2   14     16  dwts 5  "       {iig;;  } 

3  15  6     "  30  grs.  20    "  10  grs. 

4  16  ....  11  dwts.  {3  dwts.}         I   2  dwts.} 

5  16+  ....  {}1^;;.      }  3  dwts.  {,\%\-}      12  grs. 

6  IS  30  parts.  4  parts  1  part.  ....         1  part. 

7  18  ....  27  parts.  4     "  4  parts.  ....         1     " 

8  20  110.  20.64  grs. 

9  20               5  dwts.  12  grs.  6  grs.  6 

(  (18  K.  gold  plate  for-) 
10       14        <^  mulaNo.  9.)  20dwts.  [-  2.5  dwts.  20  grs.  35  grs. 

(        Johnson  Bros.        J 

A  simple  method  for  making  a  good  solder  suitable  for  the  plate  upon 
which  it  is  to  be  used  is :  5  parts  of  the  plate  and  1  of  brass  or  of  silver 
solder.  In  the  case  of  coin  gold,  or  the  crown  alloy  given  above,  a 
solder  thus  made  will  be  exactly  IS  carat.^ 

Rules  for  Computing  and  Compounding  Gold  Alloys^  and 

Examples.^ 

PART    I. 

To  ascertain  the  carat  of  any  given  alloy,  the  proportion  may  be 
expressed  as  follows: 

As  the  weight  of  the  alloyed  mass  is  to  the  weight  of  gold  it  contains,  so  is  24  to 
the  standard  sought. 

Example. — Gold  6  parts,  silver  2  parts,  copper  1  part,  total  9  parts. 

9:6::24:? 
6 
9)144 

16  Answer. 

x^nother  method  when  alloyed  gold  is  used  in  forming  the  mass, 
instead  of  pure  gold,  is  to  express  the  proportion  as  follows — 

As  the  weight  of  the  alloyed  mass  is  to  the  weight  of  the  gold  alloy  used  in  its 
composition,  so  is  the  carat  of  the  latter  to  the  carat  of  the  former — 

1  Composed  of  equal  parts  copper  and  zinc. 
-  Professor  C.  L.  Goddard. 

*  Rules  by  Professor  George  Watt. 

*  Examples  by  Professor  C.  L.  Goddard. 


124     METALS  AM)  ALLOYS    USED  IN  PROSTHETIC  DENTISTRY. 

Example. — Harris  No.  1  solder: 

22-carat  gold  .......  48  parts. 

Copper   .  .  .  .  .  16      " 

Silver 12      " 

Total 76      " 

76 :  48 : :  22  :  carat.  Ans.  13.9  carat. 

PART   II. 

To  reduce  pure  gold  to  any  required  carat,  the  proportion  may  be 
expressed  as  follows: 

As  the  required  carat  is  to  24,  so  is  the  weight  of  gold  used  to  the  weight  of  the 
alloyed  mass  when  reduced.  The  weight  of  gold  subtracted  from  this  gives  the 
quantity  of  alloy  to  be  added. 

Example. — Reduce  6  ouncesof  pure  gold  to  16-carat,  16:24::6  ounces:  9ounces. 
9  —  6  =  3  ounces  alloy  to  be  added. 

To  reduce  gold  from  a  higher  carat  to  a  lower  carat,  the  proportion 
may  be  expressed  as  follow^s: 

As  the  required  carat  is  to  the  carat  used,  so  is  the  weight  of  the  mass  used  to  the 
weight  of  the  alloyed  mass  when  reduced. 

The  weight  of  the  mass  used,  subtracted  from  this,  gives  the  quantity  of  alloy 
to  be  added. 

Example. — Reduce  4  ounces  of  20-carat-gold  to  16  carat: 

16:20::4  ounces:? 

16)80 

5  ounces 
5  ounces  —  4  ounces  =  1  ounce  alloy  to  be  added. 

PART  III. 

To  change  gold  from  a  lower  to  a  higher  carat,  add  pure  gold  or  a 
finer  alloy. 

As  the  alloy  in  the  required  carat  is  to  the  alloy  in  the  given  carat,  so  is  the 
weight  of  the  alloyed  gold  used  to  the  weight  of  the  changed  alloy  required. 

The  weight  of  the  alloyed  gold  used  siibtracted  from  this  gives  the  amount  of 
pure  gold  to  be  added. 

Example. — Change  1  pennyweight  of   16-carat  gold  to  IS-carat.     First  subtract 
16  and  18  from  24  to  find  the  amount  of  alloy  in  each  carat. 
24         24 

6  8  ::  1  pennyweight:? 

J 

6)8^ 

IJ  pennyweights. 
IJ  —  1  ^  §  pennyweight  of  pure  gold  to  be  added. 

To  change  gold  from  a  lower  carat  to  a  higher  carat,  by  adding  gold 
of  a  still  higher  carat. 

Substract  the  lower  carat  and  the  required  carat  each  from  the  highest  carat 
(instead  of  from  24)  and  proceed  as  before. 


GOLD.  125 

Example. — Change  2  pennyweights  of  16-carat  gold  to  IS  carat,  by  adding 
22-carat  gold. 

First  subtract  16  and  IS  from  22. 
22         22 
IS         16 
4  6:2  pennyweights  :  3  pennyweights. 

3  —  2  =  1  pennyweight  of  22-carat  gold  to  be  added. 

Tests  for  Gold  in  Solution. — Sulphuretted  hydrogen  or  ammo- 
nium hydrosulphide  throws  down  a  brown  precipitate  of  auric  sul- 
phide (AujSg).  The  second  precipitant  is  not  used,  however,  as  the 
precipitate  is  soluble  in  it,  as  it  is  also  in  the  alkaline  sulphides.  Auric 
sulphide  is  insoluble  in  nitric  or  hydrochloric  acid  taken  separately, 
but  soluble  in  aqua  regia. 

Ferrous  sulphate  and  oxalic  acid  precipitate  the  gold  in  the  metallic 
state;  it  is  a  browTi  powder,  darker  in  the  instance  of  the  former  than 
the  latter,  but  develops  the  color  and  lustre  of  gold  by  being  burnished 
with  the  finger-nail  or  instrument. 

Stannous  and  stannic  chloride  give  probably  the  most  delicate  test 
for  gold  by  the  formation  of  the  purple  of  Cassius. 

If" the  precipitate  formed  in  the  experiment  above  be  dried  and  heated 
on  charcoal  a  metallic  globule  results. 

Gold  is  reduced  from  many  of  its  compounds  by  sunlight,  and  from 
all  of  them  by  more  or  less  heat. 

Electrodeposition  of  Gold.  By  Simple  Immersion.— From  an  acid 
solution  of  gold  chloride,  the  base  metals,  and  silver,  platinum,  and 
palladium  deposit  gold  in  the  metallic  state.  In  the  double  cyanide  of 
gold  and  potassium  zinc  will  quickly  become  gilded;  copper,  brass,  and 
German  silver,  slowly,  and  antimony,  bismuth,  tin,  lead,  iron,  nickel, 
silver,  gold,  and  platinum  not  at  all. 

Deposition  by  a  Separate  Current.  The  Solution. — There  are  many 
solutions  prepared  for  electro-gilding,  some  being  formed  by  chemical 
means,  others  by  a  separate  current  from  the  battery;  but  whether 
they  are  made  by  chemical  or  electric  process,  the  best  for  a  thick 
reguline  deposit  is  the  pure  double  cyanide  of  gold  and  potassium. 

A  cyanide  solution  may  be  prepared  as  follows: 

Dissolve  120  grains  of  pure  gold  in  one  ounce  of  chemically  pure 
aqua  regia,  thus  preparing  the  chloride  of  gold  as  described  pre- 
viously.^ Dissolve  the  chloride  obtained  in  32  ounces  of  warm  dis- 
tilled water  and  add  to  it  1^-  ounces  of  magnesia;  the  gold  is  precipi- 
tated. Filter  and  wash  with  pure  distilled  water;  digest  the  precipitate 
in  10  parts  of  distilled  water  mixed  with  0.75  part  of  nitric  acid  to 
remove  magnesia;  then  wash  the  remaining  oxide  of  gold  with  distilled 
"water  until  the  wash  water  exhibits  no  acid  reaction  with  test  paper. 
Next  dissolve  3  ounces  of  ferrocyanide  of  potassium  and  6  drachms  of 
caustic  potash  in  34  ounces  of  distilled  water,  add  the  oxide  of  gold 
prepared,  and  boil  the  solution  about  twenty  minutes.  When  the  gold 
is  dissolved  there  remains  a  small  amount  of  iron  precipitated,  which 

1  Preparation  of  Chemically  Pure  Gold. 


126     MFTALS  AND  ALLOYS   USED   L\  PROSTHETIC  DESTIsritV. 

may  be  removed  by  filtering  the  .solution.  The  lifjuid,  a  fine,  elear, 
golden  eolor,  is  then  ready  for  use,  to  be  employed  either  hot  or  cold, 
but  a  better  and  quicker  deposit  is  nearly  always  obtained  from  the 
warm  solution. 

In  electroplating  objects  the  first  essential  is  a  finished  surface,  which 
must  be  made  just  as  it  is  desired  to  be  when  completed.  The  next  is 
cleanliness.  If  it  be  a  silver  denture  or  any  other  metallic  object  it 
should  first  be  cleaned  of  all  surface  combinations,  as  oxides,  sulphides, 
etc.,  by  polishing  in  the  ordinary  way;  then  scrubbed  with  a  solution 
of  hot  water  and  soap  by  means  of  a  brass  or  steel  scratch  brush  on 
the  lathe;  then  washed  or  boiled  in  a  strong  solution  of  caustic  potash, 
afterward  washing  in  distilled  water,  and  finally  in  an  acidulated  water 
to  remove  all  traces  of  the  alkali. 

The  apparatus  is  exceedingly  simple,  consisting  of  a  single  battery 
cell  and  a  glass  bowl  (preferably  of  perpendicular  sides)  to  contain  the 
solution.  The  latter  may  or  may  not  be  adjusted  in  a  water  bath, 
according  to  whether  the  operator  desires  to  work  his  solution  hot  or 
cold.  Aside  from  these,  connecting  and  guiding  wires,  cathode  and  anode 
hooks,  together  with  an  anode,  a  thermometer,  a  scratch  brush,  etc., 
are  all  that  will  be  needed.  The  article  to  be  plated  is  suspended  by 
a  hook  in  the  solution  from  the  cathode,  while  a  piece  of  pure  gold  is 
hung  from  the  anode  to  keep  up  the  strength  of  the  solution,  the  latter 
electrode  being  easily  determined  by  the  fact  that  gas  is  liberated  there 
by  the  passage  of  the  current  through  the  solution. 

When  a  sufficient  coating  has  been  formed  the  object  is  to  be  removed 
from  the  bath  and  burnished  by  the  scratch  brush  or  agate  biu'uisher 
moistened  with  a  solution  of  warm  water  and  soap,  until  the  surface 
is  finished  as  desired. 

SILVER. 

Argent um.  Symbol,  Ag. 

Atomic  weight,  107.12.  Malleability,  second  rank. 

Melting  point,  1040°  (1904°  F.).  Tenacity,  fourth  rank. 

Dvu'tility,  second  rank.  Specific  gravity,  10.53. 

Conductivity  (heat),  100.  Conductivity  (electricity).  100. 

Occurrence. — Silver  is  widely  diffused  throughout  the  earth's  crust. 
It  is  found  chiefly  in  the  United  States,  iSIexico,  Peru,  and  Chile;  Aus- 
tria, Hungary,  Norway,  and  Australia  also  furnish  considerable  amounts. 

Of  the  varieties  of  silver  ores  the  following  chiefly  are  metallurgically 
important:  (1)  reguline  silver,  (2)  horn  silver,  (3)  silver  glance,  (4) 
silver-copper  glance,  (5)  pyrargyrite,  (6)  stephanite,  and  (7)  polybasite. 
Silver  is  also  frequently  met  with  in  base  metallic  ores,  as  in  lead 
ores  and  many  kinds  of  pyrites. 

Chemically  Pure  Silver. — Small  fpiantities  of  this  may  be  easily 
prepared  in  the  laboratory  by  dissolving  conmiercial  or  coin  silver  in 
pure  dilute  (50  per  cent.)  nitric  acid  contained  in  a  Florence  fla.sk, 
hastening  the  action  by  gentle  heating  over  a  sand  bath.  After  the 
silver  has  been  dissolved,  and  the  solution  somewhat  cooled,  add  an 
equal  bulk  of  distilled  water,  and  filter  into  a  second  flask.     To  the 


SILVER.  127 

filtrate  add  a  saturated  solution   of    sodium    chloride  (common   salt) 
until  no  more  white  precipitate  of  silver  chloride  is  formed — 

AgNOs  +  NaCl  =  AgCl  +  NaNOs. 

The  flask  should  then  be  stopped  and  shaken  for  several  minutes 
when,  on  being  allowed  to  rest,  the  chloride  will  quickly  fall  to  the 
bottom,  leaving  a  clear,  supernatant  liquid  above,  which,  if  copj)er  be 
present,  will  be  colored  a  bluish-green.  If  to  this  clear  supernatant 
liquid  the  salt  solution  be  added,  the  operator  is  enabled  to  determine 
instantly  whether  all  of  the  silver  has  been  thrown  down  as  the  chloride, 
or  not.  If  so,  the  clear  liquid  is  decanted  off  and  the  chloride  washed 
until  the  wash  water  does  not  assume  the  slightest  tinge  of  blue  upon  the 
addition  of  ammonia.  The  chloride  is  now  best  transferred  to  a  beaker, 
or  some  other  wide-mouthed  vessel,  and  about  twice  its  bulk  of  water, 
acidulated  with  about  10  per  cent,  of  sulphuric  acid,  added.  Several 
small  pieces  of  iron  in  some  form,  preferably  lath-nails,  may  now  be 
added  to  the  mixture,  and  the  whole  stirred  with  the  closed  end  of  a  test- 
tube.  The  following  reactions  then  take  place,  during  which  ferrous 
sulphate  and  hydrochloric  acid  are  formed  and  silver  liberated,  thus — 

Fe  +  H2SO4  =  FeSO,  +  H^,  and 
2H  +  2AgCl  =  2HC1  +  2Ag. 

The  completion  of  the  reaction  is  recognized  by  the  changing  of  the 
precipitated  mass  from  white  to  a  dark  gray,  which  is  the  color  of  the 
finely  divided  silver.  The  small  pieces  of  iron  are  now  removed,  the 
precipitated  silver  w^ashed  and  rewashed  with  dilute  hydrochloric  acid, 
then  with  distilled  water,  dried,  mixed  with  about  an  equal  bulk  of 
potassium  carbonate,  and  melted  in  a  well-boraxed  crucible. 

Properties. — Silver  is  the  whitest  of  metals,  very  brilliant,  tenacious, 
malleable,  and  ductile,  in  the  last  two  qualities  being  inferior  only  to 
gold;  if  considered  weight  for  weight,  it  is  superior  to  gold,  for  while  one 
grain  of  gold  may  be  beaten  so  thin  as  to  cover  an  area  of  75  square 
inches,  a  grain  of  silver  may  be  made  to  cover  98  square  inches,  though 
the  foil  of  the  former  is  much  thinner  than  that  of  the  latter.  The  extent 
of  the  malleability  of  gold  and  silver  has  never  been  absolutely  deter- 
mined, as  the  means  employed  have  invariably  failed  before  the  prop- 
erty in  either  was  exhausted.  In  tenacity  silver  is  superior  to  gold. 
It  is  also  harder  than  gold,  but  softer  than  copper,  and  is  the  best-known 
conductor  of  heat  and  electricity.  It  fuses  at  1040°  (1904°  F.),  far 
below  the  fusing  point  of  either  gold  or  copper.  It  volatilizes  appre- 
ciably at  full  red  heat;  in  the  oxyhydrogen  flame  it  boils,  with  the 
formation  of  a  blue  vapor.  The  fused  metal  readily  absorbs  oxygen 
gas  (when  used  under  potassium  nitrate  it  takes  up  as  much  as  twenty 
times  its  volume).  As  the  metal  cools  the  oxygen  escaping  through  the 
semisolid  crust  on  the  surface  of  the  fused  mass  produces  very  beauti- 
ful effects.  Pure  silver  retains  a  trace  of  the  absorbed  oxygen  per- 
manently. It  is  unaltered  in  the  air  at  any  temperature,  but  is  readily 
acted  upon  by  sulphur,  phosphorus,  or  chlorine. 

Nitric  acid  is  the  proper  solvent  for  silver,  and  is  most  efficient  when 
diluted  about  50  per  cent.,  but  active  whether  concentrated  or  dilute. 


128     METALS  AND  ALLOYS   USED   L\  PROSTHETIC  DENTISTRY. 

with  the  profhiction  of  nitric  oxide  (X/)-..)  and  silver  nitrate  (AgXOg). 
Sulphuric  acid,  hot  and  concentrated,  acts  upon  silver,  forming  a  sul- 
phate which  is  sparingly  soluble.  Hydrochloric  acid,  hot  and  concen- 
trated, forms  argentic  chloride.  Fused  alkaline  hydrates  or  nitre  are 
without  action  upon  silver;  hence  it  is  usetl  for  the  manufacture  of 
crucil)lcs  for  the  fusion  of  caustic  alkalis,  etc. 

Alloys. — Pure  silver  is  too  soft  for  coinage  or  comnicrcial  purposes; 
it  is,  therefore,  alloyed  variously  for  its  different  usages  to  increase  its 
hardness. 

Gold. — Formerly  silver  was  much  used  to  alloy  gold.  The  metals 
are  easily  mixed  together,  but  do  not  appear  to  form  definite  c-ompounds. 
With  certain  proportions  of  the  metals  the  resulting  alloys  are  more  duc- 
tile, harder,  more  sonorous  and  elastic  than  either  metal  considered  singly. 

Copper. — The  alloys  of  copper  and  silver  are  the  most  useful  of  the 
alloys  of  silver.  In  most  countries  the  silver  coins  are  made  of  these 
two  metals.  In  the  United  States  the  silver  for  coinage  is  alloyed  with 
10  per  cent,  copper,  the  proportion  of  each  being  stated  in  the  thou- 
sandths; thus,  pure  silver  being  1000  fine,  the  coin  or  "standard  silver" 
is  900  fine,  with  100  parts  copper  added.  The  German  and  French 
silver  coins  are  of  the  same  grade,  those  of  Great  Britain  are  925  fine, 
with  75  parts  of  copper  added,  being  known  as  "sterling"  silver.  Most 
silverware  is  of  "sterling"  fineness.  The  presence  of  copper  does  not 
modify  the  color  of  silver  so  long  as  the  proportion  of  the  former  does 
not  exceed  40  or  50  per  cent.  Copper  imparts  to  silver  greater  hard- 
ness, tenacity,  and  strength. 

Comparison  of  the  silver  dollar  of  the  United  States  with  that  of 
Mexico : 

United  States  Mexican 

dollar.  dollar. 

Pure  silver 371.25  grs.         377.14  grs. 

"    copper 41.2-5    "  40.65    " 


Total  weight       ....     412.50    "  417.79    " 

The  Mexican  dollar  weiglis  0.866  of  a  Troy  ounce. 

Zinc  and  silver  have  a  great  affinity  for  each  other,  and  are  conse- 
quently readily  alloyed. 

Silver  solder  for  soldering  the  metal  is  usually  composed  of  an  alloy 
with  copper  and  zinc.     The  following  are  well  adapted  for  the  porpo.se: 

No.  l.>  No.  2.2 


Silver 

.      66  parts. 

Silver 

6  parts, 

Copper    . 

.      30      " 

Copper 

.     2     " 

Zinc 

.      10      " 

Brass 

1  part. 

"When  the  material  to  be  united  is  composed  of  pure  silver  and  plat- 
inum, silver  coin  alloyed  with  one-tenth  zinc  may  be  used  as  a  solder." 

So-called  "Standard"  silver  is  also  an  excellent  solder  for  high 
fusing  brass  and  German  silver.  If  the  article  is  to  be  soldered  tw^ice, 
this  may  be  used  first  and  the  silver  solder  afterward.' 


'  Richardson'.*  Mechanical  Dentistry,  p.  78. 

"-  Ibid. 

»  Professor  C.  L.  Goddard. 


SILVER.  129 

Dr.  Kirk'  recommends  the  following  compositions: 


Fine  silver. 

Copper 

Brass. 

Zinc. 

4.0 

3.0 

.    2.0 

1.0 

19.0 

V.6 

10.0 

5.6 

66.7 

23.3 

10.0 

50.0 

33.4 

16.6 

11.0 

4.0 

V.o 

These  may  be  used  for  soldering  the  surfaces  of  standard  silver. 

Electrodeposition  of  Silver. — Silver  is  the  most  important  and 
prominent  metal  in  electroplating  processes. 

The  solution  generally  used  is  the  cyanide,  and  it  may  be  prepared 
by  either  of  two  methods — the  battery  or  the  chemical  process. 

The  method  of  procedure  in  the  former  is  simple,  when  thoroughly 
understood.  First,  the  percentage  of  actual  cyanide  in  the  cyanide 
salt  used  must  be  ascertained.  If  it  contains  about  50  per  cent.,  dis- 
solve each  ounce  in  about  one  quart  of  distilled  water;  or  if  it  contains 
more,  add  more  water  and  vice- versa  in  proportion.  Suspend  a  large 
anode  and  a  small  cathode  of  silver  in  the  liquid,  and  pass  a  strong 
current  of  electricity  through  until  the  required  amount  of  metal  is  dis- 
solved from  the  anode.  As  this  process  produces  some  caustic  potash 
in  the  liquid,  some  of  the  strongest  hydrocyanic  acid  may  now  be 
added  to  form  this  into  the  cyanide,  and  more  of  the  anode  dissolved 
in  the  mixture  by  the  battery. 

Solutions  for  deposit  are  made  by  the  chemical  process  as  follows: 

Take  four  parts  of  pure  grain  silver  and  reduce  it  to  argentum 
nitrate  by  mixing  with  nitric  acid.  Dissolve  this  in  distilled  water,  in 
the  proportion  of  one  quart  to  every  one-half  ounce  of  silver  used.  At 
the  same  time  make  a  solution  of  from  two  to  three  parts  of  cyanide  of 
potassium  in  twenty  or  thirty  parts  of  distilled  water.  This  is  to  be 
added  gradually  to  the  solution  of  nitrate  of  silver  as  long  as  it  produces 
a  white  precipitate.  If  too  much  be  added,  however,  it  will  cause  some 
of  the  precipitate  to  be  redissolved  and  wasted.  In  such  a  case  the 
liquid  should  be  stirred  and  then  allowed  to  settle  clear.  A  small 
amount  of  nitrate  of  silver  dissolved  in  distilled  water  should  be  added 
as  long  as  it  produces  a  white  cloud.  This  may  be  better  observed  by 
using  a  separate  glass  vessel  to  see  the  precipitate  as  it  dissolves.  The 
liquid  should  now  be  left  to  settle  until  quite  clear,  and  the  clear  portion 
then  decanted,  and  the  precipitate  washed  four  or  five  times  in  a  large 
quantity  of  water  by  simply  adding  the  water,  stirring,  and  allowing  it 
to  settle  again,  and  decanting  as  before.  Next  dissolve  from  six  to 
eight  parts  of  cyanide  of  potassium  in  twenty  parts  of  distilled  water, 
adding  it  a  portion  at  a  time,  with  free  stirring,  to  the  w^et  cyanide  of 
silver,  until  the  whole  is  barely  dissolved;  then  add  about  three  parts 
more  of  cyanide  of  potassium  to  form  free  cyanide,  and  sufficient  dis- 
tilled water  to  reduce  the  whole  to  the  proportion  of  about  one-quarter 
of  an  ounce  of  silver  to  the  quart;  finally,  when  all  the  free  cyanide  is 

1  American  System  of  Dentistry,  vol.  iii.  p.  S79. 


loO    MKTALS  AND  ALLOYS   USED   IS  riKJSTUKTlf  DENTISTRY. 

dissolved,  filter  the  solution  uiid  it  is  ready  for  use.  The  speeifie  gravity 
of  the  solution  should  be  maintained  at  between  l.S  and  1.15.  Deposit 
solutions  are  very  numerous,  V)ut,  in  the  author's  judgment,  the  above 
is  best  adapted  for  a  good,  reguline  solid  deposit. 

Knowledge  of  the  management  of  solutions  is  essential.  There  are 
varying  cireumstances  which  must  be  noted  in  order  to  keep  them  in 
good  condition  for  a  reguline  deposit.  New  solutions  do  not  work  a> 
well,  usually,  as  old  ones,  provided  the  latter  are  not  too  old.  Solutions 
of  two  or  three  years  of  age  work  probably  the  best.  They  change 
from  many  causes;  they  become  dirty  and  concentrated  from  exposure; 
increase  or  decrease  in  their  relative  proportions  of  cyanide  and  metal; 
they  acquire  other  metals  in  solution,  dissolved  from  the  anode  and 
corroded  from  the  cathode;  plaster  and  plumbago  accumulate  in 
them,  in  consequence  of  which  they  should  be  filtered  ;  they  grad- 
ually decompose,  become  brown,  discolored,  and  evolve  ammonia  by 
exposure  to  light,  especially  if  they  contain  too  much  free  cyanide; 
therefore,  all  these  deviations  from  the  proper  condition  should  be  cor- 
rected. The  specific  gravity  should  be  maintained,  and  the  proper 
amount  of  metal  and  cyanide  kept  in  solution.  To  determine  any  dis- 
proportion in  the  latter,  place  25  grams  of  the  solution  in  a  test-tube 
of  proper  size,  and  add  to  it,  at  first  freely,  and  afterward  gradually, 
at  last,  drop  by  drop,  with  constant  stirring,  a  solution  of  1  gram 
of  crystallized  nitrate  of  silver  in  10  grams  of  distilled  water.  If  the 
precipitate  formed  is  dissolved  rapidly,  with  but  little  need  of  stir- 
ring, there  is  too  much  cyanide.  If,  however,  it  does  not  dissolve,  even 
after  much  stirring,  there  is  too  little  cyanide;  but  if  it  wholly  dissolves 
(the  latter  part  (juite  slowly)  the  proportion  of  silver  to  cyanide  is  about 
correct. 

Many  other  minor  troubles  not  mentioned  are  encountered,  which 
must  be  corrected  by  means  gathered  only  from  experience  in  working 
the  process. 

The  processs  for  making  dental  bases  by  electro-deposition  on  the 
plaster  cast  of  the  mouth  was  patented  February  5,  1889,  by  Joseph 
G.  Ward,  of  Irvington,  X.  J. 

The  author  has  had  some  experience  in  the  work;  in  fact,  was  engaged 
in  perfecting  a  process  for  the  same  result  when  ]Mr.  Ward  secured  his 
patent.  The  method  of  proceedure  in  the  preparation  of  a  dental  base 
is  as  follows: 

A  true  impression  of  the  mouth  is  secured,  and  from  this  a  cast  is 
obtained  by  casting  in  the  usual  manner.  After  the  cast  ha.s  become 
thoroughly  dry  it  should  be  soaked  in  hot  fluid  paraffin,  until  saturated, 
and  before  cooling  the  surface  is  wiped  clean  of  all  superflous  adhesions 
which  might  in  any  way  destroy  the  exactness  of  the  surface.  The  cast 
is  then  coated  freely,  A\here  the  deposit  is  desired  with  a  mixture  of 
ecjual  parts  of  pure,  finely  ])ulverized  plumbago  and  the  finest  tin-bronze 
powder  or  any  other  conducting  substance  which  would  be  suitable 
for  the  purpose.  This  is  applied  with  a  thick,  short-haired  camel's- 
hair  pencil.  The  cast  is  now  so  wired  that  perfect  connection  is  made 
with  the  palatal,  buccal,  and  labial  surfaces.       From  these  guiding 


PLATINUM.  131 

wires  a  cathode  hook  suspends  the  cast  in  the  solution.  After  the 
metal  has  been  deposited  to  a  sufficient  thickness,  the  cast,  with  its 
deposit,  is  to  be  taken  from  the  bath,  the  deposit  removed  from  the 
cast,  trimmed  and  polished;  but  if  it  is  desired  to  have  the  plate  of 
increased  thickness  at  any  part  to  give  the  appearance  of  a  turned 
rim,  etc.,  the  cast,  with  the  deposit  adhering  to  it,  may  be  removed 
from  the  bath,  and  all  the  exposed  surface  of  the  deposit,  except  the 
portions  to  be  thickened,  may  be  covered  with  a  coating  of  wax  or 
some  other  non-conducting  substance,  and  re-submerged  in  the  bath 
and  left  there  until  the  required  thickness  of  deposit  is  secured  in  the 
parts  desired.  It  may  then  be  taken  from  the  bath,  burnished,  trimmed 
by  scraping,  burring,  and  filing  to  the  proper  shape  and  thickness,  then 
polished,  and  spurred.  A  thick  plating  of  gold  should  now  be  added 
to  the  properly  shaped  plate,  or  the  rubber  for  the  attachment  of  the 
teeth  will  not  harden  and  adhere  to  the  plate  during  the  process  of 
vulcanization  (the  sulphur  of  the  vulcanite  combining  with  the  silver). 
After  the  teeth  have  been  attached  and  the  vulcanite  and  all  properly 
finished,  a  second  coating  of  gold  should  be  electroplated  over  it  all  to 
cover  portions  that  had  been  made  bare  in  finishing  the  vulcanite. 

The  denture  may  be  made  by  depositing  the  metal  directly  on  the 
teeth  as  in  cheoplasticwork,  and, where  necessary,  clasps  maybe  formed. 
Broken  dentures  have  been  soldered  with  18-carat  gold  solder. 

Crown  and  bridge  work  may  also  be  made  in  various  ways  by  this 
process. 

PLATINUM. 

Platinum.  Symbol,  Pt. 

Atomic  weight,  193.3  Malleability,  sixth  rank. 

Melting  point,  oxyhj'drogen  flame,  Tenacity,  third  rank. 

1 770°  C.  Specific  gravity,  21.46. 

Ductility,  third  rank.  Conductivity   (electricity),  18.8. 
Conductivity  (heat),  8.4. 

(Silver  being  100.) 

Occurrence. — ^The  ore  of  platinum,  "  polyxene,"  which  is  a  most 
complex  mixture  of  a  number  of  heavy  reguline  species  of  platinum, 
osmiridium,  iron-platinum,  platin-iridium,  iridium,  palladium,  gold, 
and  a  number  of  non-metallic  species,  notably  chrome-iron  ore,  mag- 
netic iron  oxide,  zircone,  corundum,  and  occasionally  also  diamond, 
is  found  in  the  province  of  Choco,  South  America,  wdiere  it  was  first 
discovered  in  1736,  in  New  Granada,  Barbacos,  California,  and  Aus- 
tralia, but  chiefly  in  alluvial  deposits  in  the  Ural  district  in  Russia. 

Fusing-  Platinum. — By  means  of  the  oxygen  blowpipe  the  spongy 
platinum  is  easily  reduced  to  a  compact  mass,  a  result  formerly  only 
fairly  well  obtained  by  the  very  tedious  and  laborious  means  of  welding. 

The  furnace  for  fusing  platinum  (^Fig.  114)  is  at  once  a  cupel  aiid 
furnace,  consisting  of  two  thoroughly  burned  lime  blocks  with  a  Ixisin- 
like  concavity  in  each,  and  fitted  one  over  the  other.  The  concavity 
in  the  lower  block  forms  the  bed  of  the  furnace,  and  is  provided  with  a 
gutter  leading  from  the  basin  to  the  outside.      Through  the  top  are 


132     METALS  AND  ALLOYS   USED  IS  PROSTHETIC  DENTISTRY. 

passed  the  oxyhydrogen  blowpipes.  These  each  consist  of  two  con- 
centric tubes,  a  small  inner  and  a  larger  outer  tube.  Through  the 
outer,  or  larger,  tube  the  hydrogen  or  illuminating- gas  is  passed,  and 
through  the  inner,  or  smaller,  the  oxygen  is  forced  into  the  centre  of 
the  flame.     The  tubes  are  of  copper,  tipped  with  platimnn. 

Platinum  scraps  are  melted  by  first  heating  up  the  furnace  and  then 
introducing  them  through  an  opening  in  the  side.  In  the  case  of  plat- 
inum sponge  the  mass  is  introduced  before  heating  up  the  furnace,  and 
it  is  here  that  the  furnace  acts  as  a  cupel;  the  impurities  remaining  in 
the  metal  are  oxidized  and  volatilized  or  absorbed  by  the  lime  of  the 
furnace.  The  temperature  produced  is  supposed  to  be  about  2870°  C. 
Osmium  does  not  melt  at  this  point,  but  if  present  it  is  volatilized 
with  palladium  and  gold. 


Fig.  114. 


c^;^-^ 


Furnace  for  fusing  platinum. 


Properties. — The  metal  is  bluish  silver-white,  about  as  soft  as  pure 
copper,  and  has  a  specific  gravity  of  21.46.  It  is  tough,  ductile,  and 
malleable,  and  may  be  rolled  or  iSeaten  into  foil  or  drawn  into  wire  of 
almost  microscopic  fineness.  Dr.  Arendt  states  that  a  cylinder  of 
platinum  one  inch  in  diameter  and  five  inches  long  may  be  drawn 
into  a  wire  sufficiently  long  to  encircle  the  earth  at  the  ecjuator.  The 
fine  wire  used  in  the  micrometer  eye-piece  of  microscopes  suggested 
by  Wollaston  is  made  by  drawing  a  composite  wire  of  platimnn  coated 
with  silver  to  its  greatest  attenuation,  and  then  dissolving  off  the  silver 
in  nitric  acid.  Platinum  possesses  tenacity  in  a  high  degree,  being 
slightly  inferior  to  iron  and  copper.  The  fusing  point,  according  to 
Violle,  is  1779°  C.  When  heated  much  above  its  fusing  point,  it  soon 
begins  to  volatilize.  The  fused  metal,  like  silver,  absorbs  oxygen, 
and  consequently  "spits"  on  freezing.  At  a  red  heat  it  "occludes" 
hydrogen  gas.    The  volume  of  hydrogen  absorbed  by  a  unit  volume  of 


PLATINUM.  133 

metal  at  a  red  heat,  under  one  atmosphere's  pressure,  was  found,  in 
the  case  of  the  fused  metal,  to  vary  from  0.13  to  0.21,  volume  measured 
cold;  in  the  case  of  merely  welded  metal  from  2.34  to  3.8  volumes. 
Oxygen,  though  absorbed  by  the  liquid,  is  not  occluded  by  the  solid 
metal  at  any  temperature,  but  when  brought  in  contact  with  it  at 
moderate  temperatures,  suflFers  considerable  condensation  at  its  sur- 
face, and  in  such  a  state  exhibits  a  high  degree  of  chemical  affinity. 
When  a  jet  of  hydrogen  gas  strikes  a  layer  of  spongy  platinum  it  causes 
it  to  glow  and  the  gas  takes  fire. 

The  most  striking  example  of  the  property  of  the  metal  for  absorb- 
ing gases  is  demonstrated  in  the  finely  divided  state  known  as  "plat- 
inum black."  This  state  is  produced  by  dropping  platinum  chloride 
solution  into  a  boiling  mixture  of  3  parts  of  glycerin  and  2  of  caustic 
potash.  Platinum  black  is  said  to  absorb  800  times  its  volume  of 
oxygen  from  the  air,  and  is,  therefore,  a  most  active  oxidizing  agent, 
acting  catalytically — i.  e.,  after  having  given  up  its  oxygen  to  the  oxi- 
dizable  substance  it  takes  up  a  fresh  supply  from  the  atmosphere. 

Platinum  is  not  dissolved  by  any  single  acid,  its  proper  solvent  being 
nitrohydrochloric  acid. 

The  caustic  alkalis,  the  alkaline  earths,  nitrates  and  cyanides,  and 
especially  the  hydrates  of  barium  and  lithium,  attack  platinum  at  a  red 
heat,  although  the  alkaline  carbonates  have  no  effect  at  the  highest 
temperatures.  Sulphur,  in  the  absence  of  alkalis,  has  no  action,  but 
phosphorus  and  arsenic  attack  platinum  when  heated  with  it. 

Direct  contact  of  platinum  with  burning  charcoal  should  be  avoided, 
since  the  silicon  reduced  from  the  charcoal  ash  unites  with  platinum, 
making  it  brittle  and  liable  to  fracture. 

Heating  platinum  with  spirit  lamps  is  preferable  to  the  use  of  ordinary 
gas.  When  gas  is  used,  care  should  be  taken  to  have  the  supply  of  air 
sufficient  to  ensure  complete  combustion,  since,  with  the  flame  con- 
taining free  carbon,  the  platinum  suffers  deterioration  by  the  forma- 
tion of  a  carbide  of  platinum.  For  this  reason,  also,  the  inner  cone  or 
reducing  flame  should  not  come  in  contact  with  the  metal. 

Platinum  was  introduced  in  France  as  early  as  1820  for  a  base  in 
continuous-gum  work.  Its  low  rate  of  expansibility  under  increased 
temperature,  its  coefficient  being  about  equal  to  that  of  glass,  and  its 
very  high  fusing  point  make  it  most  useful  as  a  base  for  porcelain  work, 
and  for  pins  for  artificial  teeth.  Its  comparatively  great  resistance  to 
chemical  agents  ensures  it  against  corrosive  action,  and  places  it  on  an 
equality,  in  this  particular,  with  gold  for  dental  bases,  crowns,  and 
bridge  work. 

Coils  of  platinum  wire  are  useful  in  dental  offices  in  various  forms 
of  electric  heating  devices.  The  heat  is  free  from  products  of  combus- 
tion and  can  be  most  accurately  controlled.  A  device  of  this  nature 
is  especially  valuable  in  annealing  gold. 

Alloys. — Platinum  alloys  with  most  of  the  metals.  With  mercury 
spongy  platinum  unites  to  form  an  exceedingly  unctions  amalgam. 
It  does  not  unite  readily,  and  its  union  is  best  accomplished  by  con- 
tinuous rubbing:  in  a  warm  mortar. 


l.']4     Mh'TALS  AXD   ALLOYS   USED   J.\  rnosTIIKTIC  DF.STLSTRY. 

Iridium  from  10  to  If)  per  cent,  added  to  plntimim  greatly  increases 
its  hardness,  elasticity,  infusihility,  and  resistance  to  chemical  action. 
Platinum  alloyed  with  iridium  can  he  made  very  useful  in  dentistry 
to  strengthen  weak  parts  of  {)artial  continuous-gum,  partial  vulcanite 
dentures,  and  crown  and  bridge  work. 

An  alloy  of  7S.7  platinum  and  21.3  iridium  will  withstand  the  action 
of  acjua  regia.     E(jual  parts  of  the  metals  form  a  very  l)rittle  allov. 

(iold  and  })hitinum  form  an  alloy  of  great  value  for  the  construction 
of  dental  bases.  Platinum  gives  to  gold  a  greater  hardness  and  elas- 
ticity. Two  parts  to  one  of  gold  forms  a  brittle  alloy,  while  with  equal 
parts  the  alloy  is  malleable.  Prinsep  found  that  7  parts  of  g<jld  and  3 
parts  of  platinum  formed  an  alloy  infusible  in  the  strongest  l)tast  furnace. 
Gold  11  parts  and  platinum  1  part  form  a  grayish-white  alloy,  having 
somewhat  the  appearance  of  tarnished  silver. 

Gold  75  parts  and  platinum  25  parts  form  an  alloy  much  used  in 
continuous-gum  and  porcelain  crown  and  bridge  work.  It  is  usually 
called  25  per  cent,  platinum  solder. 

By  small  additions  of  platinum  to  silver  its  pure-white  color  is 
changed  to  a  gray,  and  its  hardness  is  increased.  The  alloys  are 
difficult  to  make,  on  accoimt  of  the  separation  of  the  platinum,  owing 
to  its  greater  specific  gravity. 

Platine  au  titre,  an  alloy  composed  of  from  65  to  S3  per  cent,  of  silver, 
has  been  used  for  dental  bases  in  preference  to  coin  silver,  on  account 
of  its  resistance  to  chemical  action  and  its  greater  elasticity.  Nitric 
acid  will  dissolve  an  alloy  of  silver  and  platinum  when  the  latter  is 
not  present,  to  exceed  10  per  cent. 

Cadmium  and  platinum  unite,  to  form  a  definite  compound,  having 
the  formula  of  PtCdj. 

Copper  and  platimnn,  equal  parts,  form  a  gold-colored  alloy  tarnish- 
ing in  air. 

Lead  and  tin  unite  with  platinum  in  all  proportions,  resulting  in  hard 
and  brittle  alloys  of  low  fusing  points.  Pure  platinum  should,  there- 
fore, never  be  brought  in  contact  with  these  or  other  low  fusing  metals 
or  their  alloys  at  high  temperatures,  as  alloys  with  platinum  having  a 
low  fusing  point  and  brittle  character  are  readily  formed. 


IRIDIUM. 

Iridium.  Symbol,  Ir 

Atomic  weight,  191.5.  Malleable,  at  red  heat. 

Melting  point,  oxyhydrogen  flame.  Specific  gravity,  22.40. 

Conductivity  (heat).  Conductivitv  (electricity). 
Silver  being  100. 

Occurrence. — This  metal  occurs  chiefly  as  a  native  alloy  of  iridium 
and  osmium,  known  as  osmiridium  or  iridosmine.  It  is  also  found 
thus  combined  with  platinum,  and  is  contained  in  gold  from  several 
localities,  especially  that  from  some  mines  of  California  and  in  the 
Frazer  River  district  of  British  Columbia,  causing  much  inconvenience. 

Properties. — Iridium  is  a  steel-white  metal,  exceedingly  hard,  brittle 
when  cold,   but  somewhat  malleable    at   red  heat,  having   a  specific 


MERCURY.  ^'^r) 

gravity  of  22.40,  unaltered  in  air,  and  fusible  only  in  the  oNyliydi'()i;-en 
flame.  If  the  precipitated  metal  he  moistened  with  a  small  (piautity 
of  water,  pressed  tightly  between  filter  paper,  and  then  very  forcibly 
in  a  press,  and  calcined  at  a  white  heat,  it  may  be  obtained  in  the  form 
of  a  very  hard  compact  mass,  capable  of  taking  a  good  polish,  but  still 
very  porous,  and  having  a  specific  gravity  not  exceeding  10. 

The  pure  metal  itself  is  not  acted  upon  by  the  acids,  but  when  reduced 
by  hydrogen  at  a  low  temperature  it  oxidizes  slowly  at  a  red  heat,  and 
may  be  dissolved  in  nitrohydrochloric  acid. 

Alloys. — With  gold  iridium  forms  a  malleable  and  ductile  alloy, 
its  color  depending  upon  the  proportions  of  the  metals. 

Platinum  and  iridium  form  some  very  valuable  and  useful  alloys.^ 
Aside  from  these,  and  the  use  of  the  metal  and  its  alloy  with  phosphorus 
for  pointing  gold  pens,  iridium  is  of  little  value. 

With  silver  it  is  claimed  there  is  no  alloy,  and  that  after  exposing  a 
mixture  of  these  metals  to  a  high  temperature,  or  attempting  to  pour 
out  the  contents  of  the  crucible,  silver  alone  flows  out  and  a  thick  mass 
is  left  in  the  crucible. 

MERCURY. 

Hydrargyrum.  Symbol,  Hg. 

Atomic  weight,  198.5.  Malleable  at  —39°  C. 

Melting  point,  —39°  C.  Ductile  at— 39°  C. 

Boiling  point,  357.3°  C.  Specific  gravity,  13.595. 

Conductivity  (heat),  greater  than  water.     Conductivitj'^  (electricity),  1.49. 

Silver  being  100. 

Occurrence. — ^Mercury  occurs  in  nature  chiefly  as  the  red  sulphide, 
HgS,  cinnabar,  which,  as  a  rule,  is  accompanied  by  more  or  less  of  the 
reguline  metal.  The  most  important  mercury  mines  of  Europe  are 
those  of  Almaden,  Spain,  and  of  Idria,  in  Illyria;  it  is  also  found  in 
China,  Mexico,  Corsica,  Peru,  and  California.  The  European  mines, 
until  lately,  furnished  the  bulk  of  the  mercury  of  commerce,  but  they 
have  been  eclipsed  by  the  rich  deposits  of  New  Almaden,  near  San  Jose, 
California.  The  mines  of  the  latter  have  been  the  most  productive  in 
the  world,  yielding  more  than  3,000,000  pounds  annually,  and  large 
quantities  are  still  taken  from  them.  The  California  cinnabar  is  richer 
in  mercury,  because  purer,  than  the  Spanish,  the  former  yielding  about 
70,  the  latter  about  38  per  cent,  of  mercury. 

Mercury  is  also  found  free,  forming  an  amalgam  with  silver,  and  in 
the  form  of  protochloride  (native  calomel). 

Properties. — Mercury,  or  quicksilver,  as  it  is  often  called,  is  of  a 
silver-white  color,  liquid  at  ordinary  temperature  (above  — 39°  C), 
odorless,  and  tasteless.  Volatile  at  common  temperature,  but  more 
rapidly  volatihzes  as  the  temperature  increases,  and  at  357.3°  C.  it 
boils,  being  finally  volatilized  without  residue,  ^lien  globules  are 
dropped  upon  white  paper  they  should  roll  about  freely,  without  tailing, 
retaining  their  globular  form.  It  should  be  perfectly  dry,  and  present 
a  bright  surface.     When  perfectly  pure  it  undergoes  no  alteration  by 

1  See  Pla,tinum. 


136     METALS  AXD  ALLOYS   USED   IN  PROSTHETIC  DENTISTRY. 

the  action  of  the  air  or  of  water,  hut  in  the  ordinary  state  it  will  exhihit 
a  sliffht  tarnish.  It  solidifies  at  — 39°  C.  with  considerable  contraction 
into  a  compact  mass  of  regular  octahedra,  which  can  be  cut  with  a 
knife  or  flattened  under  the  hammer. 

Action  of  Acids  on  Mercury.— Hydrochloric  acid  does  not  attack 
mercury.  Sulphuric  acid,  boiling,  converts  it  into  mercurous  sulphate, 
liberating  sulphur  dioxide. 

Nitric  acid  is  the  most  effective  solvent  for  mercury.  It  dissolves 
readily  in  the  dilute  acid  if  heated,  or  in  the  cold,  if  nitrous  acid  is 
present;  with  the  strong  acid,  heat  is  soon  generated,  and  with  con- 
siderable quantities  of  the  material  the  action  accjuires  an  explosive 
violence.  At  ordinary  temperatures,  dilute  nitric  acid,  when  applied 
in  slight  excess,  produces  chiefly  normal  mercurous  nitrate,  but  when 
the  mercury  is  in  excess,  more  or  less  basic  mercurous  nitrate  is  formed; 
hot  dilute  nitric  acid,  in  excess,  forms  chiefly  mercuric  nitrate;  when 
the  mercury  is  in  excess,  both  basic  mercurous  and  basic  mercuric 
nitrates  are  formed.    In  all  cases,  chiefly  nitric  oxide  gas  is  evob'ed. 

Alloys. — ]Mercury  unites  readily  with  most  metals  except  iron  and 
platinum.  With  the  former  it  has  been  found  to  unite  only  indirectly; 
for  example,  by  rubbing  very  finelv  divided  iron  with  mercuric  chloride, 
water,  and  a  few  drops  of  metallic  mercury.  The  latter  metal  can  only 
be  combined  in  the  spongy  state.  Yet  both  of  these  metallic  elements 
combine  chemically  with  mercury  to  form  definite  compounds,  accord- 
ing to  Bloxam  and  other  authorities,  and  present  the  composition  FeHg 
and  PtHg2  respectively. 

Vermilion. — Mercuric  sulphide,  HgS,  occurs  native  as  cinnabar,  a 
dull-red  mineral,  the  most  important  ore  of  mercury.  It  may  be  pre- 
pared by  several  different  methods,  much  depending  upon  the  purity 
of  the  materials  employed.  When  mercury  and  sulphur  are  heated 
together  their  imion  is  accompanied  with  much  energy,  and  if  the 
product  be  sublimed  the  red  or  mercuric  sulj)hide  is  obtained.  The 
sulphur  is  first  melted  and  the  mercury  gradually  added  by  straining 
through  linen  cloth,  whereby  it  falls  in  a  minutely  divided  state,  while 
the  mixture  is  constantly  stirred.  When  the  temperature  arrives  at  a 
certain  point,  the  combination  takes  place  suddenly  with  a  slight  explo- 
sion, attended  with  the  inflammation  of  the  sulphur,  which  must  be 
extinguished  by  covering  the  vessel.  The  product  of  the  combination 
is  a  black  mass,  generally  containing  an  excess  of  sulphur,  which, 
before  the  sul)limation  is  performed,  should  be  gotten  rid  of  by  gentle 
heat  on  a  sand  bath.  Sublimation  is  best  carried  on  in  a  closely  stopped 
glass  matrass,  which  should  be  placed  in  a  crucible  containing  sand, 
and,  when  thus  arranged,  exposed  to  a  red  heat.  The  resulting  ver- 
milion is  reduced  to  a  fine  powder  by  levigation,  the  beauty  of  the  tint 
depending  much  u{>on  the  extent  to  which  the  di\ision  is  carried. 

It  is  prepared  in  a  wet  way  l)y  intimately  mixing  100  parts  of  mer- 
cury with  38  parts  of  the  flowers  of  sulphur,  and  the  l)lack  sulphid 
of  mercury  thus  obtained  digested,  with  constant  agitation,  in  a  solu- 
tion of  25  parts  of  caustic  potash  in  150  parts  of  water  at  45°  C.  (the 
water  lost   by  evaporation    being   constantly  replaced),  until  the  pre- 


MERCURY.  137 

paratioii  has  come  up  to  its  maximum  of  fire  and  brilliancy,  which 
takes  a  good  many  hours.  Purely  sublimed  vermilion  has  a  compara- 
tively dull  color,  and  must  be  manipulated  with  an  alkaline  (jjotassium) 
sulphide  solution  to  give  it  the  necessary  fire.  The  action  of  the 
alkaline  sulphide  consists  probably  in  this,  that  it  dissolves  successive 
installments  of  the  amorphous  preparation  and  redeposits  them  in  the 
crystalline  form. 

Properties. — It  is  a  fine,  bright-scarlet  powder,  permanent  in  air, 
odorless  and  tasteless,  insoluble  in  water,  alcohol,  dikite  nitric,  con- 
centrated hydrochloric,  or  sulphuric  acids.  Nor  is  it  acted  upon  by 
boiling  potassium  hydrate,  sulphide  of  ammonium,  cyanide  of  potas- 
sium, or  sulphite  of  soda.  It  is  slightly  acted  upon  by  concentrated 
hot  nitric  acid,  and  completely  soluble  in  a  solution  of  potassium  sul- 
phide in  the  presence  of  free  alkali  or  a  solution  of  sodium  sulphide. 
Nitro-hydrochloric  acid  decomposes  it  into  mercuric  chloride,  which 
is  readily  soluble.  It  may  be  completely  sublimed,  as  has  been  seen, 
without  decomposition,  but  if  exposed  to  a  temperature  of  315.5°  C. 
(600°  F.)  it  is  decomposed  into  metallic  mercurv  and  sulphur  dioxide. 
It  is  frequently  adulterated  with  red  lead,  dragon's  blood,  chalk,  ferric 
oxide,  realgar  (As^S^),  and  brickdust.  If  lead  be  present  it  will  yield 
a  yellow  precipitate  when  digested  with  acetic  acid  and  potassium 
iodide  added.  Dragon's  blood  may  be  detected  by  alcohol,  which  will 
take  up  the  coloring  matter  of  that  substance  if  present.  Chalk  is 
detected  by  an  effervescence  on  the  addition  of  an  acid.  INIost  other 
impurities  may  be  detected  by  subliming  a  small  portion  of  the  com- 
pound. The  non-volatile  substances  used  for  adulteration  will  remain 
behind. 

Uses. — When  pure  it  is  much  used  as  a  pigment,  on  account  of  its 
brilliancy  and  color.  Its  unalterableness  and  resistance  to  chemical 
action  render  it  particularly  valuable  in  giving  the  red  color  to  vulcan- 
izable  rubber  used  in  the  construction  of  artificial  dentures  of  red  and 
pink  vulcanite,  in  the  composition  of  which  it  forms,  in  some  cases, 
about  one-third  of  the  entire  weight  of  the  compound.  Notwithstand- 
ing the  poisonous  character  of  mercurial  compounds  in  general,  and 
the  frequency  of  troubles  of  an  inflammatory  nature  of  the  mucous 
membrane  in  mouths  fitted  with  rubber  dentures,  it  is  obviously  very 
improbable,  when  we  consitler  the  properties  of  pure  vermilion,  that 
such  conditions  can  be  in  any  degree  attributable  to  the  presence  of 
this  substance  per  se.  It  is  quite  possible  that  impure  vermilion  may 
contain  from  the  start  free  mercury;  be  contaminated  with  arsenic 
bisulphide,  or  poisonous  adulterations.  Again,  the  practice  of  dis- 
solving tin-foil  off  of  the  surface  of  plates  with  nitro-hydrochloric  acid 
just  after  vulcanization  mav  possibly  decompose  some  little  vermilion, 
forming  soluble  bichloride.  It  Is  highly  improbable  that  any  of  these 
conditions  can  be  found,  yet  it  is  possible.  It  is  said  that  free  mercury 
has  been  observed  with  the  microscope  in  finished  \T.ilcanite.  The 
occurrence  of  oral  inflammatory  conditions,  under  black  rublier  den- 
tures, precisely  similar  to  those  under  red  rubber,  practically  relieves 
vermihon  of  the  responsibility.    Such  inflammatory  troubles  are  directly 


188     MF/r.\LS  AM)   ALLOYS    USKI)    IN  I'llOSTII lyi'lC   DF.yTISTIlY. 

attrihiitahlo  to  its  r()ii<^li  and  jjorous  surface,  lack  of  clcaiiliiu'ss  on  tlie 
part  of  the  wearer,  and  the  fact  that  rnhher  is  a  non-conductor  (*f  heat. 

ALUMINUM. 

Aluminum.  Symbol,  Al. 

Atomic  weignt,  2()9.  M;illeal)ility  (said  (o  equal  silver). 

Mcltiiifi  point  625°  (1157°  V.)  Tenacity,  fonrth  rank. 

Ductility,  eifihtli  rank.  Specific  gravity,  2.583. 

Conductivity  (heat),  100.  ("onducti\itv  "(electricity),  100. 

(Silver  heiufr  1  ()().) 

Occurrence. — With  the  exception  of  silicon  and  oxyfi;en,  aluminum 
is  tlie  most  al)undant  element  in  the  earth's  crust.  It  is  never  found 
in  the  free  or  metallic  state,  l)ut  occurs  combined  with  silicon  and 
oxyo;en,  as  marl,  clay,  slate,  pumice-stone,  feldspar,  mica,  and  nearly 
all  rocks,  with  the  exception  of  limestone  and  sandstone.  As  the  cry.s- 
tallized  oxide — alr.mina — it  occurs  as  corundum  (AI2O3),  emery,  ruby, 
sapphire,  emerald,  topaz,  and  amethyst,  which  are  used  as  gems.  The 
metal  i.s  further  found  in  combination  with  nearly  two  hundred  difTerent 
minerals. 

Properties. — Aluminum  is  a  bluish-white  metal,  somewhat  resem- 
bling silver  in  appearance.  It  is  also  said  to  be  as  malleable,  of  the  same 
tenacity,  and  equal  to  that  metal  in  the  conduction  of  heat  and  elec- 
tricity. It  is  harder  than  tin,  but  softer  than  copper.  By  hammering 
in  the  cold  it  may  be  made  as  hard  as  soft  iron,  but  is  softened  again 
by  fusion.  It  is  remarkably  sonorous,  and  has  been  used  for  making- 
bells.  It  is  one  of  the  lightest  of  metals,  being  approximately  only  two 
and  a  half  times  heavier  than  water,  and  four  times  lighter  than  silver. 
It  fuses  at  ()2o°  C,  or  about  1157°  F. ;  do€\s  not  oxidize  in  air,  even  at  a 
red  heat;  has  no  action  on  water  at  ordinary  temperatures,  nor  is  it 
acted  upon  by  the  compounds  of  sulphur,  thus  preserving  its  lustre 
where  silver  would  be  tarnished  and  blackened.  It  is  without  odor  or 
taste. 

Aluminum  may  be  melted  in  an  ordinary  clay  crucible,  no  flux  being 
needed.  Borax  is  not  only  useless,  but  is  actually  harmful,  as  aluminum 
readily  attacks  the  glasses.  Biederman  recommends  dipping  the 
scraps  which  are  to  be  melted  together  in  benzine  before  putting  them 
in  the  crucible.  Should  any  be  contaminated  with  solder  this  may  be 
removed  by  nitric  acid,  which  does  not  act  u])on  aluminum. 

Alloys. — Aluminum  alloys  with  nearl}^  all  metals,  except  lead;  in- 
deed, tiie  wonderful  alloys  it  is  capable  of  producing  gives  it,  perhaps, 
its  greatest  value. 

Aluminum  may  be  melted  in  a  graphite  crucible  without  flux,  but 
great  care  must  be  taken  not  to  heat  it  too  hot.  On  account  of  its  high 
specific  and  latent  heat,  aluminum  requires  a  long  time  to  melt;  but, 
unlike  some  other  metals,  it  soon  becomes  fluid  after  tlie  melting  point 
is  reached. 

Cold  and  aluminum  unite,  forming  a  hard  and  brittle  alloy.  One 
per  cent,  of  aluminum  in  gold  destroys  the  ductility  of  the  noble  metal 
and  gives  it  a  greenish  cast;  5  per  cent,  of  ahimimnn  with  gold  yields 


ALUMINUM.  139 

an   alloy   hrittlr  as  j^lass,  and   10  per  cont.  of   aluiiiimiiii    ])ro(ltice.s  a 
white,  frvstalliiu\  and  brittle  alloy. 

Niirnberg  gold,  an  alloy,  for  cheap  goldware,  very  much  resembling 
gold,  antl  unchanged  in  air,  is  composed  of  aluminum  7.5,  gold  2.5, 
and  copper  90  parts. 

Silver  and  aluminiun  readily  unite,  forming  alloys  of  beautiful  white- 
ness, and  unchangeable  on  exposure  to  air.  Their  hardness  is  con- 
siderably greater  than  aluminum,  but  they  are  more  easily  worked. 
An  alloy  of  100  parts  of  aluminum  and  5  parts  of  silver  diflfers  but  little 
from  piu-e  aUuninum,  save  that  it  is  considerably  harder  and  takes  a 
beautiful  polish.  An  alloy  of  aluminum  169  parts  and  silver  5  parts 
possesses  considerable  elasticity,  and  has  been  recommended  for  watch 
springs,  dessert  and  fruit  knives.  Equal  parts  of  the  two  metals  pro- 
duce an  alloy  equal  in  hardness  to  bronze. 

Copper  and  aluminum  for  some  exceedingly  important  alloys,  differ- 
ing according  to  the  quantity  of  aluminum  they  contain.  Those  of  a 
small  content  of  copper  cannot  be  used  industrially.  With  60  to  70 
per  cent,  of  aluminum  they  are  very  brittle,  glass-hard,  and  beautifully 
crystalline.  With  50  per  cent,  the  alloy  is  quite  soft;  but  under  30  per 
cent,  of  aluminum  the  hardness  returns.  The  usual  alloys  are  1,  2,  5 
and  10  percent,  of  aluminum.  These  are  known  as  aluminum  bronze. 
The  10  per  cent,  bronze  has  a  bright  golden  color  and  keeps  its  polish 
in  air;  it  may  be  easily  engraved,  shows  a  greater  elasticity  than  steel, 
and  can  be  easily  soldered  with  18-carat  gold  solder.  When  first  made 
it  is  brittle,  acquiring  its  best  qualities  after  three  or  four  meltings,  after 
which  it  may  be  melted  several  times  without  sensible  change.  It  casts 
well  in  sand  molds,  but  shrinks  greatly.  It  has  a  specific  gravity  of 
7.68,  about  equal  to  soft  iron.  Its  strength  when  hammered  will  equal 
that  of  the  best  steel.  Anneahng  makes  it  soft  and  malleable.  It  does 
not  clog  a  file,  and  may  be  drawn  into  ware.     It  melts  at  about  1700°  F. 

Aluminum  bronze  as  a  base  for  artificial  dentures:  "In  the  propor- 
tion of  aluminum  100  and  copper  900  it  oxidizes  but  superficially  in  the 
mouth,  and  is  as  strong  and  resistant  to  attrition  as  18-carat  gold;  it 
may  be  swaged  as  easily  as  20-carat  gold,  but  it  must  be  annealed  fre- 
quently, and  it  is  necessary  to  carry  the  heating  almost  to  whiteness, 
for  if  the  bronze  be  merely  heated  until  it  assumes  a  dark-red  color  it 
remains  as  hard  as  before."     (Professor  Saner.) 

The  alloys  of  copper  and  aluminum  are  prepared  in  the  Cowles 
electric  furnace  by  fusing  together  the  oxides  of  aluminum  and  metallic 
copper  with  enough  carbon  and  flux  to  reduce  them.    The  oxides  and 
other  materials  thould  be  as  finely  divided  as  possible. 

Solders. — The  difficulty  of  soldering  aluminum  prevented  the  metal 
from  being  applied  to  many  useful  purposes  for  some  time.  The  solder 
recommended  for  general  use  in  the  manufacture  of  articles  of  orna- 
mentation is  composed  of  copper,  4  parts;  aluminum,  6  parts;  zinc, 
90  parts.  The  use  of  this  requires  some  skill  and  experience;  no  borax 
is  used  and  the  adhesion  is  induced  by  the  friction  of  small  aluminum 
tools.  The  following  alloys  may  be  used  as  solders  for  articles  of  jewelry 
mad/?  of  10  per  cent,  aluminum  bronze: 


140     METALS  AND  ALLOYS  I'SKD  IS  I'liOSTHETIC  DENTISTRY. 


Gold 

Silver 

Copper 

Gold 

Silver 

C'opp(>r 


Hard  Solder. 


Medium  Hard  Solder. 


88.88  per  cent. 
4.68 
6.44 


54.40  per  cent. 

27.00 

18.00 


Mr.    Wm.    Frismiith,    of   Philadelphia,   recommends   the   following 
solders  for  aluminum,  with  vaselin  as  the  flux: 

Soft  Solder. 
Pure  block  tin  ....      from  90  to  99  part.s. 


Bismuth  . 

Pure  block  tin 
Bismuth  . 
Aluminum 


Hard  Solder. 


10   "     1 


from  98  to  90  parts. 
"        1    "     5      " 
1    "     5      " 


Schlosser  recommends  the  following  for  dental  laboratory  use : 

Pl.\tinum-Alu.minum  Solder. 
Gold     .... 
Platinum 

Silver    .... 
Almninum 


Gold  . 
Silver  . 
Copper . 
Aluminum 


Gold-.\luminum  Solder. 


30 

parts. 

1 

part. 

20 
00 

parts. 

50 

parts. 

10 

•     ii 

10 

" 

20 

" 

O.  M.  Thowless  has  patented  the  following  solder  for  aluminum 
and  the  method  of  applying  it: 


Tin 
Zinc 
Silver    . 
Aluminum 


55  parts. 
23      " 

5      " 

2      " 


First  melt  the  silver  and  aluminum  together  then  add  the  tin  and 
zinc  in  the  order  named.  The  surfaces  to  be  soldered  are  immersed 
in  dilute  caustic  alkali  or  a  cyanide  solution,  and  then  washed  and 
dried.  They  are  next  heated  over  a  spirit  lamp,  coated  with  the  solder, 
and  clamped  together;  small  pieces  of  solder  being  placed  at  the  points 
of  union,  the  whole  is  then  heated  to  the  melting  point.  No  flux  is 
used. 

The  following  are  useful  as  solders: 


Zinc 

Aluminum 


The  flux  used  in  soldering  is  composed  of  3  parts  balsam  of  copaiba, 
1  part  Venetian  turpentine,  and  a  few  drops  of  lemon-juice.  The 
soldering  iron  is  dipped  into  the  mixture.  So  far,  the  soldering  of 
aluminum  in  the  dental  laboratory  is  very  difficult  and  unsatisfactory. 


I. 

II. 

III. 

80  parts. 

85  parts. 

92  parts 

20      " 

15     " 

8      " 

ALUMINUM.  141 

Another  solder  for  aluminum,  recommended  by  the  Scientific  Ameri' 
can,  is  composed  of  the  following: 

Cadmium         .......     50  parts. 

Zinc 20      " 

Tift 30      " 

The  zinc  is  first  melted  in  a  suitable  vessel;  then  the  cadmium  is 
added,  and  then  the  tin,  in  small  pieces.  The  proportions  of  the  vari- 
ous ingredients  may  be  varied,  in  accordance  with  the  use  to  which 
the  article  is  put.  For  instance,  when  a  strong  and  tenacious  solder- 
ing is  required,  a  larger  proportion  of  cadmium  can  be  used;  where 
great  adhesion  is  desired,  a  large  proportion  of  zinc  should  be  used, 
and  where  a  nice  and  durable  polish  is  desired  a  greater  per  cent,  of 
tin  should  be  used. 

An  alloy  of  zinc,  copper,  and  aluminum  has  been  introduced  as  a 
dental  base.  (See  also  Carroll's  alloys  for  cast  dentures,  Chapter  XV.) 
It  is  said  to  be  unaffected  by  the  oral  fluids. 

Tin  and  aluminum  form  alloys  little  affected  by  acids.  With  100 
parts  aluminum  and  10  parts  tin  an  alloy  is  produced  much  whiter 
than  aluminum  and  but  little  heavier.  It  can  be  welded  and  soldered 
like  brass. 

Iron  and  aluminum  unite  readily.  Ostberg,  a  Swedish  inventor, 
discovered  that  an  exceedingly  small  content  of  aluminum  (two" 
of  1  per  cent.)  in  wrought  iron  served  to  lower  its  fusing  point  about 
500°  F.,  so  that  castings  may  be  made  from  it  as  readily  as  fiom  the 
highly  carburized  cast  iron.  Iron  may  be  coated  with  aluminum  much 
as  it  is  with  tin. 

Zinc  and  aluminum  unite  to  form  alloys  very  useful  for  soldering  the 
latter.  They  are  prepared  by  first  melting  the  aluminum  and  adding 
the  zinc  gradually,  after  which  some  fat  is  introduced  to  prevent  oxida- 
tion, and  the  alloy  is  stirred  rapidly  with  an  iron  rod.  Aluminum  may 
be  frosted  by  immersion  in  a  solution  of  potassa. 

IRON. 

Ferrum.  Symbol,  Fe. 

Atomic  weight,  55.5.  Malleability,  ninth  rank. 

Melting  point,  1600°  (2912°  F.).  Tenacitj^  first  rank. 

Ductility,  fourth  rank.  Specific  gravity,  7.844. 

Conductivity  (heat),  11.9.  Conductivity  (electricity),  16.81. 

(Silver  being  100.) 

Occurrence. — Iron  is  widely  and  abundantly  distributed  throughout 
nature,  being  found  in  nearly  all  forms  of  rock,  clay,  sand,  and  earth; 
its  presence  in  these  being  commonly  indicated  by  their  colors,  for  iron 
is  tke  commonest  of  all  natural  mineral  coloring  ingredients. 

Properties. — Pure  iron  is  a  hard,  malleable,  ductile,  and  tenacious" 
metal,  of  a  grayish-white  color,  and  of  fibrous  texture,  slightly  styptic 
taste,  and  has  a  sensible  odor  when  rubbed.  Its  strength  and  tenacity 
are  very  high.  In  magnetic  properties  it  is  superior  to  all  other  sub- 
stancesl!  nickel  and  cobalt  being  next;  when  it  is  almost  pure,  the  mag- 
netic influence  produced,  owing  to  induction,  by  the  proximity  of  a 


142     METALS  AM)   ALLOYS   USFP   fX   PROSTnETK'  DEXTLSTRY. 

permanent  ninf^net  or  of  an  electric  current,  disappears  entirely  on 
removal  of  the  magnet  or  current;  if,  on  the  other  hand,  carbon  be 
present  (as  is  usually  the  ca.se  to  some  small  extent  even  in  the  softest 
malleable  iron),  there  remains  after  the  remo^'al  of  the  magnet  or  cur- 
rent a  greater  or  less  amount  of  permanent  magnetism,  according  to 
the  circumstances,  hard  steel  exhibiting  the  greatest  power  of  becoming 
permanently  magnetized  under  given  conditions.  In  thermic  and 
electric  conductivity  iron  is  rated  at  11.9  and  1(1. SI,  respectively.  Its 
specific  gravity  is  7.844,  its  specific  heat  0.113(S,  and  its  melting  point 
is  variously  estimated  from  1500°  to  1000°  C.  (Pouillet)  to  1<)00°  to 
2000°  C.  (Deville).  The  presence  of  minute  fjuantities  of  carbon,  sul- 
phur, etc.,  very  sensiWy  lowers  the  fusing  point,  while  1  per  cent,  of 
the  former  furnishes  a  steel  melting  at  several  hundred  degrees  lower 
than  pure  iron.  Cast  iron,  containing  more  carbon,  melts  very  much 
lower.  It  possesses  the  remarkable  property  of  becoming  plastic  just 
before  fusion,  so  that  two  hot  masses  may  be  pressed  or  scjueezed 
together  into  one  by  the  process  of  welding.  So  by  forging,  rolling, 
hammering,  or  other  analogous  operations,  it  can  readily  be  fashioned 
into  shapes  which  its  rigidity  and  strength  when  cold  will  enable  it  to 
maintain. 

Modifications  of  Iron. — There  are  three  distinct  modifications  of 
iron,  viz.,  cast  iron,  wrought  iron  and  steel.  Other  intermediate  varie- 
ties are  recognized  technically,  but  all  are  closely  related  and  impercep- 
tibly shaded  into  each  other,  due  to  various  percentages  of  carbon, 
etc.,  contained  in  the  metal. 

Cast  iron  is  an  impure  carburized  iron.  The  melted  metal  drawn 
off  from  the  furnace  below  is  conducted  into  a  large  main,  called  the 
"sow,"  and  thence  into  lateral  molds  called  "pigs;"  hence  the  term 
pig  iron.  This  iron  is  found  to  have  combined  with  a  considerable 
(juantity  of  carbon,  aljout  4.5  per  cent,  being  the  maximum;  a  portion 
of  which  exists  as  a  chemical  combination,  the  carbide  of  iron,  the 
remainder  having  been  simply  dissolved  in  the  form  of  graphite.  Other 
substances  in  the  furnace  are  also  found  dissolved  and  combined  in 
the  iron,  and  have  an  important  bearing  upon  its  physical  properties. 
These  are  principally  phosphorus,  silicon,  sulphur,  manganese,  etc. 

Pig  iron  may,  therefore,  be  recognized  as  a  crude  form  of  cast  iron. 
It  is  assorted  and  classed  by  the  iron  masters  as  Nos.  1,  2,  and  3,  differ- 
ing in  the  amount  of  carbon  contained.  No.  1  is  most  highly  carburized, 
No.  2  less,  and  No.  3  contains  the  least  carbon.  The  first  melts  and 
becomes  so  fluid  that  it  is  used  for  ornamental  castings  of  fine  pattern, 
and  furnishes  cast-iron  cutlery  from  which  the  carbon  is  subsequently 
extracted. 

Cast  iron,  which  contains  the  most  carbon,  is  the  most  fusible  variety, 
melting  at  about  1200°  C.  It  is  hard  and  l)rittle.  Though  some  kinds 
admit  of  beintj  made  hard  or  soft  nearlv  in  the  same  manner  as  steel, 
and,  like  steel,  assume  different  degrees  of  hardness,  according  to 
the  rapidity  with  which  the  pieces  are  allowed  to  cool;  but  unlike  steel, 
when  once  hardened,  will  not  admit  of  that  hardness  being  reduced 
by  various  gradations  to  any  specific  degree,  called  tempering.     To 


FRON.  143 

softcMi  niivteviallv  it  nv.ist  hv  siil)inittcd  for  some  time  to  a  whitish  licat, 
and  thcMi  very  gradually  cooled. 

Wrought  iron  is  the  cast,  or  pig,  iron,  freed  from  carbon,  and  may  be 
considered  a  nearly  pure  decarburized  iron;  at  least,  it  is  the  purest 
form  of  commercial  iron,  containing  the  least  amount  of  car})on — less 
than  {  per  cent.  The  decarburization  is  effected  by  first  remelting  the 
pig  or  cast  iron,  and  refining  by  exposing  it  to  an  intense  heat  and 
forcing  a  blast  of  air  over  its  surface,  in  order  to  remove  some  of  the 
impurites  of  the  metal;  it  is  then  run  out  into  a  large  flat  mold,  and 
acquires  the  name  of  plate  metal. 

The  next  process  is  called  "puddling,"  the  object  being  to  free  the 
metal  of  its  carbon.  The  operation  is  conducted  in  a  reverberatory 
furnace,  where  the  metal  is  again  reheated  and  converted  into  wrought 
iron  by  keeping  it  in  a  state  of  fusion  with  a  certain  amount  of  black 
oxide  of  iron,  FcgO^,  which  gives  up  its  oxygen  after  a  time  to  the  car- 
bon, and  other  impurities  of  the  melted  mass,  leaving  the  latter  nearly 
pure  iron.  As  the  process  approaches  termination  the  fusing  point  of 
the  mass  grows  higher,  until  it  loses  nearly  all  its  fluidity.  It  is  then 
divided  into  several  parts  and  formed  into  balls,  which  are  removed 
from  the  furnace  and  subjected  to  intense  pressure  through  a  series  of 
powerful  rollers,  which  squeeze  out  the  more  fusible  slag  entangled 
in  it  and  convert  it  into  bars  or  "bloom."  A  number  of  these  blooms 
are  then  raised  to  a  welding  heat  and  repeatedly  passed  through  rollers, 
until  all  the  remaining  slag  is  forced  out  and  the  metal  becomes  tough 
and  fibrous.  Thus  the  process  is  repeated  usually  once,  and  some- 
times twice  or  three  times,  to  produce  a  superior  iron.  By  this  process 
the  metal  is  converted  from  a  fusible,  hard,  and  brittle  substance,  as 
cast  iron,  into  a  tough,  elastic  bar ;  in  fact,  it  has  been  rendered  malle- 
able, ductile,  more  closely  compact,  and  of  a  fibrous  texture,  and  is 
less  fusible.  It  is  also  very  tenacious,  and  added  to  its  properties  is  a 
new  and  remarkable  one,  by  virtue  of  which  two  pieces  being  heated 
similarly  may  be  forged  or  welded  together.  For  purposes  where  light- 
ness, strength,  and  durability  are  wanted,  it  is  more  extensively  em- 
ployed than  cast  iron.  In  this  state  it  is  known  in  commerce  as  bar,  or 
wrought  iron. 

Steel  is  composed  of  iron  and  carbon,  and,  generally  speaking,  it  is 
prepared  by  either  one  of  two  ways:  by  adding  a  certain  percentage 
of  carbon  to  a  lightly  carburized  iron,  such  as  wrought  iron;  or  by 
abstracting  an  amount  of  carbon  from  a  heavily  carburized  iron,  such 
as  cast  iron.  This  fact  gave  rise  to  two  typical  methods  of  preparing 
steel,  viz.,  the  cementation  process  and  the  Bessemer  process.  While 
technically  there  are  a  variety  of  methods  by  which  steel  is  made,  yet 
all  methods  are  more  or  less  modifications  of  these  two  typical  ones. 
The  proportion  of  carbon  varies,  of  course,  in  the  different  qualities  of 
steel;  but  in  that  used  ordinarily  the  carbon  rarely  exceeds  IV  per  cent.; 
for  some  purposes  it  is  as  low  as  1  per  cent.  Good  ordinary  tool  steel 
contains  about  1 V  per  cent,  of  carbon.  Different  kinds  of  iron  produce 
steel  of  different  properties,  and  different  qualities  of  steel  are  used  for 
different  purposes. 


144     METALS  AND  ALLOYS   USED  IN  PROSTHETIC  DENTISTRY. 

Bessemer's  Process. — By  this  process  steel  can  be  maiuifactured 
of  anv  degree  of  hardness  directly  from  the  cast  iron,  without  the  inter- 
mediate operation  of  making  it  malleable  by  puddling,  etc.  The  prin- 
ciple of  the  process  consists  in  directing  a  blast  of  cold  air  upon  molten 
cast  iron  contained  in  a  "converter."  The  oxygen  of  the  blast  combines 
with  the  carbon,  silicon,  and  manganese.  Sulphur  and  phosphorus 
are  difficult  to  remove  by  this  process;  hence  the  necessity  of  emj)loying 
ores  as  free  from  these  as  possible.  The  intense  combustion  of  the 
carbon  in  th".  iron  is  attended  with  great  elevation  of  temperature,  so 
that  the  metal  is  maintained  in  a  fluid  state  throughout  the  whole 
operation,  solely  by  the  energy  of  the  reaction  in  the  converter.  Thus 
the  cast  or  pig  iron  is  decarburized,  or  converted  into  tool  steel,  or  to 
mild  welding  steel,  or  to  the  state  of  malleable  iron,  according  to  the 
length  of  time  the  combustion  is  continued.  It  has  been  found,  how- 
ever, that  a  better  (piality  of  steel  can  be  produced  by  contimiing  the 
decarburizing  and  purifying  process  until  all,  or  as  nearly  all  as  possi- 
ble, of  the  carljon  and  impurities  are  removed,  and  then  adding  to  the 
fused  wrought  iron  a  certain  quantity  of  a  peculiar  kind  of  white  cast 
iron  known  as  spiegel-eisen^  ("looking-glass"  iron),  containing  a  known 
quantity  of  carbon  and  a  little  manganesium  and  silicon. 

Bessemer  steel  is  largely  used  in  the  construction  of  railroads,  bridges, 
armor  plates  for  vessels,  girders,  etc.,  in  the  construction  of  edifices, 
the  manufacture  of  machinery,  tools,  etc.,  and  there  is  good  reason  to 
believe  that  steel  of  an  excellent  cpiality  for  numerous  purposes  will, 
at  no  distant  period,  be  manufactured  cheaper  than  wrought  iron  is 
now  produced  by  the  operation  of  puddling. 

The  Cementation  Process. — The  furnace  in  which  the  iron  is 
cemented  and  converted  into  steel,  called  a  converting  furnace,  has 
the  form  of  a  large  oven,  constructed  so  as  to  form  in  its  interior  two 
large  and  long  cases,  commonly  called  troughs  or  pots,  and  built  of 
good  fire-stone  or  fire-brick.  Into  each  of  these  pots  layers  of  the  purest 
malleable  iron  bars  and  layers  of  pulverized  charcoal  are  packed  hori- 
zontally, one  upon  the  other,  to  a  proper  height  and  (juantity,  according 
to  the  size  of  the  pots,  leaving  room  every  way  in  them  for  the  expansion 
of  the  metal  when  it  becomes  heated.  After  the  packing  is  completed 
the  tops  are  covered  with  a  bed  of  sand  or  clay.  This  is  to  confine 
the  carbon  and  exclude  the  atmosphere.  The  whole  is  then  heated 
for  eight  or  ten  days,  according  to  the  degree  of  hardness  recjuired. 
Then  the  mass  is  left  to  cool  for  several  days. 

The  properties  of  the  iron  are  remarkably  changed  by  this  process: 
it  acquires  a  small  addition  to  its  weight,  becomes  much  more  brittle 
and  fusible  than  originally,  loses  much  of  its  ductility  and  malleability, 
but  gains  in  hardness,  elasticity,  and  sonorousness.  The  texture, 
which  was  fibrous  before,  has  now  become  granular;  and  its  surface  is 
found  to  be  covered  with  blisters,   and  it  presents,  when   broken,  a 

'  Spiegel-eisen  is  composed  of  the  following: 

Iron 82.86 

Manganesium    ..........  10.71 

Silicon 1.00 

Carbon 4.32 


IRON.  145 

fracture  much  like  inferior  iron.  Iron  under  this  process  has  been 
shown  to  have  taken  up  about  1  per  cent,  of  carbon.  It  is,  however, 
far  from  beino-  homogeneous  in  composition,  and  is  called  blister  steel. 
Uniformity  of  composition  is  secured  by  subjecting  bundles  of  the 
carburized  bars  to  repeated  blows  from  a  steam  hannner  at  a  welding 
heat,  striking  in  rapid  succession,  until  it  closes  the  seams  and  removes 
the  blisters.  It  is  then  termed  shear  steel.  After  this  treatment  is  re- 
peated it  is  called  d()ul)k -shear  steel.  Homogeneity  is  best  ol)tained, 
however,  by  fusing  the  blister  steel  in  crucibles,  covering  the  mass  with 
clay  or  some  other  substance  to  exclude  air,  and  casting  it  into  ingots. 
It  is  then  designated  as  cast  steel  or  crucible  steel. 

Spring  steel  is  blister  steel  simply  heated  and  rolled. 

Case  hardening  is  accomplished  by  heating  such  articles  of  forged 
or  bar  iron,  as  it  is  desired  to  harden  superficially,  in  contact  with  some 
substance  rich  in  carbon,  and  afterward  chilling  them  in  water.  Gun- 
locks  are  thus  treated. 

Harveyized  steel,  which  is  employed  for  armor  plate  on  account 
of  its  extremely  hard  and  resistant  surface,  is  prepared  by  heating  the 
steel  plate  to  the  melting  point  of  cast  iron  and  then  tightly  packing  its 
surface  with  carbon;  after  it  has  taken  up  about  1  per  cent,  of  the  car- 
bon the  plate  is  dropped  into  water  and  cooled. 

Nickel  Steel. — In  1889,  M.  Henry  Schneider,  of  Creusot,  France, 
patented  an  alloy  of  steel  and  nickel.  The  alloy  usually  contains  about 
5  per  cent,  of  nickel,  and  is  especially  suitable  for  use  in  the  construc- 
tion of  ordnance,  armor  plate,  gun-barrels,  and  projectiles.  It  is  said 
that  ordinary  steel  is  more  readily  acted  upon  by  sea-water  than  are 
the  more  impure  grades  of  iron,  but  nickel  steel  is  less  liable  to  corrode 
in  salt  water  than  ordinary  steel. 

Manganese  Steel. — When  about  15  per  cent,  of  manganese  is 
added  to  steel  it  produces  an  alloy  of  great  strength  and  toughness, 
and  so  hard  that  it  is  almost  impossible  to  work  the  product  by  ordinary 
methods.  The  alloy  is  usually  prepared  by  adding  manganese  iron 
to  molten  Bessemer,  or  open-hearth  steel.  From  4  to  5  per  cent,  of 
manganese  gives  to  the  alloy  its  extreme  brittleness.  Extremes  of  atmos- 
phere, heat  or  cold,  do  not  appear  to  affect  the  properties  of  manganese 
steel.  When  a  piece  of  it  heated  sufficiently  to  be  seen  red  hot  in  a 
dark  room  is  plunged  into  cold  water,  it  becomes  soft  enough  to  be 
easily  filed.  Hardness  is  then  restored  by  reheating  to  a  bright  red 
and  cooling  in  air.  The  presence  of  manganese  in  proper  proportions 
in  nickel  steel  is  said  to  very  much  improve  it.  Indeed,  the  best  results 
are  only  obtained  by  the  admixture. 

Chrome  Steel. — Chromium  gives  greater  hardness,  tensile  strength, 
and  elasticity  to  iron,  but  decreases  its  weldability.  It  is  also  stated 
that  chromium  steel  is  more  susceptible  of  oxidation  than  ordinary 
steel.  Chromium  is  added  to  iron  by  heating  the  mixed  oxides  of  iron 
and  chromium  in  a  brasqued  crucible  with  pulverized  charcoal  and 
fluxes.  Chrome  steel  is  then  produced  by  melting  chrome  iron  with 
wrought  iron  or  steel  in  graphite  crucibles. 

Copper  Steel. — This  alloy  usually  contains  from  5  to  20  per  cent. 

10 


146     METALS  AND   ALLOYS   USED   IN  PROSTHETIC  DENTISTRY. 

of  copper,  according  to  the  })iirp().se  for  which  it  is  to  be  used.  It  pos- 
sesses remarkable  streiif^th,  tenacity,  and  malleabihty,  and  these  prop- 
erties are  still  further  developed  by  tempering. 

Aluminum  Steel. — In  amounts  not  greater  than  1  per  cent,  alum- 
inum is  said  to  slightly  increase  the  tensile  strength,  and  proportionally 
the  elastic  limit,  of  rolled  and  cast  steel. 

Tungsten  in  small  (juantities  produces  an  exceedingly  hard  steel, 
without  the  necessity  of  tempering. 

Carburized  Iron. — As  has  been  previously  hinted,  carbon  may 
be  present  in  iron  under  two  conditions.  AVhen  iron  is  fused  in  contact 
with  carbon  it  is  capable  of  combining  with  nearly  G  per  cent,  of  the 
latter  element  to  form  a  white,  brilliant,  and  brittle  compound,  which 
may  be  represented  pretty  nearly  as  Fe^C.  Under  certain  circum- 
stances, as  this  compound  of  iron  and  carbon  cools,  a  portion  of  the 
carbon  separates  from  the  iron  and  remains  disseminated  throughout 
the  mass  in  the  form  of  minute  crystalline  particles  very  much  resem- 
bling natural  graphite. 

Iron  containing  the  least  possible  carbon,  and  otherwise  compara- 
tively pure,  is  called  wrought  iron. 

Iron  containing  from  1.04  to  4.81  per  cent,  of  carbon  is  designated 
as  cast  iron. 

Iron  containing  from  0.15  to  1.04  per  cent.  (Bloxam)  is  considered 
steel.  "The  portion  of  combined  carbon  within  certain  limits  bears 
a  direct  relation  to  the  tensile  strength  of  the  metal,  variations  as 
minute  as  y^Q-  of  1  per  cent,  making  a  considerable  alteration  in 
this  quality.  The  same  is  true  of  hardness,  the  effect  of  carbon  up  to  a 
certain  point  being  to  increase  tenacity  and  decrease  ductility,  and  also 
to  cause  the  metal,  when  heated  and  suddenly  cooled,  to  become  more 
or  less  hard,  the  hardening  being  in  direct  proportion  to  the  amount  of 
carbon  present  and  the  rate  of  cooling."* 

1.4  per  cent,  of  carbon  in  iron  produces  a  highly  carburized  steel 
that  must  be  worked  with  great  care.  It  should  not  be  heated  above 
a  cherry-red,  for  fear  of  burning.  Such  steel  is  used  for  the  manufac- 
ture of  razors  and  tools  for  cutting  hard  metals. 

Steel  containing  from  1  to  1.25  per  cent,  of  carbon  is  used  for  making 
most  tools. 

Steel  containing  about  1  per  cent,  of  carbon  can  be  welded  readily, 
and  a  portion  of  a  tool  made  of  it  can  be  made  tough,  so  as  to  stand  a 
blow  from  a  hammer,  without  chipping,  while  another  part  can  be  hard- 
ened, as  in  the  case  of  a  cold-chisel. 

Hardening  and  Tempering  Steel. — After  soft  steel  has  been 
shaped  into  the  form  of  instrument  desired,  it  may  be  made  very  hard 
by  first  heating  to  redness  and  then  immediately  chilling  by  plungi-^g 
into  cool  w^ater,  oil,  or  mercury.  If,  however,  the  hardened  steel  be 
heated  to  redness  again  and  allowed  to  cool  slowly,  it  returns  to  its 
soft  condition.  Any  desired  variation  between  these  two  extremes 
may  be  obtained  by  heating  the  steel  to  redness  and  (juickly  chilling  it, 
thus  obtaining  the  full  hard  state.     If   this  be  polished  and  heated 

>  Kirk,  American  System  of  Dentistry,  vol.  iii.  p.  900. 


IRON.  lAl 

gradually  aiul  carefully,  it  will  be  foiuid  to  take  ou  a  sucee.s.sion  of 
shades  and  colors,  owing  to  the  formation  of  a  film  of  oxide  which 
grows  thicker  and  of  deeper  shade  and  color  as  the  heating  progresses. 
The  temperature  at  which  given  degrees  of  temper  are  produced  has 
been  carefully  determined,  and  the  experienced  operator  knows  by  the 
shade  or  color  of  the  film  of  oxide  the  temper  of  the  instrument  operated 
upon,  provided  the  piece  is  known  to  be  steel  and  to  have  been  full 
hard. 

The  following  table  shows  the  approximate  temperatures  corre- 
sponding to  the  various  shades  and  colors : 

Temperature.                                                   Color.  Temper. 

430°  to  450°  F.            .          .      Very  faint  yellow  Lancets,  razors,  surgical  instru- 

to  pale  straw.  ments,  enamel  chisels. 

470°  .  ■  .  .  .  Full  yellow.  Excavators,  very  small  cold- 
chisels. 

490°          ....      Brown.  Pluggers,  scissors,  pen-knives. 

510°  ....  Brown  with  pur-  Axes,  plain  irons,  saws,  cold- 
pie  spots.  chisels. 

530°         ....     Purple.  Table  knives,  large  shears. 

550°          ....      Bright  blue.  Swords,  watch-springs. 

560°          ....      Full  blue.  Fine  saws,  augers. 

600°          ....      Dark  blue.  Hand  and  pit  saws. 

Since  the  amount  of  hardness  which  can  be  developed  in  steel  is 
directly  in  proportion  to  the  amount  of  carbon  and  rate  of  cooling  the 
article  from  the  heated  condition,  and  as  pieces  of  steel  vary  greatly 
in  their  content  of  carbon,  the  temperature  at  which  it  is  necessary  to 
heat  them  before  chilling  must  be  determined  by  actual  experiment, 
in  order  to  produce  the  greatest  hardness.  The  piece  should  never  be 
overheated.  It  is  better  to  err  upon  the  side  of  underheating  instead  of 
overheating,  for  under  the  latter  condition  the  steel  is  burned,  presents 
a  blistered,  scaly  appearance,  and  is  incapable  of  taking  a  fine  tempr. 
Wlien  small  instruments,  such  as  burs,  excavators,  etc.,  are  to  be  hard- 
ened, it  is  best  to  protect  the  surface  of  the  steel  with  some  substance 
to  prevent  a  loss  of  carbon  by  oxidation  in  the  heating.  "Common 
soap  answers  admirably  for  this  purpose,"  says  Dr.  Kirk. 

The  means  of  applying  the  heat  to  articles  when  they  require  hard- 
ening will,  of  course,  depend  upon  the  size,  shape,  and  use  of  the  article. 
They  may  be  heated  in  the  flame  of  the  Bunsen  burner,  alcohol  lamp, 
open  fire,  and  sometimes  it  is  best  to  enclose  them  in  a  sheet-iron  case 
with  carbon,  and  heat  in  a  suitable  furnace;  but  for  a  more  uniform 
degree  of  heat  red-hot  lead  is  probably  better  than  any  other  means. 

In  chilling,  water  is  by  no  means  essential,  as  the  sole  object  is  to 
extract  the  heat  as  rapidly  as  possible  by  good  conduction;  and  the 
more  suddenly  the  heat  is  extracted,  the  harder  the  steel  will  be;  but  if 
the  hardness  is  not  carried  to  an  extreme,  a  certain  amount  of  tenacity 
is  also  obtained  with  the  hardness. 

Water  with  a  small  amount  of  acid  or  salt  is  sometimes  used,  the 
former  to  aid  in  removing  the  oxide,  and  the  latter  to  increase  the  con- 
ductivity. For  extreme  hardness  mercury  is  used,  which,  on  account 
of  its  superior  conductivity,  chills  the  piece  immediately. 


148     METALS  AND   ALLOYS    USED   IN  PROSTHETIC  DENTISTRY. 

Tempering. — A  rod  of  good  steel  in  its  hardest  state  is  broken  almost 
as  easily  as  a  rod  of  glass  of  the  same  dimensions.  This  brittleness 
can  only  be  diminished  by  decrecising  its  hardness;  and  the  manage- 
ment of  this  is  ealled  tempering.  The  snrfaee  of  the  steel  is  brightened 
and  tried  with  a  fine  file  to  make  sure  of  its  full-hardness,  and  is  then 
exposed  to  the  heat,  which,  upon  the  appearance  of  the  color  desired 
and  previously  determined  upon,  is  discontinued,  and  the  article  cooled 
by  instantly  plungmg  into  cool  water.  Tlie  methods  for  applying  the 
heat  for  tempering  are  as  varied  as  those  for  hardening.  The  heat  for 
this  purpose  should  be  slowly  applied;  indeed,  it  is  said  that  the  slower 
the  heating,  the  tougher  and  stronger  will  be  the  steel.  The  article 
may  be  placed  upon  a  hot  iron  plate,  upon  the  surface  of  melted  lead, 
or  in  a  bath  of  a  more  fusible  alloy;  in  hot  sand,  a  gas  stove,  or  in  almost 
any  place  where  sufficient  temperature  may  be  gradually  obtained, 
without  injury  to  the  steel. 

The  following  table  of  alloys  of  lead  and  tin  may  be  conveniently 
used  to  secure  a  imiform  temper: 

MeltinK  points. 
Degrees  F. 

-120° 

430° 

4.50° 

470° 

490° 

-510° 

530° 

550° 

560° 

600° 

(Compare  tjie  degrees  with  the  colors  of  the  previous  table.) 

When  instruments  are  only  partially  dipped  and  afterward  tem- 
pered by  the  heat  from  the  back,  they  must  be  cooled  in  water,  or  other 
substance,  instantly  on  the  cutting  part  attaining  the  desired  color; 
otherwise  the  body  of  the  instrument  will  continue  to  supply  heat,  and 
the  cutting  part  may  become  too  soft.  In  the  case  of  excavators,  enamel 
chisels,  and  cutting  instruments  with  slender,  tapering  shanks,  ter- 
minating in  a  fine  cutting  edge,  the  edge  must  be  protected  from  the 
heat  while  tempering  the  shank,  the  latter  being  drawn  to  a  blue,  a 
state  much  too  soft  for  the  former.  The  point  or  edge  may  be  protected 
by  placing  against  a  large  piece  of  cold  iron  or  other  subtance  which, 
on  account  of  its  conduction,  prevents  the  heating  of  the  end  of  the 
instrument. 

Rubber-dam  clamps  are  best  tempered  a  blue  spring  by  what  is 
known  as  blazing  off.  This  is  accomplished  by  dipping  them  in  oil, 
and  then  burning  the  oil  off. 

Action  of  Acids  on  Iron. — Iron  dissolves  in  the  acids,  and  the  car- 
bon  which  it  almays  contains,  so  far  as  combined  in  the  carbide  of  iron, 
passes  oflP  as  carburetted  hydrogen,  and  so  far  as  uncombined  will 
remain  undissolved,  as  graphite. 


Composition 

Lead. 

Tin. 

7.0 

4 

7.5 

4 

8.5 

4 

10.0 

4 

14.0 

4 

19.0 

4 

30.0 

4 

48.0 

4 

50.0 

4 

Boiling  oil 

COPPER.  149 


COPPER. 


Cuprum.  Symbol,  Cu. 

Atomic  weight,  63.1.  Malleability,  third  rank. 

Melting  point,  1200°  (2192°  ¥.).  Tenacity,  second  rank. 

Ductility,  fifth  rank.  Specitic  gravity,  8.94. 

Conductivity  (heat),  73.6.  Conductivity  (electricity),  99.95. 

(Silver  being  100.) 

Occurrence. — This  exceedingly  interesting  and  useful  metal  ha.s 
been  known  and  used  by  the  human  race  since  the  most  remote  periods. 
Its  alloy  of  tin-bronze  was  the  first  metallic  compound  used  by  man. 
It  is  found  in  the  metallic  state  in  the  Lake  Superior  region,  and  in 
Mrginia,  the  southwestern  portion  of  the  United  States,  and  many 
other  parts  of  the  world. 

Properties. — Copper,  or  cuprum,  in  name  is  derived  from  Kupros, 
the  Greek  spelling  of  Cyprus,  an  island  where  it  is  extensively  mined. 
Its  symbol  is  the  planet  ^>nus,  as  the  isle  of  Cyprus  was  sacred  to  that 
goddess.  It  is  a  peculiar  red-colored,  brilliant  metal,  differing  in  this 
respect  from  all  other  metallic  elements,  except,  perhaps,  titanium. 
Its  atomic  weight  is  63.1,  and  its  specific  gravity  8.94.  It  takes  a 
brilliant  polish,  and  is  very  malleable  and  ductile,  being  second  to  iron 
in  point  of  tenacity.  It  may  be  rolled  into  thin  sheets  or  drawn  into 
very  fine  wire.  A  copper  wire,  hard  draw'n,  having  a  sectional  area 
of  a  square  millimetre,  sustained  a  weight  of  90.20  pounds  at  the  moment 
of  rupture.  The  same  wire,  annealed,  broke  under  a  weight  of  69.52 
pounds,^  The  melting  point  of  copper  is  probably  best  stated  at  1200° 
C.  or  2192°  F.,  and  it  expands  slightly  on  passing  from  the  molten  to 
the  solid  state.  It  is  unaffected  by  dry  air,  but  in  a  moist  atmosphere 
it  becomes  coated  with  a  green  carbonate,  malachite,  which  is  also 
found  native  in  most  beautiful  shades,  takes  a  high  polish,  and  is  used 
for  ornamental  articles.  When  heated  or  rubbed  with  much  friction, 
it  emits  a  peculiar,  disagreeable  odor.  In  the  conductivity  of  heat 
(73.6)  and  electricity  (99.95)  it  is  second  only  to  silver  (100). 

Copper  does  not  dissolve  in  acids  with  evolution  of  hydrogen. 

In  nitric  acid  it  dissolves  most  readily,  chiefly  with  the  evolution  of 
nitric  oxide,  forming  copper  nitrate. 

In  sulphuric  acid,  hot  and  concentrated,  it  also  dissolves  readily, 
with  evolution  of  sulphurous  anhydride,  forming  copper  sulphate- 
blue  vitriol. 

In  hydrochloric  acid  copper  is  slowly  soluble. 

Alloys. — The  preparation  of  copper  alloys  is  generally  attended 
with  many  difficulties,  on  account  of  the  high  fusing  point  of  the  metal 
and  the  almost  invariable  presence  of  small  cjuantities  of  other  elements. 

Gold  and  copper  alloy  readily,  the  latter  giving  a  desirable  hardness 
to  gold  and  deepening  its  color.  If,  however,  any  considerable  portion 
of  copper  be  added  to  gold,  the  alloy  is  apt  to  be  brittle,  especially  if 
the  copper  be  not  absolutely  pure.     For  United  States  gold  coins  10 

'  Ganot,  Elements  de  Physique. 


loO     METALS  AND  ALLOYS   USED  IN  PROSTHETIC  DENTISTRY. 

per  cent,  of  ('()])j)er  is  lukled  to  pure  gold,  fj;ivin<^  it  Ji  carat  fineness  of 
21. G  and  a  proper  degree  of  hardness  for  dnrahility. 

Silver  and  copper  also  alloy  readily,  and  the  copper  again  gives  hard- 
ness with  a  slight  change  of  color.  Ten  per  cent,  of  copper  is  added  to 
silver  for  United  States  coin. 

Platinum  and  copper  alloy  at  an  intense  white  heat,  giving  an  alloy 
much  resembling  gold  in  color  and  specific  gravity. 

I^ad  added  to  copper  from  yijoo-to  ^^-^  somewhat  increases  its  duc- 
tility and  malleability,  but  the  presence  of  y-i/fnj  renders  the  metal 
unfit  for  preparation  of  malleable  or  ductile  brass. 

Iron  to  the  amount  of  ywqq  ^^^  ^as  an  injurious  effect  upon  the 
properties  of  copper,  rendering  it  hard  and  brittle. 

Antimony,  bismuth,  and  arsenic  in  small  quantities  have  a  very  in- 
jurious effect  upon  copper. 

Babbitt  metal  consists  of  copper  4,  tin  12,  and  antimony  8,  melted 
separately.  The  antimony  is  added  to  the  tin,  then  the  copper,  and 
12  parts  more  tin   after  fusion. 


Metal. 


Type  Metal — Table  of  Composition.' 

Parts. 


I. 

II. 

III. 

IV. 

V. 

3 

10 

70 

6 

100 

1 

2 

18 

30 

2 

4 

8 

Lead         .... 

Antimonj^ 

Copper     .... 

Bismuth 1  .  .  .  .  2 

Zinc 90 

Tin 10         . .  20 

Nickel 8 

Britannia  Metal  (Wagner's)  consists  of  tin  85.64,  antimony  9.(56, 
copper  0.81,  zinc  3.06,  and  bismuth  0.83. 

Queen's  Metal  consists  of  tin  88.5,  antimony  7.1,  copper  3.5,  and 
zinc  0.9. 

Zinc  alloys  with  copper  in  any  proportion,  all  of  which  alloys  are 
included  in  the  term  brass.  Alloys  of  copper  and  zinc  were  known  in 
the  time  of  Aristotle,  and  the  manufacture  of  brass  was  first  introduced 
in  Germany  in  1550,  but  was  probably  not  produced  by  the  direct 
union  of  the  two  metals  until  1781  in  England,  as  the  art  of  obtaining 
zinc  in  the  metallic  form  became  known  but  a  short  time  previous  to 
that  period.  Notwithstanding  copper  and  zinc  may  be  alloyed  in  any 
proportion,  the  product  is  always  serviceable.  "Generally  speaking, 
it  may  be  said  that  with  an  increase  in  the  percentage  of  copper  the 
color  inclines  more  toward  a  golden,  the  malleability  and  softness  of 
the  alloy  increasing  at  the  same  time.  With  an  increase  in  the  per- 
centage of  zinc,  the  color  becomes  lighter  and  lighter,  and  finally  shades 
into  a  grayish-white,  while  the  alloy  becomes  more  fusible  and  brittle 
and  at  the  same  time  harder."^  Alloys  containing  from  15  to  20  per 
cent,  zinc  are  the  most  ductile.  Those  of  36  to  40  of  zinc  can  be  worked 
cold  as  well  as  hot,  while  those  containing  60  to  70  of  zinc  are  so  brittle 
that  they  cannot  be  worked  at  all.      Raising  this  percentage  to  from  70 

'  Table  from  Brannt.  ^  Brannt,  Metallic  Allois. 


COPPER.  151 

to  90  of  zinc,  the  alloy  again  l)econies  chictile,  and  can  he  worked  quite 
well  when  hot,  but  not  when  cold.  An  alloy  of  copper  75  and  zinc  25 
fuses  at  1750°  F. 

Good  sheet  brass  may  be  made  according  to  many  fonnulic;  two  are 
cited : 

Eosthoru  (Vienna") — Copper  GS.l  and  zine  31.9  parts. 
Eoniilly— Copper  70.1,  zinc  29.26,  lead  0.3S,  and  tin  0.17  parts. 

For  wire,  the  following:"" 

England — Copper  70.29,  zinc  29.26,  lead  0.2S,  and  tin  0.17  parts. 
Neustadt — Copper  71.5  and  zinc  2S.5  parts.'' 

Alloys  containing  as  high  as  37  per  cent,  of  zinc  are  used  as  ductile 
and  malleable  products. 

Fine  cast  brass  usually  contains  from  20  to  50  parts  of  zinc  to  100 
parts  copper,  together  with  lead,  or  tin,  or  both  in  the  proportion  of 
0.25  to  3  per  cent,  of  each.^ 

Oreide  (French  gold)  is  a  brass  allov  much  resembling  gold.  It  takes 
a  fine  polish  and  is  very  ductile,  malleable,  and  much  used  for  the 
manufactiu'e  of  cheap  jewelry,  on  account  of  its  beautiful  color.  Form- 
ula by  analysis. — copper  68.21,  zinc  13.52,  tin  0.48,  and  iron  0.24,' 

"The  most  malleable  of  the  brasses  is  Dutch  metal,  composed  of 
copper  11,  zinc  2  parts;  it  can  be  rolled  out  into  thin  sheets  and  after- 
ward beaten  into  leaves  of  extreme  tenuity,  and  is  used  in  this  form 
for  decorative  purposes  under  the  name  of  Dutch  leaf-gold  or,  reduced 
to  powder  by  levigation  with  a  small  quantity  of  oil  or  honey,  it  is  sold 
as  bronze  powder."^ 

Pinchbeck,  an  alloy  of  copper  88. 8  and  zinc  11.2  parts,  very  much 
resembles  gold;  is  very  ductile  and  malleable;  used  for  cheap  jewelry. 

INIosaic  gold,  a  term  sometimes  applied  to  tin  sulphide,  is  composed 
of  about  equal  parts  of  copper  and  zinc. 

Copper  Coins. — Those  of  the  Ignited  States  are  composed  of  copper 
95,  tin  3,  zinc  2  parts. 

Nickel  and  copper  unite  in  all  proportions,  the  color  varying  from 
the  red  of  copper  to  the  blue-wliite  of  nickel,  according  to  the  propor- 
tions of  the  respective  metals: 

Copper  with  10  per  cent,  of  nickel  gives  a  light  copper-colored  alloy, 
verv  ductile;  with  15,  the  color  is  a  very  pale  red,  but  the  alloy  is  still 
quite  ductile;  with  25,  a  nearly  white  alloy,  and  30,  a  silver-wliite  alloy. 
United  States  nickel  coins  are  composed  of  copper  75  and  nickel  25 
parts. 

Nickel,  copper,  and  zinc  alloys  are  called  German  silver,  argentan,  etc. 
They  are  in  reality  brasses  with  nickel  added,  which  gives  them  a  white 
color  and  much  hardness. 

'  Figures  from  Brannt,  Metallic  Alloys. 
2  Ibid.  3  Ibid. 

*  Kirk,  American  System  of  Dentistry. 


15-2     MI<:TAJ,S  AM)   ALLOYS    USED   /.V  mOSTIIKTir  nFXTfSTnV. 

Tlicse  C'ompDsitioiis  vary  greatly,  as  may  l)e  noticed: 

Copper   .  .  .  .  .  .  .      50  to  0(3  parts. 

Zinc 19  "  30      " 

Nickel 13   "  IS      "« 

White  Metal. — A  variety  of  alloys  consisting  of  copper  and  a  large 
proportion  of  zinc.  They  are  very  white,  or,  tlepending  npon  the  pro- 
portion of  copper,  may  be  a  pale  yellow;  melt  at  a  low  point,  may  be 
cast,  and  are  somewhat  malleable  and  ductile. 

Aluminum  alloys  easily  with  copper,  producing  aluminum  bronze, 
the  alloys  showing  different  properties,  according  to  the  quantity  of 
aluminiun  they  may  contain.  With  00  to  70  per  cent,  aluminum,  a 
very  brittle  alloy  is  produced;  with  50  per  cent.,  one  quite  soft,  but  less 
than  30  per  cent,  of  aluminum,  the  hardness  returns.  The  bronze 
composed  of  copper  95,  aluminum  5,  is  a  beautiful  gold  color,  takes  a 
fine  polish,  casts  well,  is  malleable  hot  or  cold,  and  is  very  strong,  espe- 
cially after  hammering.  With  7.5  per  cent,  aluminum,  the  color  is  a 
greenish  golden.  The  most  common  alloy  is  10  per  cent,  aluminum, 
which  yields  a  bright  golden,  is  not  tarnished  in  air,  may  be  engraved, 
possesses,  it  is  said,  greater  elasticity  than  steel,  and  may  be  soldered 
with  20-carat  gold  solder.    It  melts  at  about  1 700°  F. 

Tin  and  copper  form  a  very  important  series  of  alloys  termed  bronze. 
(See  Tin.) 

Brazier's  Solder. — An  alloy  composed  of  copper,  zinc,  tin,  and  lead 
in  a  variety  of  proportions,  according  to  color  and  fusibility. 

Dr.  Kirk  gives  the  following;  table: 


Copper. 

Zinc. 

Tin. 

Lead. 

A. 

Golden  yellow 

.      53.50 

43.34 

2.12 

B. 

Medium  liglit 

.     43.75 

.50.5.S 

3.75 

1 

C. 

White 

.      57.50 

27.90 

14.90 

trace 

It  is  used  in  soldering  brass  and  copper,  which  may  also  be  soldered 
with  the  ordinary  soft  solder,  spelter  (zinc),  or  silver  solder. 

Copper  is  a  constituent  of  most  hard  solders,  its  proportion  varying 
according  to  the  purpose  for  which  they  are  to  be  used.  (See  Silver 
and  Gold.) 


ZINC. 

Zincum.  Symbol,  Zn. 

Atomic  weight,  64.9.  Malleability,  eighth  rank 

Melting  point,  415°  (779°  F.).  Tenacity,  sixth  rank. 

Ductility,  sixth  rank.  Specific  gravity,  6.915. 

Conductivity  (heat).  Conductivity  (electricity). 

(Silver  being  100). 

'  Brannt,  Metallic  .\lloys. 


ZISC.  1 53 

Occurrence. — Zinc  is  a  somewhat  abundant  metal,  but  never  occurs 
in  the  nati\e  state.  It  is  found  as  a  carbonate,  sulphide,  silicate,  etc., 
associated  with  lead  ores  in  many  districts ;  large  supplies  are  obtained 
from  Silesia  and  from  the  neighborhood  of  Aachen. 

Properties. — Zinc  is  a  bluish-white  metal,  which  but  slowly  tar- 
nishes in  moist  air,  usually  forming  a  superficial  carbonate;  it  has  a 
specific  gravity  of  6.915,  and  is,  under  ordinary  circumstances,  quite 
brittle,  but  when  heated  to  100°  or  150°  C.  it  may  be  rolled  or  ham- 
mered into  thin  sheets,  or  drawn  into  wire;  and,  what  is  very  remarka- 
ble after  such  treatment,  it  retains  its  malleability  when  cold;  the  sheet 
zinc  of  commerce  is  thus  made.  If  the  temperature  be  carried  to  205° 
C.  it  again  becomes  so  brittle  that  it  may  be  easily  powdered  in  a  mor- 
tar. Care  should  be  exercised  in  handling  hot  zinc  dies,  for  if  by  acci- 
dent one  be  dropped  upon  a  hard  surface  it  is  likely  to  be  ruined.  The 
metal  melts  at  415°  C.  or  779°  F.  It  boils  and  volatihzes  at  1040°  C.  or 
1904°  F.,  and,  if  air  be  admitted,  bums  with  a  splendid  greenish  incan- 
descence, forming  the  oxide.  In  boiling  water  zinc  is  said  to  be  attacked 
appreciably ,  forming  the  hydroxide,  Zn2HO,  with  evolution  of  hydrogen. 

Zinc  has  long  been  very  extensively  used  in  the  dental  laboratory 
for  making  dies.  Its  comparatively  low  fusibility,  hardness,  and  other 
properties  eminently  fit  it  for  this  purpose. 

Pure  zinc  dissoh  cs  very  slowly  in  acids  (or  alkalis),  unless  in  contact 
with  copper,  platinum,  or  some  less  positive  metal.  Any  metallic 
impurity  in  zinc  renders  it  quite  soluble  in  the  acids  or  alkalis. 

Alloys. — Zinc  readily  unites  with  gold.  The  malleability,  brilliancy, 
and  color  of  gold  are  impaired  by  a  content  of  zinc. 

Small  pieces  of  platinum  may  be  dissolved  in  molten  zinc,  and  the 
union  is  attended  with  considerable  energy,  owing  to  the  formation 
of  a  definite  chemical  compound.  The  alloy  is  hard  and  brittle.  An 
alloy  may  be  prepared  of  platinum,  16;  copper,  7;  and  zinc,  1;  which 
very  much  resembles  gold  in  color,  specific  gravity,  and  ductility. 

Silver  and  zinc  have  a  great  affinity  for  each  other.  This  fact,  with 
the  knowledge  that  zinc  and  lead  are  comparatively  so  incompatible, 
led  to  the  process  of  desilvering  lead  by  the  assistance  of  zinc.  The 
alloy  of  silver  and  zinc  is  best  obtained  by  throwing  the  required  quan- 
tity of  zinc  wrapped  in  paper  into  molten  silver,  stirring  thoroughly 
with  an  iron  rod,  and  pouring  the  fused  mass  at  once.  The  alloy  of 
two  parts  zinc  and  one  part  silver  is  flexible,  ductile,  and  has  nearly 
the  color  of  pure  silver.  Larger  proportions  of  zinc  produce  brittle 
alloys. 

Iron  plate  and  ware  when  perfectly  cleaned  may  be  immersed  in 
molten  zinc  and  the  sm^ace  alloyed  slightly,  forming  what  is  known 
as  "galvanized  iron,"  the  name  being  derived  from  the  circumstance 
that  the  coating  is  analogous  to  that  produced  by  electric  means. 
Zinc  alloys  \vith  the  iron  melting  pots  of  the  laboratory,  the  admLxture 
rendering  the  zinc  less  fluid  when  molten  and  more  difficult  to  fuse. 
This  contamination  may  be  prevented  by  coating  the  pot  with  whiting. 

^Yith  lead  zinc  does  not  alloy,  except  to  a  very  slight  degree.    "Mat- 


154     METALS  AND   ALfJ/YS    CsKD   fN  PROSTUETIC  DENTrSTRV. 

tliiesseii  found'  that  on  incltiiiff  ('(|iial  ])art.s  of  zinc  and  U-ad,  and,  after 
well  mixini;,  allowing  the  alloy  to  eool  slowly,  they  separate,  but  the 
heavier  lead  on  subsidini^  retains  l.O  per  cent,  of  the  zinc  alloyed  with 
it;  while  on  the  other  hand  the  uj)per  layer  of  zinc  thrown  out  retains 
1.2  per  cent,  of  lead." 

It  often  occurs  that  lead  and  zinc  will  become  mixed  in  the  laboratory, 
and  is  seldom  discovered  until  the  molten  mixture  is  poured.  Then 
the  lead,  owing  to  its  greater  specific  gravity,  falls  to  the  bottom  of  the 
mold,  forming  the  alveolar  ridge  of  the  die,  rendering  it  worthless. 
Many  times  the  counter-die  is  poured  before  the  mistake  is  noticed, 
resultins:  in  a  union  of  the  die  and  counter-die. 

Tin  and  zinc  alloy  in  almost  any  proportion.  Mr.  Fletcher  recom- 
mends an  alloy  of  zinc  2  parts  and  tin  1  part  for  making  dies  for  swag- 
ing, claiming  the  impression  from  the  sand  is  much  finer,  and  the 
shrinkage  on  cooling  is  greatly  reduced.  It  melts  much  lower  than 
zinc  alone,  hence  some  care  must  be  exercised  in  pouring  the  counter- 
die.  The  die  should  be  perfectly  cold  and  the  lead  should  be  just  hot 
enough  to  pour,  but  not  sufficiently  heated  to  char  a  slip  of  paper. 


BISMUTH. 

Symbol,  Bi. 
Atomic  weight,  206.9.  Malleability,  brittle. 

Melting  point,  264°  (507°  F.)  Tenacity,  brittle. 

Ductility,  brittle.  Specific  gravity  9.823. 

Conductivity  (heat),  1.8.  Conductivity  (electricity),  1.24. 

(Silver  being  100.) 

Occurrence. — Practically  the  only  ore  of  this  element  is  the  native 
metal  found  disseminated  in  veins  through  slate  rock  associated  with 
the  ores  of  copper,  iron,  cobalt,  nickel,  silver,  gold,  and  arsenic. 

Properties. — Bismuth  is  a  highly  crystalline,  iT^rd,  and  very  brittle 
metal,  having  a  grayish-white  color,  with  a  decided  reddish  tint.  Its 
specific  gravity  is  9.823,  and  it  fuses  at  264°  (507.2°  F.).  It  expands 
about  3^  of  its  volume  upon  cooling,  and  imparts  this  property  to 
its  alloys.  The  metal  volatilizes  at  a  high  temperature,  and  has  a 
specific  heat  of  0.0308.  It  is  the  most  diamagnetic  of  all  substances. 
Exposed  to  the  air  at  ordinary  temperatures,  it  is  unaffected,  but  when 
heated  to  a  red  heat  it  rapidly  oxidizes,  producing  a  beautiful  play  of 
colors. 

Sulphuric  and  hydrochloric  acids  have  but  slight  action  on  bismuth, 
while  nitric  acid  dissolves  it  very  energetically. 

Alloys. — Bismuth  has  its  greatest  use  in  the  preparation  of  low 
fusing  alloys. 

With  tin  bismuth  alloys  in  any  proportion.  A  very  small  quantity 
of  the  metal  imparts  to  tin  more  hardness,  sonorousness,  lustre,  and  a 
fusibility  lower  than  either  of  the  metals  taken  separately  possesses. 
An  alloy  of  equal  parts  of  the  two  metals  fuses  at  212°  C. 

'  Makins'  Metallurgy,  p.  62. 


Bi. 

Sb. 

Sn. 

Pb. 

9.0 

10.5 
Type-metal. 

48.0 

32.5 

8.0 

1.0 

4.0 

5.0 

1.0 

3.0 

8.0 

BISMUTH.  155 

With  k'lul  bismutli  alloys  very  easily,  producino-  an  alloy  which  is 
inalleahle  if  the  proportion  of  bismuth  does  not  exceed  that  of  lead. 
The  specific  gravity  is  greater  than  the  mean  of  the  two  taken  separately. 
Its  alloys  are  whit(>,  lustrous,  harder  than  lead,  and  more  malleable 
up  to  a  certain  proportion.  Bismutli  1  and  lead  2  gives  a  very  ductile 
and  malleable  alloy  fusing  at  330°  F. 

With  antimony  it  produces  a  grayish,  brittle,  lamellar  alloy.  Lead 
and  tin  added  render  it  malleable,  l3ut  its  fusibility  is  increased  rather 
than  decreased.  Such  alloys  are  very  frequent  and  much  used  in  the 
preparation  of  Britannia  and  Queen's  metal. 


Cliche-metal 


Alloys  of  bismuth,  tin,  and  lead  are  known  as  the  triple  alloys,  and 
are  very  numerous  and  useful. 

Newton's  alloy,  sometimes  called  "Melotte's  metal,"  consists  of 
bismuth  8,  lead  5,  and  tin  3  parts,  and  fuses  at  202°  F. 

Rose's  fusible  alloy  is  composed  of 


Bismuth         .  .  -        . 

Tin 

Lead     ...... 

The  first  fuses  at  200.75°  F.  and  the  second  at  174.2°  F.^  They  w^ere 
used  as  safety  plates  and  inserted  in  the  top  of  steam  boilers,  intended 
to  prevent  the  explosion  of  boilers  by  allowing  the  steam  to  escape  at 
a  certain  tension. 

Wood's  metal  consists  of  lead  4,  tin  2,  bismuth  5  to  8  and  cadmium 
1  to  2,  melts  at  140°  to  161.5°  F.,  in  color  resembles  platinum,  and  is, 
to  a  certain  extent,  malleable.^ 

Onion's  fusible  alloy  contains  lead  3,  tin  2,  and  bismuth  5  parts,  and 
melts  at  197°  F. 

La  Nation  describes  a  new  fusible  alloy,  of  which  the  follownng 
is  the  formula:  Bismuth  48,  cadmium  13,  lead  19,  and  tin  26.  It  melts 
at  158°  C.  and  resists  great  pressure.    • 

Hodgen's  fusible,  alloy,  for  making  dies  and  counter-dies  by  the  dipping 
process,  is  composed  of  the  following:  Bismuth  8,  lead  5,  tin  3,  and 
antimony  2.  It  is  a  light,  lustrous  alloy,  very  hard,  slightly  malleable, 
expands  slightly  on  cooling,  copying  the  finest  of  lines,  takes  a  high 
polish,  and  resists  great  pressure,  melting  at  224°  F, 

Dr.  Mathews'  Fusible  Alloy. — This  alloy  is  composed  of  bismuth  48, 
cadmium  13,  and  tin  19  parts.  It  melts  below  the  boiling  point  of 
water  and  may  be  packed  with  the  fingers.  It  may  be  poured  into 
plaster  impressions  immediately  after  they  have  been  taken,  producing 

1  WilUam  T.  Brannt.  "  Ibid. 


I. 

II. 

2 

8  parts. 

1 

3      " 

1 

8      " 

Bismuth. 

Tin. 

Lead. 

7 

4 

2 

16 

7 

4 

8 

2 

6 

156     METALS  AM)   ALLOYS    USED   IN  I'llOSTIIETIC  DEM'ISTRY. 

.sharj),  bright,  hard  dit'.s,  with  which  .sliot  niav  1)0  ii.sed  for  the  counter- 
die. 

Darcet's  fusible  alloys  are  a  series  of  proportions  of  bismuth,  tin,  and 
lead,  and  their  melting  ])oint  varies  a,s  per  the  following  table: 

Parts. 

Melts. 

.  212°  F. 
.  212°  F. 
.      205°  F. 

Most  of  these  fusible  alloys  are  of  much  value  in  the  dental  laboratory 
m  the  hands  of  a  practical,  resourceful  man.  'J'he  cleaner  ones  may 
when  lack  of  time  will  not  permit  of  a  more  perfect  repair,  be  used  to 
mend  a  denture  or  replace  a  tooth  or  block  of  teeth  on  a  vulcanite  plate, 
and  the  more  fusible  ones  may  be  used  for  the  same  purpose,  even 
though  the  base  be  celluloid.  In  replacing  teeth  undercuts  may  be 
made  with  a  file,  or  preferably  with  a  large  bur  in  the  engine,  the  tooth 
placed  in  position,  and  the  alloy  packed  in  with  warm  instruments, 
smoothed,  and  afterward  polished.  These  alloys  are  also  valuable 
baths  for  tempering  steel  instruments.  They  give  a  very  exact  temper- 
ature, which  may  be  adjusted  to  the  purpose  intended.  They  are  used, 
according  to  Thurston,  by  placing  the  articles  on  the  surface  of  the 
unmelted  alloy  and  gradually  heating  until  fusion  occurs  and  they 
fall  below  the  surface,  at  which  moment  their  temperature  is  right; 
they  are  quickly  removed  and  cooled  in  water. 


TIN. 

Stannum.  Symbol,  Sn. 

Atomic  weight,  118.1  Malleability,  fourth  rank. 

Melting  point,  228°  (442°  F.).  Tenacity,  .seventh  rank. 

Ductility,  seventh  rank.  Specific  gravity,  7.29. 

Conductivity  (heat)  14.5.  Conductivity  (electricity),  12.36. 

(Silver  being  ino.) 

Occurrence. — Tin  occurs  chiefly  as  tinstone,  cassiterite,  or  native 
oxide,  SnOj.  The  pure  ore  is  colorless  and  very  scarce.  Another  native 
form  known  as  "wood  tin"  occurs  in  roundisli  masses.  The  metal  is 
rarely,  if  ever,  found  fi-ee. 

Properties. — Pure  tin  is  white  (except  for  a  slight  tinge  of  blue);  it 
exhibits  considerable  lustre,  and  Is  not  subject  to  tarnishing  on  expo- 
sure to  normal  air.  It  is  soft  and  exceedingly  malleable;  indeed,  it  is 
said  it  may  be  beaten  into  foil  -^-^  of  a  mm.  in  thickness;  at  100°  C. 
it  may  be  drawn  into  wire,  but  is  almost  devoid  of  tenacity.  That  it 
is  elastic,  within  narrow  limits,  is  proven  by  its  clear  ring  when  struck 
with  a  hard  body  under  circumstances  permitting  free  vibration. 
Though  it  is  seemingly  amorphous  it  has  a  crystalline  structure,  hence 
the  crackling  noise  known  as  the  "tin  cry"  which  a  l)ar  of  tin  emits 
on  being  bent.      The  crystalline  structure  must  also  account  for  the 


TIN.  157 

strange  fact  that  an  ingot,  when  exposed  to  the  temperature  of  — .'iO° 
C.  for  a  siiffieient  length  of  time,  becomes  so  l)rittle  that  it  falls  into 
powder  under  pesde  or  luimmer.  At  some  temperature  near  its  fusing 
point  it  again  becomes  brittle.  Tin  fuses  at  228°  (442.4°  F.).^  At  a 
red  heat  it  begins  to  volatilize  slowly;  at  1600°  to  1808°  C.  it  boils^ 
and  may  be  distilled.  Tlie  hot  vapor  jjroduced  combines  with  the  oxy- 
gen of  the  air,  forming  the  white  oxide,  SnOj.  The  specific  gravity 
is  7.29.     Its  specific  heat  is  0.0562. 

Casts  of  tin  are  used  to  vulcanize  upon,  and  plaster  casts  are  often 
covered  with  tin-foil  to  give  a  clear  and  finished  appearance  to  the 
denture  after  the  process  of  vulcanization. 

Tin  dioxide  under  the  name  of  "polishing  putty"  is  used  for  polish- 
ing glass,  ground  porcelain  surfaces,  hard  metals,  and  similar  sub- 
stances. 

The  three  mineral  acids  and  boiling  solutions  of  the  caustic  alkalis 
act  on  tin. 

Alloys. — Gold  and  tin  form  a  malleable  alloy,  provided  the  tin  be 
pure  and  does  not  exceed  in  quantity  10  per  cent. 

Platinum  and  tin  in  equal  proportions  form  a  hard,  but  brittle,  alloy, 
fusing  at  a  comparatively  low  temperature. 

Palladium,  says  Mr.  Makins,  forms  a  very  brittle  alloy  with  tin. 

In  view  of  the  fact  that  gold,  platinum,  and  palladium  so  readily 
unite  with  tin  to  form  alloys  whose  fusing  points  are  so  comparatively 
low,  and  in  view  of  the  behavior  of  tin  with  other  metals,  and  of  metals 
in  general  toward  each  other,  there  is  little  reason  to  doubt  a  chemical 
affinity  of  tin  for  these  metals.  The  affinity  of  tin  for  gold  in  particular 
has  been  clearly  demonstrated  by  Dr.  Matthiessen.  Into  a  crucible 
of  molten  tin  a  rod  of  gold  and  one  of  copper  were  dipped,  the  latter 
having  been  previously  tinned  to  ensure  perfect  contact.  The  gold 
united  readily  and  rapidly  with  the  tin,  while  the  copper  rod  remained 
unaffected.  A  gold  wire  which  has  been  superficially  tinned  will  melt 
like  one  of  tin  when  held  in  the  flame  of  a  Bunsen  burner.  A  wire  of 
tinned  copper  exposed  to  the  same  heat,  under  like  circumstances, 
remains  unaffected,  except  that  the  tin  is  burned  off.  The  affinity  of 
tin  for  platinum  is  so  great,  states  Clarke,  that  if  tin  and  platinum 
foils  be  rolled  together  and  heated  before  the  blowpipe,  combination 
takes  place  explosively.  The  affinity  of  tin  for  gold  is  uncpiestionably 
an  interesting  subject  for  the  dentist,  in  view  of  the  place  these  two 
metals  occupy  in  operative  dentistry. 

Silver  alloys  with  tin,  and,  in  the  proportion  of  80  of  the  former  to 
20  of  the  latter,  it  is  said  produces  a  very  tough  alloy. 

Dr.  G.  F.  Reese's  alloy  for  artificial  dentures,  constructed  by  the  cheo- 
plastic  process,  is  composed  of  tin  20,  gold  1,  and  silver  2  parts.  Other 
alloys  much  used  in  cheoplastic  work  are  composed  largely  of  tin. 

Bean's  alloy,  intended  for  casting  lower  dentures,  is  composed  of  tin 
95  and  silver  5  parts. 

Antimony  1  and  tin  16  parts  form  another  alloy,  which  is  intended 

1  Rudberg.  ^  Williams. 


158     METALS  AND  ALLOYS  USED  IN  PROSTHETIC  DENTISTRY. 

for  the  same  purpose,  and  was  introduced  by  the  hite  Dr.  William  li. 
Kiufjshury. 

Britannia  metal  is  made  under  a  great  variety  of  fc^rmuhe;  one  known 
as  English  is  composed  of  antimony  7.8,  tin  90.7,  and  copper  1.5.  It 
sometimes  contains  lead  or  bismuth. 

Tin  is  easily  deposited  upon  small  articles  of  brass  or  copper  by 
simple  immersion,  as  by  the  following  experiment: 

Place  the  articles  in  layers  between  sheets  of  grain  tin  in  a  saturated 
solution  of  potassium  })itartrate  and  boil.  A  little  stannous  chloride 
may  also  be  added,  if  necessary. 


LEAD. 

Plumbum.  Symbol,  Pb. 

Atomic  weight,  205.35.  Malleability,  seventh  rank. 

Melting  point,  325°  (617°  F.)  Tenacity,  Jowest  (eighth)  r-ink. 

Ductility,  eighth  rank.  Specific  gravity,  11.25. 

Conductivity  (heat),  8.5.  Conductivity  (electricit}-),  8.32. 

(Silver  being  100.) 

Occurrence. — This  abundant  and  very  useful  metal  Ls  almost  wholly 
obtained  from  its  native  sulphide  (PbS),  or  galena,  and  is  rarely,  if 
ever,  found  free. 

AMien  found  associated  with  silver,  the  ore  is  termed  argentiferous 
galena. 

Properties. — Pure  lead  is  a  feebly  lustrous,  bluish-white  metal, 
endowed  with  a  high  degree  of  softness  and  plasticity,  and  almost 
entirely  devoid  of  elasticity.  A  wire  j^  of  an  inch  in  thickness  is 
ruptured  by  a  weight  of  about  thirty  pounds.  It  is  said  to  he  the  least 
tenacious  of  all  metaLs  in  common  use.  Its  specific  gravity  is  about 
11.25.  It  melts  at  325°  C.  or  617°  F.  At  a  bright-red  heat  it  vaporizes 
and  at  a  white  heat  boils.  Its  specific  heat  is  0.0314.  Lead  exposed  to 
ordinary  air  is  rapidly  tarnished,  forming  it  is  supposed  a  suboxide. 
The  same  supposed  suboxide  is  formed  upon  lead  kept  in  a  state  of 
fasion  in  the  presence  of  air,  when  at  the  same  time  the  metal  rapidly 
absorbs  oxygen;  then  the  monoxide  (PbO)  is  formed,  the  rate  of  oxid- 
ation increasing  with  the  temperature.  Its  chief  use  in  dentistry  is  in 
the  laboratory  as  a  counter  die. 

Action  of  Acids  on  Lead.— The  presence  of  carbonic  acid  in  a  water 
does  not  affect  its  action  on  lead.  Aqueous  non-oxidizing  acids  gener- 
ally have  little  or  no  action  on  lead  in  the  absence  of  air. 

Sulphuric  acid,  when  dilute  (20  per  cent,  solution  or  less),  has  no 
action  on  lead,  even  when  air  is  present,  nor  upon  boiling.  Stronger 
acid  does  act  slowly,  in  general,  but  appreciably,  the  more  so  the  greater 
its  concentration  and  the  higher  its  temperature.  Pure  lead  is  more 
readily  acted  upon  than  that  contaminated  with  antimony  or  copper. 
Boiling  concentrated  sulphuric  acid  converts  lead  into  the  sulphate, 
with  evolution  of  sulphurous  oxide. 


LEAD.  159 

The  mrtal  is  readily  dissolved  in  dilute  nitric  acid,  nitrogen  dioxide 
being  evolved  and  plumbic  nitrate  formed. 

Strong  and  hot  hydrochloric  acts  but  slowly  upon  lead,  forming  the 
dichloride  and  liberating  hydrogen. 

Water  when  pure,  has  no  action  on  lead  per  se.  In  the  presence  of 
free  oxygen  (air),  however,  the  lead  is  quickly  attacked,  forming  a 
hydrated  oxide,  Pb2HO  =  PbOH20,  which  is  appreciably  soluble  in 
water,  rendering  the  liquid  alkaline.  When  carbonic  acid  is  present 
the  dissolved  oxide  is  soon  precipitated  as  basic  carbonate — PbCOg 
(which  is  slightly  soluble  in  water  containing  carbon  dioxide) — so 
there  is  room  made,  so  to  say,  for  fresh  hydrated  oxide,  and  the  corrosion 
of  lead  progresses.  Now,  all  soluble  lead  compounds  are  strongly 
cumulative  poisons,  hence  the  danger  involved  in  using  lead  pipes  or 
cisterns  in  the  distribution  of  pure  waters.  We  emphasize  the  word 
"pure,"  because  experience  shows  that  the  presence  in  water  of  even 
small  proportions  of  bicarbonate  or  sulphate  of  lime  prevents  its  action 
on  lead.  This  little  sulphate,  almost  invariably  present,  causes  the 
deposition  of  a  very  thin  but  closely  adherent  film  of  lead  sulphate  upon 
the  surface  of  the  metal,  which  protects  it  from  further  action. 

Alloys. — Pure  lead  unites  with  almost  all  metals.  Very  small  quan- 
tities of  lead  admixed  with  the  noble  metals  destroy  completely  their 
malleability,  and  hence  render  them  unworkable.  It  is  said  that 
YWTo  P^rt  of  lead  in  gold  will  greatly  impair  its  coining  property,  and 
that  gold  containing  g-jy-Q  part  of  lead  is  "rendered  unfit  for  coinage." 
The  gold  drawer  in  the  dental  laboratory  is  often  so  situated  that  it  is 
almost  impossible  to  prevent  particles  of  lead  from  accumulating  with 
the  gold  scraps  and  filings.  These,  however,  may  be  easily  removed 
by  roasting  with  potassium  nitrate  and  sulphur.^ 

Tin  unites  with  lead  in  almost  any  proportion  with  slight  expansion.^ 

The  following  table  gives  an  idea  of  the  melting  points  of  alloys  of 
lead  and  tin: 

An  alloy  of — 

Lead  1,  Tin  2  . 

"     1,     "   6  . 

"     2,     "    1  . 

"     4,     "    1  . 

".  17,     "    1  . 

With  tin  1  part  and  lead  5  parts^  Dr.  Haskell  makes  counter-dies  to 
be  used  with  Babbitt-metal  dies.  It  fuses  at  a  lower  temperature  than 
the  die  alloy,  and  also  has  the  advantage  of  being  harder  than  lead, 
which  he  claims  is  too  soft  for  counter-dies. 

Tin-lead  alloys  are  used  largely  in  soldering.  The  following  are 
compositions   and  melting  points  of  frequently  used  compounds:* 

Grade.  Tin.  Lead.  Melts  at— 

Fine      solder  ....     2  1  340°  F. 

Common  "  .  .  .  .1  1  370°  F. 

Coarse       "  .  .  .  .1  2  442°  F. 

>  See  Gold.  ^  Kuppfer. 

3  The  author  has  found  the  fusing  point  of  this  alloy  to  be  378°  F.  *  Tomlinson. 


Fuses  at — 

.      340° 

F. 

.      382° 

F. 

.      442° 

F. 

.      498° 

F. 

.      557° 

F 

IGO     MFA'ALS  AND  ALLOYS   USED  IN  PROSTHETIC  DENTISTRY. 

Pewter  may  be  said  to  be  substantially  an  alloy  of  the  same  two 
metals;  but  small  (|uantities  of  copper,  antimony,  and  zinc  are  fre- 
([uently  added.  Common  pewter  contains  about  5  parts  of  tin  for 
1  of  lead.  In  France  a  tin-lead  alloy,  containing  not  over  18  per  cent, 
of  lead,  is  recognized  by  law  a,s  being  fit  for  measures  for  wine  or  vinegar. 
"Best  pewter"  is  simply  tin  alloyed  with  a  mere  trifle  {\  per  cent,  or 
less)  of  copper. 

liCad  contaminated  with  small  proportions  of  antimony  is  more 
highly  ])roof  against  vitriol  than  the  pure  metal.  An  alloy  of  S3  parts 
of  lead  and  17  parts  of  antimony  is  used  as  type  metal;  other  propor- 
tions are  used,  however,  and  other  metals  added  besides  antimony — 
e.  g.,  tin,  bismuth — to  give  the  alloy  certain  properties. 

Arsenic  renders  lead  harder.  An  alloy  made  by  the  addition  of 
about  Jg-  of  arsenic  is  used  for  making  shot. 

Lead  forms  a  very  important  part  in  "  fusible  alloys."^ 

'  See  Bismuth. 


CHAPTER    III 

PORCELAIN  TEETH. 

By  Charles  J.  Essig,  M.D.,  D.D.S. 

Revised  by  Ellison  Hillyer,  D.D.S. 

The  general  use  of  porcelain  teeth  in  dentistry  began  about  1825. 
Previous  to  that  date  the  materials  and  means  employed  in  the  con- 
struction of  artificial  dentures  were  confined  to  the  various  methods  of 
setting  human  teeth,  the  teeth  of  animals,  and  carving  dentures  of  hip- 
popotamus tusks,  walrus,  and  elephant  ivory,  etc.  The  part  of  the 
human  tooth  used  by  the  dentists,  except  in  transplantation,  was  the 
crown  portion. 

MATERIALS    USED    IN   THE    FORMATION    OF   BODIES   AND 

ENAMELS. 

These  are  feldspar,  silica,  and  kaolin  or  clay.  The  pigments  employed 
to  imitate  the  various  shades  of  color  of  the  natural  enamel,  dentin,  and 
gums  are  titanium  oxide,  platinum,  cobalt,  iron,  gold,  and  tin. 

The  Body. — ^The  body  represents  the  dentin  of  the  natural  tooth,  and 
is  composed  of  feldspar,  silica  (in  the  form  of  finely  ground  quartz),  and 
kaolin  (clay),  and  the  yellow-white  or  ivory-like  color  of  that  portion  of 
a  tooth  is  imparted  to  it  by  the  addition  of  finely  ground  titanium  oxide. 

The  Frits. — A  frit  is  an  imperfectly  vitrified  mass,  formed  by  the  partial 
fusion  of  sand  and  fluxes,  from  which  glass  is  made  by  melting.  The 
frits  which  enter  into  the  composition  of  teeth  are  crude  colors  composed 
of  metallic  oxides,  such  as  those  of  gold,  tin,  cobalt,  etc.,  ground  exceed- 
ingly fine,  in  combination  with  feldspar  and  certain  fluxes,  which  will 
hereafter  be  described.  These  are  burned  in  a  suitable  crucible,  and 
then  powdered  for  use  in  imparting  tints  to  enamels. 

Enamels. — Enamels  are  composed  chiefly  of  feldspar,  to  which  is  added 
sufficient  quantities  of  the  different  frits  to  produce  as  nearly  as  possible 
the  colors  of  the  natural  teeth  and  gums. 

Bodies  and  enamels  especially  prepared  for  the  manufacture  of  por- 
celain teeth  should  possess,  after  burning,  translucency  and  natural 
color,  together  with  strength  and  heat-conducting  qualities  to  a  degree 
that  will  admit  of  soldering  without  danger  of  fracture  from  unequal 
expansion.  Translucency  and  the  power  of  withstanding  high  tem- 
perature in  soldering  depend  largely  on  the  feldspar,  which  forms  four- 
fifths  of  the  bulk  of  the  body. 

Silica  is  next  in  importance  as  a  constituent  of  the  body :  its  function 
is  to  add  density  and  the  strength  required  for  masticatory  purposes, 
and,  being  highly  infusible,  to  assist  in  retaining  the  teeth  in  shape  dur- 
ing the  burning  process.     Without  silica  the  teeth  when  near  the  fusing 

11  161 


362  POliCKLAiy   TKKTII. 

point  woukl  evince  a  tendency  to  a.ssunie  tlic  .s])lierical  form,  and  their 
lines  and  characteristic  features  would  l)e  lost. 

Kaolin,  according  to  S.  Welles  Williams,  "  Middle  Kingdom,"  ol)- 
tained  its  name  from  Kao  Ling,  a])lace  in  China  where  it  was  first  ob- 
tained. The  name  has  been  ado])te(l  for  all  varieties  of  fel(ls])athic  com- 
ponents of  porcelain.  Kaolin  and  the  clays  in  general  give  plasticity  to 
the  body,  by  which  the  workman  is  enabled  to  mold  and  handle  the 
unburned  teeth  and  blocks  without  danger  of  breaking  them;  it  also 
imparts  strength  to  the  porcelain  mixture. 

Feldspar. — This  is  generally  spoken  of  as  a  double  silicate  of  alu- 
minum and  potassium,  and  is  represented  by  the  formula  A1/)3.K2(), 
.GSiO,.  The  best  quality  of  feldspar  is  found  in  the  neighborhood  of 
Wilmington,  Del.  It  possesses  a  distinct  cleavage,  and  when  broken 
splits  into  plates  of  more  or  less  magnitude.  It  is  of  an  indefinite  color, 
between  yellow  and  pink,  but  when  fused  in  the  furnace  it  becomes 
transparent  and  colorless,  and  if  not  exposed  to  a  too  prolonged  or  an 
excessively  high  temperature  it  retains  its  original  form  without  round- 
ing at  the  corners :  this  is  one  of  the  tests  of  good  feldspar. 

Feldspar  from  different  parts  of  the  same  quarry  has  been  observed 
to  differ  in  quality.  In  selecting  spar  for  the  preparations  of  enamel  a 
number  of  pieces  broken  from  the  most  perfect-appearing  specimens 
should  be  fused  in  the  furnace  to  determine  the  quality.  The  crude 
pieces  from  which  the  samples  were  taken,  if  found  satisfactory,  are  then 
broken  into  small  fragments  with  a  steel  hammer  until  they  become  of  a 
size  to  admit  of  its  being  ground  in  a  large  Wedgwood  mortar;  at  intervals 
the  powder  is  sifted  through  a  No.  10  bolting-cloth  sieve,  placed  iix 
covered  jars,  and  kept  dry  for  future  use. 

In  the  preparation  of  feldspar  for  enamels  the  grinding  should  not  be 
carried  too  far,  as  transparency  may  be  greatly  lessened,  or  even  entirely 
lost,  by  its  being  ground  too  fine.  The  effect  of  a  complete  obliteration 
of  the  crystallization  of  the  feldspar  by  too  much  grinding  may  be  ob- 
served in  a  test  suggested  by  Dr.  William  R.  Hall  in  the  chapter  on 
"^Moulding  and  Carving  Porcelain  Teeth,"  American  System  of  Dentis- 
try: It  consists  in  placing  on  a  slide  covered  with  coarse  silex  a  small 
piece  of  crude  feldspar  of  the  best  cjuality;  then  taking  another  piece  from 
the  same  specimen,  grinding  it  very  fine,  and  fusing  the  two  in  the 
furnace;  when  cold  the  difference  in  appearance  will  demonstrate 
that  when  ground  into  a  very  fine  powder  loss  of  transparency  is  appa- 
rent, and  that  to  preserve  its  beauty  feldspar  must  be  ground  only  to  a 
certain  fineness,  beyond  which  opacity  is  the  result. 

In  preparing  feldspar  in  large  cpiantities  for  extensive  use  by  the 
manufacturers  of  molded  teeth  it  is  customary  to  calcine  the  spar  by 
heating  to  redness  and  dropping  it  into  water  while  hot.  This  is  done 
to  facilitate  the  reduction  of  the  large  masses  into  small  fragments  suit- 
able for  grinding  in  the  mortar,  which  in  the  large  factories  consists  of  a 
tub  with  a  burr-stone  or  quartz  bottom.  The  pestle,  which  is  generally 
formed  of  a  piece  of  the  same  mineral,  is  arranged  to  revolve  by  machin- 
ery. The  grinding  is  done  under  water.  While  this  plan  is  less  laborious 
than  dry  grinding,  it  probably  never  affords  as  good  results,  in  conse- 
quence of  the  excessive  fineness  of  the  powdered  spar. 


MATERIALS   USED.  163 

Silica  (Si(\,).— This  body,  sometimes  called  ,c[uartz,  occurs  in  crystal- 
line and  amorphons  forms;  it  is  colorless,  infusible  at  ordinary  tempera- 
tures, insoluble  in  water  and  in  all  the  acids  excej)t  hydrofluoric.  The 
amorphous  and  gelatinous  varieties  are  partially  soluble  in  alkaline  car- 
bonates, but  quite  soluble  in  caustic  alkalies.  Silica  combines  with  the 
bases  to  form  silicates. 

A  variety  of  cjuartz  well  suited  for  use  in  the  manufacture  of  porce- 
lain teeth  is  found  in  great  abundance  in  Pennsylvania  and  other  parts 
of  the  United  States.  It  occurs  in  large  irregular  masses,  white  in  color, 
and  very  difficult  to  powder.  It  is  used  for  the  purpose  of  giving  sta-  ' 
bility  and  firmness  to  porcelains,  and  its  infusibility  stiffens  and  keeps 
the  other  materials  in  shape,  so  that  an  object  made  of  porcelain  may 
preserve  its  molded  form  while  exposed  to  the  high  temperature  dur- 
ing the  fusing  process.  For  these  reasons  it  is  incorporated  with  feld- 
spar and  clay,  and  is  looked  upon  as  the  "main  prop  in  tooth  body,"  in 
which  it  is  just  as  essential  for  the  purpose  of  lessening  fusibility  as  flux 
is  essential  in  enamels,  which  are  required  to  fuse  more  readily. 

Quartz  must  be  ground  under  water  to  an  impalpable  powder.  The 
proper  degree  of  fineness  may  be  ascertained  by  placing  a  small  portion 
of  the  powdered  quartz  on  the  end  of  the  tongue:  if  it  is  found  to  be 
without  grittiness  when  rubbed  against  the  teeth,  it  may  be  dried  for  use. 

The  preliminary  steps  in  the  reduction  of  this  hard  mineral  to  a  fine 
state  of  division  consist  in  heating  to  a  bright  redness  as  large  pieces  as 
the  muffle  of  a  furnace  will  admit,  and  dropping  them  into  cold  water; 
this  causes  the  quartz  to  crumble  into  pieces  the  size  of  a  pea,  which 
are  further  reduced  in  a  Wedgwood  mortar  by  the  succesive  blows  of 
a  heavy  pestle  until  fine  enough  to  pass  through  a  No.  10  bolting-cloth 
sieve,  after  which  it  may  be  brought  to  the  state  of  an  impalpable  powder 
by  grinding  with  water  either  in  an  ordinary  hard  porcelain  mortar, 
or,  when  it  is  prepared  in  very  large  quantities,  by  one  of  the  powerful 
grinding  mills,  turned  by  steam,  in  use  at  the  large  manufactories. 

Clay. — This  is  a  hydrated  silicate  of  aluminum,  and  when  pure  may 
be  represented  by  the  formula  (2Al203,3Si02)  +  SHgO.  It  is  formed  by 
the  long-continued  action  of  air  and  water  upon  granite  rock,  the  dis- 
integration of  which  is  probably  due  to  both  mechanical  and  chemical 
causes.  Mechanically,  the  rock  is  continually  broken  down  by  variations 
of  temperature  and  by  the  congelation  of  water  witliin  its  minute  pores. 
Chemically,  the  action  of  water  containing  carbonic  acid  tends  to 
remove  the  potash  from  the  feldspar  and  mica  in  the  form  of  carbonate 
of  potash,  whilst  the  silicate  of  aluminum  and  the  quartz  are  separated 
by  the  action  of  the  water:  the  former,  being  the  higher,  is  separated 
from  the  heavy  quartz,  and,  wlien  again  deposited,  constitutes  clay. 

Kaolin  is  a  pure  quality  of  clay  from  which  such  impurities  as  sand  and 
mica  have  been  carefully  excluded  by  washing,  which  is  accomplished 
by  mixing  the  clay  with  a  large  amount  of  water  in  a  basin-shaped  vessel. 
It  is  at  first  thoroughly  stirred,  and  then,  after  sufficient  time  has  been 
allowed  for  the  sand  to  settle,  the  upper  or  lighter  layer  is  poured  or 
run  off  into  another  vessel.  It  is  then  permitted  to  stand  until  the 
kaolin  subsides  to  the  bottom  of  the  vessel:  the  water  is  siphoned  off; 


164 


PORCELAIN  TEETH. 


the  kaolin  is  tlicMi  dried,  when  the  mass  may  be  turned  out  and  the  l)ottom 
scraped  free  from  any  sand  found  adhering  to  it. 

Chiy  is  infusible  in  an  ordinary  furnace  when  heated  alone,  but 
readily  unites  with  feldspar,  at  high  temperature,  when  incorporated 
with  it,  and  is  an  element  of  strength  in  porcelain  compounds. 

Kaolin  should  be  thoroughly  mixed  with  the  other  ingredients  of  the 
body  while  in  the  dry  state,  and  complete  admixtures  may  be  attained  by 
passing  the  dry  body  through  a  No.  9  bolting-cloth  sieve. 

German  clay  is  imported  from  Europe,  and  is  used  to  manufacture 
various  articles  which  require  an  infusible  silicate  of  aluminum. 

Formulas  for  Body. 

The  formulas  for  bodies  and  enamels  used  by  manufacturers  to-day 
are,  of  course,  trade  secrets.  The  following,  taken  from  the  American 
System  of  Dentistry,  Vol.  II,  p.  962,  are  the  well-tested  standard 
bodies  of  Dr.  W.  R.  Hall,  and  give  an  idea  of  the  proportion  of  the 
ingredients : 

Bodies  for  Molded  Block  Teeth. 


Kaolin     . 

1  oz. 

German  clay  . 

; 

Silica 

3  " 

Silica     .... 

3 

Feldspar. 

.     18  " 

Feldspar 

.     18 

Titanium  oxide 

.     65  gr. 

Titanium  oxide 

,     65 

Starch,  10  gr.  to 

each  oz. 

Starch,  10  gr.  to  each  oz. 

II. 


i  oz. 


gr. 


It  was  formerly  the  custom  of  makers  of  molded  teeth  to  at  first  par- 
tially burn  or  biscuit-bake  the  teeth  or  blocks.  The  addition  of  starch 
or  gum  tragacanth  to  the  body  does  away  with  the  necessity  of  the 
"first  burning:,"  as  it  gives  the  teeth  sufficient  firmness  to  allow  of  their 
being  safely  handled  during  the  process  of  trimming,  which  must  be 
done  before  the  final  burning.  The  titanium  oxide  and  the  starch  are 
placed  in  a  mortar  and  ground,  at  first  without  water;  kaolin  and  silica 
are  then  added,  ground  together,  and  sifted  through  a  No.  9  bolting- 
cloth  sieve:  the  feldspar  is  then  added,  and  after  sieving  a  second  time 
the  mixture  is  ready  for  use,  and  should  be  kept  in  a  covered  glass  jar. 
As  it  is  often  desirable  to  have  in  stock  a  small  variety  of  bodies  of  dif- 
ferent shades,  it  will  be  found  of  great  convenience  to  have  attached  to 
each  jar  a  test  sample  of  the  body  which  has  been  burned  in  the  furnace, 
so  that  the  color  and  texture  may  be  ascertained  without  loss  of  time. 

In  preparing  bodies  and  enamels  for  use  in  molds  they  are  mixed 
with  water,  and  then  dried  to  the  consistence  of  dough,  when  they  are 
placed  in  the  molds  with  small  spatulas.  The  enamels  being  laid  in  the 
face  side  and  the  body  in  the  pin  sitle  of  the  molds,  these  two  halves  of 
the  mold  are  then  atljusted  to  each  other,  placed  in  a  strong  press  until 
in  complete  contact,  secured  by  a  strong  clamp,  and  exposed  to  a  heat 
sufficient  to  bake  the  starch  or  gum,  which  so  hardens  the  teeth  or 
blocks  that  they  will  withstand  a  very  consiilerable  amount  of  force 
without  danger  of  breaking.  During  the  biu-ning  of  the  teeth  the  starch 
or  gum  burns  out  without  injury  to  either  the  body  or  enamels. 


COLORS   USED  IN  MANUFACTURE  OF  PORCELAIN  TEETH.    165 

At  tlio  prosont  time  in  most  maiiii factories,  no  difference  is  made  in 
the  composition  of  the  enamels  and  l)odies  save  in  the  matter  of  their 
coh)rinif  constitnents.  'I'lie  body  is  generally  somewhat  yellower,  due 
to  the  titanium  oxide.  The  body  and  enamel  are  so  placed  and  prtj- 
portioned  on  the  face  side  of  the  mold  as  to  give  the  same  gradations 
of  color  to  the  artificial  tooth  which  are  observed  in  the  natural  teeth. 
We  have  dnis  "  point  "  and  "  base"  enamels  to  give  the  correct  colors  to 
these  portions  of  the  porcelain  tooth. 

In  bodies  used  for  carved  blocks  no  starch  need  be  used.  The  work 
being  done  entirely  by  hand  with  small  knives,  it  is  essential  that  the 
material  should  be  plastic  enough  to  cut  with  facility,  while  it  possesses 
sufficient  toughness  to  permit  of  careful  handling.  These  conditions 
are  obtained  by  simply  mixing  the  body  with  water,  the  kaolin  present 
furnishing  the  desired  plasticity. 


COLORS    USED    IN    THE   IVIANUFACTURE    OF   PORCELAIN   TEETH. 

The  colors  used  in  imitating  the  tints  of  the  natural  enamel,  dentin, 
and  gums  are  produced  by  thoroughly  incorporating  titanium  oxide  and 
preparations  of  gold,  tin,  platinum,  iron,  and  cobalt  with  the  mineral 
substances  of  which  porcelain  bodies  and  enamels  are  composed. 

Color  frits  are  made  by  grinding  the  metal  or  its  oxide  with  feldspar 
and  a  fine  cjuality  of  glass,  which  serves  as  a  flux  to  lower  the  fusibility 
of  the  enamel.  The  levigation  is  continued  until  a  very  fine  state  of 
di^^sion  is  reached,  after  which  they  are  biscuit-baked  in  the  muffle  of 
a  furnace.  ^Mien  cool  the  frit  is  removed  and  pulverized  in  a  Wedg- 
wood mortar,  which  has  first  been  thoroughly  scoured  out  by  grinding 
with  coarse  silica  to  effectually  remove  traces  of  any  coloring  pigment 
previously  prepared  in  the  same  mortar. 

In  grinding  prepared  platinum  or  gold-foil  the  feldspar  and  flux  are 
added  by  small  portions  at  a  time  until  the  greatest  degree  of  fineness 
is  attained.  The  shade  of  the  enamel  will  depend  largely  upon  the  state 
of  minute  division  of  the  metal  or  oxide.  As  an  example  it  may  be  stated 
that  distinctly  different  shades  may  be  made  from  portions  of  the  same 
mixture  by  reducing  one  lot  to  extreme  fineness  and  leaving  the  other 

comparatively  coarse. 

Frits. 
William  R.  Hall's  formulas  : 

Platinum  Frit.  Blue.  Platinum  Frit,  Gray. 


Platimmi  (dissolved  in  aqua  regia)    1  dwt. 
Feldspar.  .  .  .1  oz. 

Plate  glass       .  .  .   20  gr. 

Cobalt  Frit,  Azure  Blue. 

Smalt  (cobalt) 

Titanium  oxide 

Gold  frit  . 

Feldspar  ... 


Platinum  frit  . 
Titanium  oxide 
Gold  frit 


60 

gr. 

6 

t( 

60 

li 

1 

oz. 

Iron  Frit,  Gray. 


Iron  scale 
Titanium  oxide 
Gold  frit  . 
Feldspar 


30  gr. 

10  " 

100  " 


4gr 

1  " 

60  " 

1  oz. 


Pure  gold-foil 
Plate  glass  . 
Feldspar 


Gold  Frit,  Reddish-brown. 


12  gr. 

20  " 

1  oz 


166  roncELAiN  ti:i:tii. 

Dr.  William  U.  Hall's  directions  for  ])r('])aniio;  the  ])lalinum  and  gold 
frits  are  as  follows:  "  The  metal  for  the  pldfiinnn  frit  is  dissolved  in  boil- 
ing nitro-muriatic  acid,  care  being  taken  not  to  nse  more  acid  than  is  just 
sufficient  to  make  a  saturated  solution.  ^Yhen  cold  the  spar  and  glass 
are  added  and  mixed  with  a  glass  rod,  and  ])hice(l  in  a  clay  crucible  pre- 
viously washed  inside  with  ])owdere(l  (juartz  mixed  with  water.  A  cover 
must  be  closely  fitted  to  the  inner  edges  of  the  crucible,  the  joint  being 
carefully  closed  or  luted  with  clay  and  (piartz,  and  burned  as  has  been 
described." 

"The  metal  of  the  (/old  frit  is  diss(  lv<>d  in  cold  nitro-hydrochloric 
acid;  with  this  exception  it  is  treated  in  the  same  way  as  in  the  directions 
for  the  platinum  frit." 

Prof.  Wildman,  w^ho  called  the  gold  frit  "  silicdtc  of  gold,"  directed 
that  "coarse  felds])ar  120  gr.,  gold-foil  10  gr.,  flux  S  gr.  be  placed  in  a 
mortar  and  ground  until  the  gold  is  entirely  cut  up;  it  is  then  made  into 
a  ball,  placed  on  a  slide,  and  fused  in  the  muffle;  then  made  fine,  ready  for 
use."  His  gold  "  mixture  "  was  made  by  dissolving  8  grains  of  gold-foil 
in  aqua  regia,  to  which  were  added  and  well  stirred  300  grains  of  very 
finely  pulverized  feldspar.  \Mien  nearly  dry  the  mixture  was  formed 
into  a  ball  and  fused  on  a  slide  in  the  muffle  of  the  furnace,  after  which 
it  was  pulverized  and  kept  dry  for  use. 

Sponge  platinum  is  a  gray,  loosely  coherent  form  of  finely  divided  plat- 
inum that  readily  absorbs  certain  gases,  as  oxygen,  and  is  used  as  an  oxi- 
dizing agent. 

Sfonge  'platinum  is  made  by  dissolving  pure  platinum  filings  or 
scraps  in  six  times  their  weight  of  nitro-hydrochloric  acid  composed  of 
1  part  of  nitric  to  3  parts  oi  hydrochloric.  The  platinum  and  mixed 
acid  should  be  placed  in  a  clean  Florence  flask  and  heat  gently  applied 
by  means  of  a  sand  bath,  for  the  purpose  of  facilitating  the  action  of  the 
acid  on  the  metal.  The  heat  should  not  be  too  great,  otherwise  the  effer- 
vescence will  be  so  violent  that  a  portion  of  the  mixture  may  be  ejected 
from  the  flask.  Shoidd  effervescence  cease  entirely  before  all  the  metal 
is  dissolved,  the  fluid  must  be  decanted  and  more  acid  added  until 
the  last  particle  of  the  platinum  disappears.  The  solution  is  then  poured 
into  an  evaporating  dish  and  evaporated  on  the  sand  bath  until  the  mass 
is  nearly  dry  an<l  the  resulting  salt  assumes  the  crystalline  form.  At  this 
part  of  the  operation  care  must  be  taken  that  the  temperature  of  the 
sand  bath  is  kept  below^  450°  F. ;  above  that  point  decomposition  of  the 
platinic  chloride  takes  place,  w^hen  a  portion  of  the  chlorine  is  driven  off, 
causing  a  precipitate  of  platinous  chloride,  which  is  of  a  greenish-gray 
color  and  insoluble  in  water.  If,  however,  no  such  accident  occurs,  the 
platinic  chloride  will  be  of  a  reddish-brown  color,  very  delicjuescent  and 
freely  soluble  in  water.  The  crystallized  salt  is  dissolved  in  pure  dis- 
tilled water,  and  allowed  to  stand  until  it  becomes  perfectly  clear,  when 
it  is  to  be  filtered,  after  which  a  cold  saturated  solution  of  ammonium 
chloride  (sal  ammoniac)  is  gradually  added  to  the  platinic  chloride  until 
all  precipitation  ceases.  When  the  precij)itate  has  entirely  settled  it  is 
coflected  by  pouring  off  the  liquid,  thoroughly  washing  the  spongy  metal, 
drying,  and  placing  away  for  future  use  in  small  glass  jars. 

Iron  scale  is  a  loose  coating  of  oxid  which  forms  on  heated  iron  during 


ENAMELS  FOR   PORCELAIN   TEETH. 


1G7 


the  j)roco.ss  of  forging;  when  conihiiied  with  spar  it  makes  an  exceedingly 
natnral  bine-gray  color,  suitable,  when  toned  by  combination  with  other 
frits,  as  tlesignated  in  the  formula  of  Dr.  Hall,  for  the  cutting  edges  of  the 
teeth  of  yoiuig  persons. 

Cobalt,  which  has  been  mentioned  as  one  of  the  occasional  coloring 
ingredients  in  enamels,  is  what  is  known  in  commerce  as  "smalt."  It  is 
sometimes  used  in  producing  the  brighter  shades  of  blue.  It  is  not,  how- 
ever, a  permanent  color,  and  it  requires  to  be  associated  with  some  other 
color,  such  as  platinum,  to  prevent  it  from  being  lost  during  the  burning 
of  the  teeth. 

In  preparing  coloring  frits  it  should  be  borne  in  mind  that  a  too 
high  or  long-continued  heat  may  reduce  the  oxides  to  a  metallic  state, 
and  thus  ruin  them  for  use  as  coloring  pigments.  The  burning  should 
either  be  done  in  the  muffle  of  the  furnace  or  in  a  white-clay  crucible 
provided  with  a  top  securely  luted  in  and  made  perfectly  tight  with  a  mix- 
ture of  silica  and  kaolin,  for  the  purpose  of  protecting  the  frit  from 
the  action  of  the  fuel  gases.  The  burning  should  be  done  at  a  tempera- 
ture sufficiently  high  to  glaze  the  frit,  and  the  crucible  need  not  be  placed 
in  the  furnace  until  that  point  has  been  nearly  attained,  otherwise  the  first 
might  deteriorate  in  its  color-giving  qualities  by  too  long  exposure  to 
heat. 

ENAMELS  FOR  PORCELAIN  TEETH. 

The  enamels  of  Professor  Wildman  were  more  fusible  than  those  of 
William  R.  Hall,  and  w^ere  probably  not  as  w^ell  adapted  for  molding 
and  general  manufacturing  purposes  as  were  those  of  the  latter,  though 
in  translucency,  texture,  and  color  they  were  unsurpassed. 

The  making  of  bodies  and  enamels  and  their  application  require  both 
skill  and  experience.  There  should  also  be  a  correct  relation  of  fusing 
points  between  bodies  and  enamels.  As  the  fusibility  of  the  bodies  of 
Hall  and  Wildman  probably  differ,  it  would  not  do  to  use  the  enamels 
of  one  with  the  bodies  of  the  other. 


Professor  Wildman's  Formulas  for  Point  and  Base  Enamels. 


No.  1,  for  Points  (Gray). 

Feldspar           .          .          .  .  1  oz. 

Silicate  of  gold           .          .  .  6  gr. 

Prep,  sponge  plaiinum        .  .  4   " 

Flux                   .          .          .  .  20  " 

No.  3,  Yellow. 

Feldspar           .          .          .  .  1  oz. 

Titanium  oxide           .          .  .  8  gr. 

Prep,  sponge  platinum        .  .  4  " 

Gold  mixture    .           .          .  .  25   " 

Flux        .          .          .          .  .  24  " 


Feldspar 

Sponge  platinum  . 
Light  cobalt  ashes 
Flux  . 


No.  2,  Neck  or  Base  (Yellow). 

Feldspar            .           .          .          .  1  oz. 

Titanium  oxide           .          .          .  8  gr 

Prep,  sponge  platinvun        .          .  4 

Flux 24  " 


No.  4,  Gray. 

Feldspar 

Titanium  oxide 

Prep,  sponge  platinum 

Light  cobalt  ashes  . 

Flux      .... 


No.  5,  Blue 


1  oz. 
3  gr. 
2-3  ^" 
24  " 


1    oz 

Ugr 

4     " 

4     " 

24     " 


168 


PORCELAIN  TEETH. 


Dk.  William  R.  Hall's  Fohmilas  for  Enamei-s. 

It  will  l)c  observed  that  the  enamels  of  Dr.  Hall  have  no  flux  as  an 
ingreilient  otlier  than  tliat  which  is  contained  in  the  different  frits.  In 
this  respect  thev  differ  materially  from  tiie  formulas  of  Prof.  Wildman. 
On  the  ground  that  fluxes  give  a  glassy  surface  to  the  finished  teeth 
and  decrease  the  beauty  of  good  spar,  Dr.  Hall  asserts  that  none  should 
be  used  in  enamels. 


Platinum-gray,  No.  1. 
Plat. -gray  frit 


Feldspar 
Starch 

No   2. 

Plat  -gray  frit 

Feldspar 

Starch 


1  gr 
1  oz. 

15  gr. 


2gr. 

1  oz. 

15  gr. 


Platinum-gray,  Xo.  4. 

Plat.-graj'  frit        .       4  gr. 
Feldspar       .  1  oz. 

Starch  .  .      15  gr. 

Gold -yellow.  No.  1. 

Titanium,  pure  .  1  gr. 

Gold  frit       .  .  2   " 

Starch  .  15    " 

Feldspar       .  .  1  oz. 


Platinum-blue,  No.  1 

Plat. -blue  frit 

Feldspar 

Starch 

No.  3. 

Plat.-blue  frit 

Feldspar 

Starch 

Platinum-blue,  No.  5. 

Plat.-blue  frit         .        5  gr. 
Feldspar       .  .       1  oz. 

Starch  .  .      15  gr. 


>.  1 

1 

gr- 

1 

oz. 

15 

gr. 

3 

gr. 

1 

oz. 

15 

gr. 

Gold-yellow,  No.  2. 


Titanium,  pure 
Gold  frit       . 
Starch 
Feldspar 


^Igr. 

4    " 

15   " 

1  oz. 


Iron-gray,  No. 

4. 

Iron-gray  frit 

4gr. 

Feldspar 

loz. 

Starch 

15  gr. 

No.  6. 

Iron-gray  frit 

6gr 

Feldspar 

1  oz 

Starch 

15  gr 

Iron-gray,  No.  8. 
Iron-gray  frit         .       S  gr. 


Feldspar 
Starch 


1  oz. 
15  gr. 


Gold-yellow,  No.  3. 


Titaniiun,  pure 
Gold  frit       . 
Starch 
Feldspar 


Broivn-yellow,  No.  1. 


Titanium,  pure 
Platinum  frit    . 
Gum  frit 
Feldspar 
Starch 


1  gr. 
1  " 
4  " 
1  oz. 
15  gr. 


Brown-yellow,  No.  2. 

Titanium,  pure 

Platinum  frit    . 

Gum  frit 

Feldspar 

Starch     .... 


3gr. 

6  " 

15   " 

1  oz. 


2gr. 
2  " 
8  " 
1  oz. 
15  gr. 


GUM   FRIT    (PURPLE    OF   CASSIUS). 

Gum  frit,  as  its  name  implies,  is  for  the  purpose  of  imparting  the  pink 
color  to  the  gum  portion  of  a  gum  section.  It  derived  its  name  of  "  Pur- 
ple of  Cassius  "  from  the  Gernmn  chemist,  Andreas  Cassius. 

The  dry  method,  originated  by  the  late  Prof.  ^Yildman,  is  the  one 
now  employed  by  manufacturers  of  porcelain  teeth  in  the  preparation  of 
this  frit.  Pure' silver  240  gr.,  pure  gold  24  gr.,  and  pure  tin  17^  gr. 
are  placed  in  a  crucible,  with  sufficient  borax  to  cover  the  mass,  and 
meltetl.  In  order  to  ensure  a  thorough  mixture  of  the  diff'erent  metals 
the  melted  mass  .should  be  poured  from  a  height  into  a  vessel  of  cold 
water,  and  this  process  of  granulation  should  be  repeated  at  least  three 
times;  but  at  every  melting  the  alloy  should  l)e  well  covered  with  borax 


GUM  FRIT.  169 

to  prevent  loss  of  tin  by  oxidation.  The  vessel  into  which  the  molten 
mass  is  ponred  shonld  he  a  woodcMi  one. 

The  component  parts  of  the  alloy  have  now  been  thoronghly  incor- 
porated, the  next  step  is  to  collect  the  granulated  mass  and  separate  from 
it  any  adherent  particles  of  glass  or  borax.  The  metal  is  then  put 
into  a  glass  or  porcelain  evaporating  dish  (the  Berlin  porcelain  is 
the  best),  and  sufficient  chemically  pure  nitric  acid  is  added  to  cover 
the  rnetal.  The  dish  is  now  placed  over  a  sand  bath,  and  gentle  heat 
applied  and  continued  until  chemical  action  ceases.  If  at  this  point  it 
is  found  that  all  the  metallic  particles  ai-e  dissolved,  the  dish  may  be 
removed  from  the  bath.  Should  any  solid  particles  be  found  in  the 
solution,  a  little  more  nitric  acid  must  be  added  and  the  operation  con- 
tinued until  all  are  dissolved.  The  silver  having  been  entirely  dissolved 
by  the  nitric  acid,  the  solution  should  be  poured  off  and  the  remaining 
oxide  carefully  washed  until  the  last  trace  of  silver  is  removed.  After 
several  washings  with  a  large  quantity  of  pure  warm  water  the  latter 
should  finally  be  tested  with  a  clear  solution  of  common  salt,  and  if  it 
remains  clear,  without  show  of  milkiness,  the  silver  is  all  removed. 
When  the  oxide  is  sufficiently  washed  the  purple  of  Cassius  should  be 
dried  by  gently  heating,  after  which  it  is  ready  to  be  incorporated  with 
the  silicious  materials. 

The  process  of  making  gum  enamel  is  divided  into  three  stages: 
first,  the  preparation  of  the  oxide;  second,  fritting,  or  by  the  aid  of 
heat  uniting  the  metallic  oxide  with  the  silicious  base;  third,  diluting 
the  frit  so  as  to  form  the  desired  shade.  The  frit  is  formed  by  mixing 
8  grains  of  the  metallic  oxide  (purple  of  Cassius)  with  700  grains  of  feld- 
spar and  175  grains  of  a  flux.  The  oxide  is  placed  in  a  smooth  Wedg- 
wood mortar  and  ground  as  fine  as  it  is  possible  to  get  it.  The  flux  is 
then  added  in  small  quantities  and  the  levigation  continued,  after  which 
the  feldspar  may  be  added  and  treated  similarly.  It  is  of  the  highest 
importance  that  the  mass  be  reduced  to  the  utmost  degree  of  fineness, 
and  an  expert  workman  will  spend  six  or  eight  hours  at  least  in 
levigating  the  quantity  given  in  the  formula.  While  the  mass  is  being 
ground  in  the  mortar  foreign  substances,  such  as  small  particles  of  wood, 
etc.,  must  be  carefully  excluded;  otherwise  during  the  vitrefying  process 
these  will  be  converted  into  carbon,  which  will  be  sure  to  reduce  a  por- 
tion of  the  gold  in  fine  metallic  globules  distributed  throughout  the 
mass. 

The  vitrefying  or  fritting  process  consists  in  packing  the  mass,  after  the 
most  thorough  levigation,  in  the  whitest  sand  crucible  that  can  be  ob- 
tained. (Dark-colored  crucibles  are  liable  to  injure  the  frit  by  contami- 
nation with  iron.)  This  must  be  provided  with  an  accurately  fitting 
cover  made  of  the  same  material,  or  a  suitable  top  may  be  formed  of  a 
piece  of  slide  such  as  is  used  in  burning  continuous-gum  work.  Before 
placing  the  frit  in  the  crucible  the  interior  surface  of  the  latter  should 
receive  a  thin  coating  of  very  fine  cpiartz,  made  into  a  paste  with  water, 
to  prevent  the  frit  from  adhering  to  it  during  fusion.  The  frit  in  the 
dry  state  is  then  packed  in,  and  the  cover  tightly  luted  to  its  place  wdth 


170 


PORCELAIS   TKKTH. 


kaolin.  The  rrucil)l(>  is  then  buried  in  a  stronfr  anthracite  coal  fire, 
remaining  there  until  the  contents  are  fused.  The  time  recjuired  to 
do  this  will  depend  u])on  the  size  of  the  crucible  and  the  intensity  of 
the  heat.  Anv  ordinary  coal  stove  provided  with  a  good  draught  will 
answer,  but  the  fuel  must  i)e  packed  around  and  over  the  crucible,  and 
the  heat  carried  to  the  highest  attainable  ]>oint.  Usually  about  two 
hours  will  be  retjuired  to  thoroughly  fuse  the  mass,  after  which  it  is 
removed  from  the  fire  and  j)ermitted  to  cool. 

The  vitrefied  mass  is  removed  from  the  crucible  by  breaking  the  latter. 
Every  particle  of  adhering  ({uartz  or  portions  of  the  crucible  should 
be  cleared  from  the  surface.  It  is  then  pulverized  to  a  fineness  which 
will  allow  it  to  pass  through  a  No.  10  bolting-cloth  sieve,  and  is  ready 
for  the  third  stage  in  the  preparation  of  gum  enamel,  which  consists 
of  diluting  the  frit  with  the  proper  amount  of  feldspar.  As  the  strength 
of  the  coloring  pigment  varies  according  to  the  degree  of  fineness 
attained  during  the  levigation,  it  is  usually  necessary  to  make  several 
tests  in  order  to  arrive  at  the  desired  shade.  This  is  accomplished  by 
mixing  separately  several  different  lots  in  the  following  proportions: 


Gum  frit   . 

.      1  part ; 

Gum  frit   . 

.      1  part; 

Gum  frit   . 

1  part ; 

Feldspar   . 

.      2  parts. 

Feldspar    . 

.      3  parts. 

Feldspar    . 

.     4  parts 

These  are  applied  to  marked  pieces  of  porcelain  body  and  fused  in 
the  usual  wav,  the  result  determining  the  proportions  necessary  to  pro- 
duce the  desired  shade. 


Formula   for   Flux   (Glass)  for   Reducing  tfie  Fusixg   Point 

OF  Enamels. 

White  bottle-glass,  which  does  not  contain  lead  or  iron,  may  be  used 
as  "flux"  to  reduce  the  fusing  point  of  enamels,  but  owing  to  the  un- 
certainty of  the  composition  of  glass,  most  of  the  manufacturers  of 
porcelain  teeth  make  a  fine  glass  for  this  purpose  after  the  following 
formula,  the  ingredients  of  which  are  first  ground  separately,  then 
thoroughly  mixed,  and  placed  in  a  white  crucible  provided  with  a  cover 
(which  must  be  tightly  luted)  and  thoroughly  fused.  If  perfectly  pure 
materials  are  used,  the  result  will  be  an  exceedingly  brilliant,  colorless, 
and   transparent  glass: 


Finely  pciwdered  silica 

"  "  .tr;lass  of  borax 

Potassium  car])oiiate     . 


12  oz. 
3  " 
3    '• 


FORMULAS  FOR   CONTINUOUS-OUM    WORK. 


171 


FoKMl'LAS    FOR    CoNTINUOTTS-CrM    WoRK. 

Bodies  and  tMiaincls  intended  for  u.se  in  the  "  eontinuous-guni  "  pnx-- 
ess  nuist  necessarily  be  more  fusible  than  the  materials  of  which  teeth 
are  composed,  in  order  diat  the  latter  may  not  be  affected  by  the  three 
heatings  the  denture  must  be  exposed  to  i)efore  it  is  completed.  It  will 
therefore  be  noticed  that  an  unusual  amount  of  flux  enters  into  their 
composition.  The  formulas  herein  given  are  those  of  well-known 
experts  in  continuous-gum  work. 

Continuous-Gum  Formulas  of  Dr   Hunter. 


Flux:  Quartz 

8    oz 

Calcined  borax 

4     " 

Caustic  potash 

1     " 

Granulated  Body:  Spar    . 

2    oz 

Quartz 

^  " 

Kaolin 

1  ii 

Body:  Flux,  as  above 

1    oz 

Asbestos 

2     " 

Granulated  body  . 

n " 

Gum  Enamel:     Flux,  as  above 

1    oz 

Fused  spar 

1    " 

English  rose-re 

d    40    gr 

Form 

ULAS    OF 

Grannlated  Body:  Quartz 

20    gr 

Spar  . 

24     " 

Caustic  pot£ 

ish  1     " 

Titanium    2 

gr.-l  oz. 

Flux:  Quartz,  very  fine 

18    dwt. 

Spar 

10       " 

Glass  of  borax  . 

2       " 

Cryolite     . 

1       " 

Caustic  potash  . 

10    gr. 

Titanium            .           1; 

gr.-l  oz 

Gum  Enamel:  Gum  frit  of  (S. 

S.White)    . 

4J  dwt 

Flux    without 

titanium      . 

16       " 

Gfanulated 

body  . 

11       " 

Cryolite 

7       " 

Fuse  in  crucible  to  form  glass;  when  cold 
reduce  to  powder. 

Fuse  in  crucible,  and  powder  to  pass 
through  No,  50  wire  sieve. 

Grind  the  first  two  articles  very  fine,  then 
add  granulated  body,  which  is  mixed 
with  the  fine  without  grinding. 

Grind  very  fine  and  -semi-fuse  in  crucible; 
powder  coarsely  for  use. 


Grind  fine  and  fuse  on  slide  in  furnace; 
powder  coarsely  for  use. 


Fuse  same  as  above,  and  grind  very  fine. 


Fuse  and  grind  for  use. 


Dr.  Moffit's  Formula  for  Continuous-Guai  Body. 
Body:  Spar  .  .  .      12    oz. 

Quartz       .  .  -42   " 

Bohemian  glass  .      60    gr.       [  Grind  coarsely. 

French  china      .  .      35     " 

German  clay       .  .       2    dwt 


No  gum-enamel  formula  came  with  this.     Dr,  Smith's  formula  for 
gum  enamel  will  do  for  the  above,  minus  the  cryolite. 


172 


PORCKLA  IN  TKKTII. 


THE    PROCESS    OF   MANUFACTURE    OF   PORCELAIN   TEETH. 

Brass  Molds  for  Porcelain  Teeth. — The  mamifacture  of  molded 
teetli  as  carried  out  ii])on  tlie  extended  scale  of  the  present  day,  to  meet 
the  (hMnands  of  tlie  trade,  recjuires  the  use  of  a  large  number  of  hrass 
molds  of  various  sizes  and  forms.  In  the  l)est  factories  a  "  pattern  " 
mold  of  each  of  these  is  kept  as  a  standard  to  preserve  the  uniformity 
of  the  product.  It  is  not  used  in  molding  teeth,  but  serves  as  a  pattern, 
from  which  are  secured  the  "  duplicate  "  molds  actually  employed  in 
manufacture. 

Mold-making  includes  the  carving^  of  the  plaster  blocks,  making  the 
plaster  pattern  of  the  mold,  casting  it  in  hard  brass  or  bronze,  and 

the  "  cutting  "  or  finishing  of  the 
mold. 

The  plaster  blocks  constitute 
the  design,  and  are  a  complete  set 
of  block  teeth  carv^ed  in  plaster 
with  allowance  made  for  shrinkage 
and  other  changes  which  take  place 
in  the  vitref}ing  process.  This 
part  of  the  work  must  be  done  by 
an  artist,  and  one  who  has  know- 
ledge of  the  several  classes  of  hu- 
man teeth.  These  designs  should 
always  be  made  from  natural 
teeth. 

Dr.  J.  Leon  ^Villiams,  of  Lon- 
don, is  at  the  present  time  pre- 
paring a  set  of  molds,  36  in  num- 
ber, providing  12  t\'pes,  with  3 
sizes  in  each  tx'pe.  These  molds, 
it  is  hoped,  will  provide  a  range  of 
selection  for  any  but  the  most  extraordinary  cases.  The  original  models 
are  being  carved  with  the  greatest  attention  to  anatomical  form  and  are, 
in  the  sets  for  edentulous  cases,  to  be  articulated  in  the  original  to  provide 
for  a  minimum  amount  of  grinding  in  articulation  of  the  porcelain  re- 
productions. The  plaster  blanks  are  arranged  on  a  rim  of  wax  similar  to 
articulating  wax;  the  gums  are  formed  of  paraffin  or  the  pink  combina- 
tion of  paraffin  and  wax;  broad  spaces  are  left  between  the  centrals; 
the  cuspid  and  first  bicuspids  and  the  second  bicuspids  and  first  molars, 
as  sectional  blocks  for  an  entire  upper  denture,  are  divided  into  six 
pieces.  Each  block  must  be  provided  with  a  slight  excess  of  material 
at  the  joint,  to  afford  sufficient  latitude  in  fitting  them  together.  A  wall 
of  plaster  about  one-fourth  of  an  inch  in  thickness  is  rim  on  the  outside 
of  the  model,  so  as  to  include  the  entire  set  of  l)lanks ;  when  hard  enough 
it  is  trimmed  so  as  not  to  exceed  in  height  the  cutting  edges  of  the  tooth 
blanks,  varnished,  and  oiled;  an  inside  wall  is  then  made  of  plaster  of 
the  same  height  as  the  outside  one.  The  inside  wall  is  removed  when 
hard  in  one  piece;  the  outside  one  fs  cut  into  six  pieces  with  a  thin  saw 


Tooth  blanks  arranged  on  cast. 


THE  PROCESS   OF  MANUFACTURE   OF  PORCELAIN  TEETH.    173 

blade,  the  cut  being  made  between  the  centrals,  the  canines  and  l)icus- 
pids,  and  the  bicuspids  and  molars  at  the  spaces  shown  in  Fig.  115. 
The  sections  tluis  made  are  then  separated  from  the  model. 

Both  the  outside  and  inside  walls  are  trimmed,  varnished,  and  laid 
aside  to  dry.  The  removal  of  the  blanks  from  the  model  is  next  in 
order,  and  both  walls  are  given  a  coating  of  shellac  varnish.  Fig.  11 G 
shows  the  walls  made  for  a  lower  set  of  plaster  blocks.  The  walls  are 
now  to  be  placed  on  the  model  and  secured  in  position  with  twine  or 
wire;  they  are  then  oiled,  and  plaster  mixed  to  the  consistence  of  cream 
is  first  painted  over  the  surface,  as  representing  the  teeth,  w^ith  a  camel's- 
hair  brush,  when  the  residue  is  run  in  betw^een  the  inside  and  outside 

Fig.  116 


View  of  the  walls  and  cast,  separated. 


walls  and  allowed  to  set  thoroughly  before  removal.  If  the  plaster  has 
been  carried  into  all  depressions  and  interstices  between  the  walls,  a 
continuous  set  of  plaster  blocks  will  be  the  result.  These  are  separated 
into  six  sections  by  means  of  a  thin  saw  blade,  as  shown  in  Fig.  117, 
the  six  front  teeth  in  two  sections  of  three  each,  the  first  and  second  bicus- 


174 


PORCELAIN  TEETH. 


pids  of  each  side  in  two  otiier  sections;  the  molars  are  (Hvided  in  the 
same  may.  These  phistcr  blocks  now  recjuire  trimming  on  the  inside, 
the  carving  of  the  masticating  surfaces  of  the  bicuspids  and  molars  in 
imitation  of  the  natural  organs,  and  the  cutting  of  a  recess  for  the  pins, 
as  seen  in  Fig.  117. 

The  ends  of  the  blocks,  or  those  parts  technically  called  the  joints, 
must  be  trimmed  so  that  they  will  taper  sufficiently  to  ensure  their  safe 


Fig.  117 


k,^,  liiii^lietl 


delivery  from  the  plaster  mold,  as  shown  by  the  pin  sides  of  the  plaster 
blocks  in  Fig.  117.  If  not  properly  bevelled  at  all  points,  so  that  no 
undue  retention  will  occur,  it  may  be  necessary  to  remove  the  pattern 
blocks  piecemeal.  The  plan  of  such  a  mold  would  then  be  found  to  be 
defective  and,  as  may  readily  be  surmised,  it  would  not  be  possible  to 


Fig.  118 

B- 



% 

1 

,  -; 

-3 

" ~ 

J 

fro 

O^ 

m] 

-' 

M 

"31 

= 

-^ 

w 

_J 

^^ 

^ 

Foundation  plate. 


obtain  a  brass  mold  from  a  pattern  in  which  so  serious  a  fault  existed. 
After  these  details  have  received  careful  attention  and  the  blocks  have 


THE  PROCESS  OF  MANUFACTURE  OF  PORCELAIN   TEETH.    175 


been  triinined  and  carved  to  the  satisfaction  of  the  workman,  they  should 
receive  at  least  two  coats  of  shellac  or  sandarac  varnish. 

The  Plaster  Mold. — ^I'he  preparation  of  the  plaster  mold  is  the  second 
part  of  the  process  of  mold-making,  the  first  part  being  the  modelling 
of  the  designs  in  the  form  of  plaster  blocks.  These  designs  are  really 
the  foundation  of  the  whole  system,  and  require  in  their  production 
artistic  talent  and  knowledge  of  the  forms  of  the  different  t;y'pes  of  human 
teeth.  With  the  exception  of  the  cutting  or  finishing  of  the  brass  mold, 
.  the  rest  of  the  process  is  purely  mechanical. 

By  referring  to  Figs.  122  and  123  it  will  be  seen  that  the  finished 
mold  consists  of  five  pieces — the  face  side,  the  pin  side,  two  end  or 
crown  pieces,  and  a  key  piece.  These  pieces  have  all  to  be  made  in 
plaster  to  serve  as  patterns  from  which  to  cast  fac-similes  in  brass.  The 
plaster  blocks  are  arranged  on  a  foundation  plate.     This  plate  can  be 

Fig.  119 


Brass  frame. 


made  of  brass  or  zinc,  as  shown  in  Fig.  118,  5j  inches  long,  3  inches 
wide,  and  \  of  an  inch  thick,  with  oblong  recesses  to  receive  the  blocks — 
those  for  the  front  blocks  1  inch  long  and  I  an  inch  wide;  those  for  the 
bicuspids,  f  of  an  inch  long  and  h  an  inch  wide;  and  those  for  the  molars 
I  of  an  inch  long  and  %  an  inch  wide.  The  black  lines  on  the  plate  are 
used  as  guides  to  measure  from  in  placing  the  blocks ;  the  round  holes 
at  the  ends  are  to  receive  the  pins  seen  on  the  frames  in  Fig.  119. 

The  plaster  blocks  are  placed  on  the  foundation  plate  faces  upward, 
with  the  cutting  edges  opposite  to  each  other,  as  seen  in  Fig.  120,  and 
are  then  secured  in  position  with  beeswax,  clay,  or  putty,  which  also 
marks  the  correct  line  of  division  between  the  two  halves  of  the  mold. 
This  is  a  very  important  detail  of  mold-making;  upon  its  correct  man- 
agement depend  the  successful  application  of  the  enamels  and  the  safe 
delivery  of  the  molded  porcelain  blocks.  This  line  of  division  should 
extend  along  the  middle  of  the  cutting  edges  of  the  incisors  and  canines 


176 


PORCELAIN  TEETH. 


and  the  fjjum  cd^Q,  but  should  include  but  little  of  that  portion  of  the 
block  called  the  joint.  By  referring  to  Fig.  121  the  reader  will  see  that 
the  face  side  of  the  mold  gives  merely  the  distinct  outline  of  the  entire 
face  of  the  block,  and  that  the  bulk  of  the  block  is  rej)resented  in  the 
pin  side;  yet  the  edges  of  the  face  side  of  the  blocks  should  be  sufficiently 
well  defined  to  assist  in  holding  the  enamels  in  position  when  the  mold 
is  pressed  together.  The  front  blocks  are  secured  to  the  plate  -j^  of  an 
inch  from  its  centre  line;  the  bicuspid  blocks,  -^  of  an  inch  from  the 
line;  the  molar  blocks,  yg-  from  the  line.  The  side  blocks  are  arranged 
farther  apart  at  the  end  near  the  molars  than  at  the  other,  to  allow  for 
a  tapering  key,  as  shown  by  C  in  Fig.  123.  If  all  spaces  between  the 
block  and  the  foundation  plate  have  been  stopped  with  clay  or  putty, 
the  plate  with  arranged  blocks  is  ready  for  the  frame. 

The  frame  is  in  two  sections  made  of  polished  brass,  one  section  made 
to  articulate  with  the  other  by  means  of  pins  and  corresponding  holes,  as 
seen  in  Fig.  119.  The  inside  tapers  so  that  the  plaster  mold  when  hard 
may  deliver  without  difficulty.    These  frames  measure  4f  inches  in  length 


FiG.    120 


Pin  side  of  plaster  mold,  with  plaster  blocks  and  wax  in  position. 

and  2f  inches  in  width,  each  section  being  f  of  an  inch  high  with  a 
thickness  of  \  of  an  inch.  The  part  with  pins  is  well  oiled  on  its  inside 
and  placed  on  the  plate.  The  plaster  blocks  having  been  oiled,  the  plaster 
is  mixed  by  dropping  it  into  water  and  allowing  it  to  settle  without  stir- 
ring, so  as  to  exclude  air;  the  excess  of  water  is  then  poured  off;  the 
blocks  carefully  coated  with  thin  plaster  by  means  of  a  small  camel's- 
hair  pencil;  the  rest  of  the  plaster  is  then  poured  in  and  levelled  off  even 
with  the  top  of  the  frame  with  a  spatula.  When  the  plaster  becomes  hard 
the  plate  is  removed  and  the  face  side  of  the  pattern  is  secured. 

The  blocks  are  then  carefully  taken  from  the  face  side  of  the  plaster 
mold,  and,  if  any  of  the  edges  are  broken,  they  must  be  repaired  with 
wax  or  plaster  and  made  smooth.  After  the  removal  of  the  blocks  the 
mold  must  be  varnished  with  shellac  or  sandarac  and  allowed  to  dry 
thoroughly,  when  the  blocks  are  replaced.  The  space  between  the 
bicuspid  and  molar  blocks  is  filled  by  a  piece  of  wax,  as  seen  in  Fig.  120, 
to  form  the  depression  intended  for  the  end  pieces  and  key  in  the  pin 
side  of  the  mold.  The  whole  fixture  is  then  thoroughly  saturated  in 
clean  water,  the  surfaces  coated  lightly  with  oil,  and  the  other  section 


THE  PROCESS  OF  MANUFACTURE   OF  PORCELAIN  TFFTlf.    177 

of  the  brass  fnunc  [)lace(l  in  position  and  filled  with  j)laster  mixed  and 
applied  in  the  manner  previously  deseril)e<l;  this  forms  the  pin  side  of 
the  mold.  'J'he  two  sections  are  easily  separated  when  the  plaster  has 
hardened  sufficiently  by  introducing  a  knife  blade  between  them  and 
carefully  pi'ying  apart.  The  plaster  blocks  will  usually  be  found  in  the 
pin  side  of  the  mold,  because  the  greater  portion  of  the  block  is  embraced 
in  that  part  of  it,  and  consequently  offers  more  surface  for  retention 
than  does  the  face  side.  The  brass  frames  are  next  to  be  removed  from 
each  part  of  the  plaster  mold  by  tapping  the  former  gently  with  a  small 
wooden  mallet.  The  blocks  are  then  to  be  removed  from  the  pin  side  of 
the  mold;  this  must  be  done  with  the  greatest  care  by  inserting  a  sharp 
excavator  or  knife  point  under  the  block  and  gently  prying  it  out.  If 
any  part  of  the  mold  is  broken  and  carried  away  with  either  of  the  blocks, 
the  piece  may  be  fastened  back  to  its  proper  place  with  thick  shellac 
varnish,  or,  if  lost,  the  defect  may  be  repaired  with  beeswax. 

The  crowns  or  masticating  surfaces  of  the  bicuspids  and  molars  are 
formed  by  end  pieces  held  in  place  by  a  wedge-shaped  piece  of  brass, 

Fig.  121 


Face  side  of  plaster  mold,  with  temporary  key. 

as  shown  by  A,  B,  and  C,  Fig,  123.  The  wax  seen  in  Fig.  120  must 
be  taken  away  from  between  the  side  blocks,  and  the  blocks  removed 
and  carefully  cleaned;  the  space  formed  by  this  piece  of  wax  must  be 
trimmed  so  as  to  increase  its  width  about  ^  of  an  inch,  its  floor 
made  perfectly  flat  and  its  sides  perpendicular,  and  arranged  to  taper 
toward  the  end  nearest  the  front  blocks,  where  it  should  be  slightly 
narrower  than  at'the  molar  end  of  the  space.  This  space  at  its  floor  and 
sides  must  be  level  and  true,  or  the  crown  pieces  and  key  A,  B,  C, 
(Fig.  124)  will  not  fit  well  in  the  finished  mold;  the  surface  of  the  recess 
Is  then  varnished.  A  temporary  key  of  brass  is  placed  midway  in  this 
space  and  secured  with  wax,  as  shown  in  Fig.  121,  and  allowed  to  extend 
a  quarter  of  an  inch  beyond  the  end  of  the  mold.  The  plaster  mold 
is  then  oiled  and  put  In  water  to  drive  out  the  air;  the  side  blocks  are 
oiled  and  put  in  place;  the  face  side  of  the  mold  is  oiled  and  put  in  posi- 
tion, and  the  two  sides  tied  together.  Plaster,  mixed  thin,  is  then  run 
into  the  spaces  on  each  side  of  the  temporary  key,  extending  beyond  the 
mold  to  the  end  of  the  key.  After  the  plaster  is  hard  the  temporary 
key  is  carefully  drawn  out  by  means  of  pliers,  when  the  crov/u  pieces 

12 


178 


PORL'ELAIX  TEETH. 


may  he  easily  reinoverl.  All  tiie  parts  of  the  plaster  mold  are  now  to  be 
thoroughly  dried  by  gentle  heat;  grooves  are  then  eut  around  eaeh  block 
in  both  sides  of  the  mold  to  allow  for  the  escape  of  the  excess  of  body 
and  enamel  usual  in  molding  teeth.  All  parts  of  the  plaster  mold  must 
be  made  as  smooth  and  ])erfect  as  possible,  as  its  condition,  whether 
Dood  or  bad,  is  duplicated  in  the  brass  castings,  where  it  is  much  more 


Face  side  nf  brass  mold. 


difficult  to  correct  imperfections  or  faults  than  in  the  plaster.  ^Yhen 
entirely  finished  and  thoroughly  dried  all  the  parts  of  the  plaster  mold 
are  to  be  varnished  with  shellac  and  allowed  to  dry  thoroughly,  when 
they  are  ready  to  be  sent  to  the  foundry  to  be  cast  in  hard  brass. 

Fig.  122  shows  the  face   side   of  the  finished  brass  mold.     Fig.  123 
shows  the  pin  side:  .4  and  B,  the  crown  pieces;  C,  the  key.     Retaining 


Fig.  123 


Pin  side  of  brass  mold. 


pins  of  brass  are  put  in  to  prevent  movement  of  the  crown  piece  during 
molding;  the  heads  of  these  are  seen  in  Fig.  123  between  the  molar  and 
bicuspid  blocks. 

Cutting  and  Finishing  Brass  Molds. — Brass  or  bronze,  like  other  hard 
metals,  when  cast  will  shrink  somewhat,  and  thus  the  brass  casting  be- 
comes smaller  than  the  plaster  model  of  which  it  is  a  fac-simile:  in  finish- 


THE  PROCESS  OF  MANUFACTrRE   OF  PORCELAIN  TEETH.    179 

ing  the  surface  of  the  depressed  teeth  and  gums  in  the  l)rass  mold  the 
workman  will  necessarily  enlarge  to  some  extent  the  reversed  represen- 
tation of  the  blocks  to  the  original  size  of  the  plaster  models,  and  the 
work  should  he  tlone  with  such  precision  that  the  latter  can  he  placed 
in  the  brass  mold  and  fit  as  though  they  had  been  molded  in  it. 

After  fitting  together  the  two  sides  of  the  mold,  trial  blocks  of  plaster 
sliould  be  made  to  ascertain  if  the  outlines  of  the  blocks  meet  properly. 
The  trial  blocks,  made  by  pressing  plaster  between  the  two  halves  of  the 
mold,  will  indicate  any  defect  in  adjustment.  If,  however,  it  is  found 
that  the  outline  edges  are  quite  together,  and  that  the  relation  of  one  half 
to  the  other  is  correct,  the  guide  pins  are  to  be  put  in,  in  order  that  the 
relation  of  the  parts  be  permanently  fixed.  This  is  done  by  firmly  hold- 
ing the  two  parts  of  the  mold  in  a  steel  clamp,  and  then  drilling  the  holes 
for  the  pins  entirely  through  each  side  with  a  ^  of  an  inch  drill.  One 
of  the  guide  pins  is  placed  in  the  face  side  of  the  mold  opposite  the 
right  central,  the  other  in  the  pin  side  opposite  the  left  molar.  They 
must  be  permanently  screwed,  one  on  each  side  of  the  mold,  as  shown 
in  Figs.  122  and  123.  After  the  holes  are  drilled,  the  one  in  the 
face  side  opposite  the  central  and  the  one  in  the  pin  side  opposite  the 


Fig.  124 


Crown  piece. 


Key. 


Crown  piece. 


left  molar  must  be  screw-tapped  to  receive  the  screw  end  of  the  guide 
pins ;  the  other  end  of  the  pins  must  taper  slightly  near  its  extremity  so 
as  to  freely  enter  the  hole  opposite  to  it,  but  the  pins  must  fit  close  enough 
to  prevent  lateral  movement  wdien  the  two  parts  of  the  mold  are  quite 
together.  These  pins  should  be  madr  of  steel  w^ire  not  less  than  -^ 
of  an  inch  in  thickness.  The  outside  of  the  mold  is  then  to  be  squared 
and  finished;  this  may  be  done  either  in  a  lathe  or  by  filing  guided 
by  the  try-square  and  the  callipers,  for  it  is  very  important  that  the 
mold,  wdien  the  two  parts  are  together,  should  be  uniform  in  thick- 
ness and  perfectly  level,  as  there  is  danger,  if  these  conditions  are  not 
secured,  of  its  being  sprung  out  of  shape  by  the  press  in  molding  teeth. 
The  next  step  toward  the  completion  of  the  mold  is  the  fitting  of 
the  end  pieces  in  the  space  between  the  back  blocks;  the  floor  of  the 
space  must  be  filed  perfectly  flat  and  level,  and  the  side  made  perpendic- 
ular; the  crown  pieces,  where  they  are  in  contact  with  the  key,  are  made 
smooth  and  true;  the  taper  key,' 0  (Fig.  124),  is  made  to  fit  between 
them  and  holds  the  crown  pieces  securely  against  the  perpendicular  walls 
of  the  space  alluded  to  above  during  the  operation  of  molding  teeth. 
This  key  is  made  longer  than  the  crown  pieces,  so  that  it  can  be  driven 
betw^een  them  with  a  wooden  mallet  to  facilitate  its  removal.    To  prevent 


180 


FORCE  LA  IS   TKETII. 


tiie  crown  pipfos  from  slidintf  hack  while  the  mold  is  iiiidcr  pressure, 
two  hrass-headed  ])ins  are  riveted  in  the  j)in  side  of  the  mold  hetween 
the  bicuspid  and  mohir  l)lock,  as  shown  in  Fig.  12o,  the  ])in  l)eing  partly 
in  the  mold  and  j)artly  in  the  crown  ])ieces. 

The  cutting  and  smoothing  of  the  gums  and  fa(  es  of  the  teeth  in  the 
castings  is  not,  as  is  generally  helieved,  a  very  difHcult  mechanic  al  o})era- 
tion;  it  does,  however,  require  artistic  skill  and  judgment.  The  fine  lines 
of  the  plaster  pattern  are  made  less  distinct  by  the  casting  of  the  metal. 
The  gravers  (Fig.  125)  are  to  be  employed  to  restore  the  definiteness  of 


Fig.  125 


Gravers  of  Stub's  steel. 


outline  and  contour,  and  great  care  must  be  taken  in  doing  this  to  avoid 
change  or  obliteration  of  the  characteristic  features  of  the  original  pat- 
tern. The  gravers  should  be  of  the  best  quality  of  steel  tempered  to  a 
straw  color;  they  must  be  kept  ground  to  a  long  bevel  and  a  keen  edge, 
the  latter  being  made  by  means  of  an  Arkansas  stone;  the  gouge-shaped 
graver  is  used  at  first  to  cut  a  clean  and  smooth  sin-face  on  the  part  of 
the  mold  representing  the  faces  of  the  front  teeth.  A  plaster  set  of 
teeth  should  then  be  made,  which,  on  comparison  with  the  original  pat- 
terns, will  indicate  that  further  cutting  is  needed  to  bring  the  mold  to 
correspond  exactly  with  them.  The  pin  side  of  the  mold  will  recjuire 
trimming  with  the  flat  or  chisel-shaped  graver  to  give  it  a  smooth  sur- 
face, and  to  bring  the  size  to  that  of  the  original  pattern,  which  should 
fit  perfectly  into  the  brass  mold  as  though  it  had  been  molded  there; 
and  this  is  a  good  test  for  the  accuracy  of  the  brass  casting. 

During  the  cutting  repeated  trials  should  be  made  with  ])laster  to  see 
if  the  edges  come  properly  together  with  no  overlapping;  and  as  the  cut- 
ting proceeds  it  will  be  necessary  for  the  workman  to  frequently  see  the 
reverse  aspect  of  the  teeth;  this  he  does  with  black  try-wax,  Avhich  is  made 
by  mixing  beeswax  and  lampblack  with  a  few  drops  of  turpentine.  Small 
pieces  of  this  wax  are  held  in  the  hand  while  cutting,  the  warmth  o^  the 
hand  being  sufficient  to  soften  it;  in  this  way  the  mold-maker  is  able 
to  take  impressions  of  the  concavities  of  the  teeth  as  the  work  proceeds. 
Care  is  recjuired  in  carving  the  original  patterns  to  form  the  margins 
around  the  necks  of  the  teeth,  so  that  they  are  sharp  and  suflficiently  well 
defined  to  keep  the  gum  enamel  from  mixing  with  the  crown  enamel 
when  the  mold  is  pressed.  The  mold-trimmer  must  be  cautioned 
against  obliterating  this  line  of  demarcation  between  crowns  and  gum. 


THE  PROCESS  OF  MANUFACTURE  OF  PORCELAIN   TEETH.    181 

When  the  mold  is  complete  in  respect  to  size  cind  form  of  the  teeth, 
another  set  of  plaster  blocks  should  be  made  in  it,  for  the  purpose  of 
determining  whether  the  blocks  leave  the  mold  readily  when  slightly 
tapped  with  a  wooden  mallet.  If  the  blocks  are  difficult  to  remove,  it 
will  be  evident  that  remaining  points  exist  which  retard  their  delivery; 
these  are  easily  discovered  by  the  abrasion  they  make  upon  the  plaster, 

Fig.  12B 


ice  side  of  mold  for  anterior  plain  rubber  teeth. 


and  such  points  should  be  bevelled  sufficiently  to  allow  the  blocks  to  drop 
from  the  mold  without  injury  when  gently  tapped  by  the  mallet  on  its 
sides  or  ends.  Finally,  small  holes  are  to  he  drilled  in  the  pin  side  of  the 
mold  for  the  platinum  pins;  these  holes  are  drilled  perpendicularly  to 
the  face  of  the  mold  and  parallel  with  each  other,  five  for  each  front 
block,  four  for  the  biscuspid  blocks,  and  three  for  the  molar  blocks.    The 


Fig.  127 


Pin  side  of  mold  for  anterior  plain  rubber  teeth. 

mold  is  now  to  be  thoroughly  cleansed  of  all  particles  of  brass,  and  is 
ready  for  use. 

IMolds  for  plain  teeth  differ  from  those  for  gum-section  teeth  in  that 
those  for  the  anterior  teeth  and  the  molar  and  bicuspid  teeth  are  made 
separate.  The  anterior  mold,  however,  as  will  be  seen  in  Figs.  126 
and  127,  is  intended  for  two  sets  of  teeth  of  the  same  pattern. 

Molding  and  Burning  Porcelain  Teeth. — The  first  step  in  molding  is  to 
oil  the  brass  mold  and  put  the  platinum  pins  in  the  small  holes  drilled 


182 


PORC'ELAiy   TKKTIL 


for  their  reception  in  tlie  pin  side  of  the  molds.  The  point  enamel  is 
then  put  in  the  face  side  of  the  mold,  and  arranged  with  a  small  spatula 
to  the  full  thickness  at  the  point  and  tapered  down  sparingly  toward  the 


Fig.  128 


Face  side  of  bicuspid  and  molar  mold. 


neck.  A  thin  coat  of  point  enamel  is  placed  on  the  lingual  side  of  the 
front  teeth  and  on  the  masticating  surfaces  of  the  bicuspids  and  molars. 
The  mold  is  then  laid  aside  to  dry  before  placing  the  gum  enamel  in 


Fig.  129 


Mold  for  bicuspid  and  molar  plain  rubber  teeth  with  crown  pieces  and  key  in  position. 

place.  Some  makers  of  teeth  use  Init  one  enamel ;  instead  of  applying  a 
yelloW'  neck  enamel,  they  allow  the  body  to  show  at  the  neck  of  the 
tooth;  this  is  probably  done  to  save  time  and  labor,  but  it  does  not 
afford  the  best  results  as  to  translucency  and  natural  appearance. 


THE  PROCESS  OF  MANUFACTURE  OF  PORCELAIN  TEETH.   183 

The  gum  enamel  is  mixed  with  water  and  made  just  stiff  enough  to 
stay  where  it  is  phiced  by  the  enamel  spatula,  and  is  then  spread  evenly 
over  the  gum  surface  of  the  mold,  the  thickness  being  ascertained  hy 
touching  the  point  of  the  spatula  to  the  mold  at  every  eighth  of  an  inch. 
The  placing  of  the  enamel  requires  more  experience  than  does  any  other 
part  of  the  molding  process.  The  gum  enamel  must  be  placed  close 
to  the  necks  of  the  teeth,  but  must  not  be  allowed  to  impinge  upon  the 
crowns;  when  complete  it  is  allowed  to  dry  partially. 

The  body  is  applied  in  small  pieces  slightly  in  excess  of  the  quantity 
needed  for  each  block.  These  are  taken  up  with  a  small  spatula,  formed 
into  balls,  and  laid  on  the  pins  in  the  pin  side  of  the  mold.  The  two 
sides  of  the  mold  are  then  placed  quickly  together,  put  under  the  press, 
and  the  lever  applied  to  force  the  two  parts  of  the  mold  together.  The 
mold  is  then  taken  from  the  press,  put  in  an  iron  clamp,  and  screwed 
firmly  together;  it  is  then  heated  until  the  mold  becomes  hissing  hot, 
when  it  is  allowed  to  cool  sufficiently  to  handle.  The  clamp  is  then  re- 
moved, the  mold  opened,  and  the  block  made  to  drop  out  by  striking 
the  mold  with  a  wooden  mallet. 


Fig.  130 


Crown  pieces  and  key. 

If  the  heating  has  been  carried  to  the  proper  point,  the  blocks  will  be 
found  hard  enough  through  the  agency  of  the  starch — which,  it  will  be 
remembered,  is  an  ingredient  in  the  formulas  for  bodies  for  molded 
teeth — to  admit  of  trimming;  this  is  done  with  small  files  and  separating 
saws.  After  trimming,  the  blocks  are  laid  aside  in  complete  sets  for 
burning. 

Burning. — In  manufacturing  on  a  large  scale  the  blocks  are  arranged 
in  complete  sets  on  a  fire-clay  slide  covered  with  coarse  quartz.  These 
slides  are  6^  inches  in  width  by  9j  inches  in  length;  they  have  raised 
edges  to  retain  the  quartz  which  serves  as  a  bed  for  the  blocks;  they 
hold  from  twelve  to  fifteen  sets,  according  to  the  size  of  the  blocks. 

The  furnaces  used  by  the  large  manufacturers  have  a  capacity  of 
three  or  four  hundred  sets  per  day  for  one  furnace  (Fig.  131).  These 
furnaces  are  square,  with  a  heating  oven  directly  over  the  fire,  the 
muffle  being  placed  lower  down;  the  furnace  is  connected  with  the 
smokestack  by  flues  at  the  top.  The  muffles  are  constructed  of  the 
best  prepared  fire-clay,  27  inches  long,  8  inches  wide,  5|  inches  high. 


184 


PORCELAIN  TEETH. 


and  1  ',  inches  thick.  The  inufHe  ninst  be  thoroughly  swahhed  with 
chiy  mixed  thin  with  water,  to  fill  iij)  all  cracks  or  defects  through 
which  the  gases  from  tlie  fuel  might  enter  the  muffle.  Such  accidents 
are  of  fre(|uent  occurrence  in  l)urning,  and  are  always  ruinous  to  the 
teeth,  the  gas  generally  imparting  to  them  a  ghastly  blue  appearance. 

As  it  is  necessary  to  cool  the  blocks  very  grachially  after  burning  to 
prevent  cracking,  they  are  placed  in  cooling  muffles  or  ovens  made  of 
flat  pieces  of  fire-brick  about  12  inches  s(|uare.  These  are  l)uilt  in  tiers 
of  ten  in  each  row;  each  oven  is  provided  with  a  loose  flre-bri(  k  stopper 


Revflaiion  ml  furnace  used  for  b:ikiii_'  ])iiri(l,iin  n-fth. 

The  slide  containing  the  teeth  is  placed  in  the  heating  imiffle  at  the  top 
of  the  furnace  before  burning;  this  preliminary  heating  prepares  them 
for  the  higher  temperature  of  the  muffle,  into  which  they  are  lifted  on  a 
flat  iron  shovel;  the  door  is  then  closed.  The  length  of  time  refpiired 
for  burning  the  blwlcs  on  each  slide  varies  according  to  the  heat  of  the 
muffle;  about  fifteen  minutes  is  allowed  each  slide.  A  too  rapid  heat 
tends  to  burn  out  or  vaporize  the  colors  of  the  enamels.  The  proper 
glazing  of  the  teeth  is  ascertained  by  placing  them  under  a  gas  jet. 


CLASSES   OF  FORCE  LAIN  TEETH. 


185 


The  ap})earance  of  this  glaze  is  difficult  to  describe  and  must  he  seen  to 
be  appreciated;  when  once  intelligently  observed  it  will  always  be  recog- 
nizable. When  the  final  burning  is  satisfactorily  accomplished,  they  are 
put  in  the  cooling  muffle,  protected  from  the  air  by  a  door  or  stopper,  and 
left  undisturbed  until  quite  cold. 


CLASSES  OF  PORCELAIN  TEETH. 

Porcelain  teeth  may  be  divided  into  two  general  classes,  namely,  gum 
and  plain  teeth.  In  the  former  the  labial  or  buccal  portions  of  the  gum 
about  the  teeth  are  represented  by  porcelain  which  is  colored  to  imi- 
tate the  mucous  membrane,  while  the  latter  represent  only  the  crowns 
of  the  teeth.  The  base  upon  which  they  are  to  be  mounted  and  the 
means  of  attachment  to  the  base  further  divide  them  into  classes  as 
follows : 


Gum  teeth.   < 


Gum  section  or  block  teeth  (for  vulcanite  work)  (Fig.  132). 

C  Gum  plate  teeth  (Figs.  133  and  134). 
Single  gum  teeth  -;  Single  gum  teeth  (for  vulcanite  work)  (Figs.  135 

(     and  136). 


Plain  teeth 
(single). 


Plain  rubber  teeth  (Fig.  137). 
Countersunk  pin  teeth  (Fig.  138). 
Diatoric  or  pinless  teeth  (Figs.  139  and  140). 
^  Plain  plate  teeth  (Figs.  141,  142,  143,  144,  and  145). 
Saddle-back  teeth  (Figs.  146  and  147). 
Continuous-gum  teeth  (Fig.  148) . 
English  tube  teeth  (Figs.  149,  150,  and  151). 

Fig.  132 


Gum  section  teeth,  upper  and  lower. 
Fig.  133  Fig.    134 


Single  gum  plate  teeth. 


186 


PORCELAIN  TEETH. 


Fig.  135 


Fig.  136 


Single  gum  teeth  for  vulcanite  work. 
Fio.  137 


Plain  rubber  teeth,  upper  and  lower. 
Fig.   138 


'    \ 


m  #1 


y(i^(><i) 


f^  f^  f^ 


TAl 


H  r^^'! 

p 


Countersunk  pin  teeth 


Fiu.  139 


Fig.   140 


Diatoric  or  pinless  teeth,  upper  and  lower  molars  and  bicuspids. 
Fig.    141  Fig.  142  Fig.  143 


Plain  plate  teeth,  incisors  and  canines 


CLASSES  OF  PORCELAIN  TEETH. 


187 


Fig.  144 


Fig.  145 


Fig.  147 


J 

i 


Plain  plate  teeth,  bicuspids  and  molars. 
Fig.  146 

I'll 

Saddle-back  teeth,  upper  and  lower  molars,  and  bicuspids 
Fig.   148 


Continuous-gum  teeth,  incisor  and  bicuspid. 


Fig    149 

Incisors. 

Defective.     Improved. 


Side.  Side. 


Plan. 


Plan. 


Fig.  150 
Bicuspid. 


Front. 


Side. 


Plan. 
English  tube  teeth. 


Fig.  1.51 

Molar. 


Front. 


Side. 


The  means  by  which  the  porcelain  teeth  are  attached  to  the  base 
plate  upon  which  they  are  mounted,  is  usually  two  platinum  pins,  the 
headed  ends  of  which  are  embedded  in  the  substance  of  the  teeth  and 
firmly  fixed  in  it  when  the  porcelain  is  baked.  ■  Platinum  and  porce- 
lain have  very  nearly  the  same  coefficient  of  expansion,  so  that  m  a 
similar  range  of  temperature  they  approximately  expand  and  contract 
alike,  and  there  is  small  danger  of  a  cracking  of  the  tooth  or  a  loosening 


188 


PORCELAiy    TKKTII. 


Fig.  152 


of  the  pin.  It  must  l^e  remembered,  however,  that  the  capacity  for 
absorbint^  heat  (hfi'ers  greatly  with  the  two  substances,  platinum  having 
a  much  higher  specific  heat,  which  fact,  coupled  witii  its  greater  con- 
ductivity, makes  it  necessary  that  a  greater  amount  of  heat  should  be 
applied  to  the  porcelain  when  teeth  are  subjected  to  high  heat.  The 
platinum  does  not  fuse  at  the  high  temperature  necessary  to  the  baking 
of  the  body  of  the  tooth,  and  its  non-oxidizable  surface  makes  it  possi- 
ble for  the  porcelain  to  adhere  to  it  with  consi(lera])le  tenacity.  One 
manufacturer  alloys  iridium  in  small  amount  with  the  platinum  to  give 
the  pins  greater  rigidity  and  tensile  strength. 

The  great  cost  of  platinum  has  been  responsible  for  many  attempts 
either  to  substitute  other  and  less  expensive  metals  for  it,  or  to  reduce 
the  amount  of  metal  used  for  the  attachment  in 
the  tooth,  or  to  dispense  with  the  pins  altogether. 
The  less  expensive  metal  usually  employed  is 
nickel  or  some  of  its  alloys,  but  as  these  readily 
oxidize  during  the  baking,  the  intimacy  of  the 
union  between  pin  and  tooth  cannot  be  so  close 
as  where  platinum  is  used.  The  discoloration 
of  the  tooth  from  the  dissolved  oxides  of  the 
pins  is  frequently  sufficient  in  amount  to  be 
objectionable,  and  the  low  fusing  body  which  is 
necessary  with  teeth  of  this  sort  is  not  so  strong 
as  that  which  may  be  baked  on  platinum  pins. 
The  attachment  of  pins  of  base  metal  to  plati- 
num anchorage  baked  in  the  tooth  by  soldering 
the  pin  to  the  anchorage  is  an  ingenious  method 
adopted  by  one  manufacturer  to  reduce  the 
amount  of  platinum  (Fig.  152).  The  anchorage 
is  in  the  form  of  a  tube  embedded  in  the  por- 
celain, the  inner  end  of  which  is  expanded  into  a  flange  which  is  for  firm 
retention.  The  pins  of  alloy  are  made  to  fit  the  tubes  and  are  soldered 
to  them  wath  high  grade  solder,  and  tests  seem  to  have  proven  that  the 
teeth  are  strong  enough  for  satisfactory  service. 

The  construction  of  teeth  whose  attachment  is  by  means  of  an  under- 
cut recess  in  the  tooth  filled  with  the  plastic  base  upon  which  they  are 
mounted  is  another  attempt  to  reduce  the  cost  of  production  by  doing 
away  with  the  platinum  entirely.  They  are  called  "pinless"  or  "diatoric 
teeth  "  (Fig.  153).  The  mechanical  difficulties  in  the  construction  of  a 
tooth  of  this  type,  which  shall  be  sufficiently  strong,  have  limited  their 
use  practically  to  the  bicuspids  and  molars,  in  which  positions  under 
favorable  conditions  they  are  eminently  satisfactory.  It  must  be  remem- 
bered that  as  their  strength  depends  upon  the  bulk  of  j)<)rcelain  com- 
posing them,  and  that  as  this  is  U\ss  than  in  })in  teeth,  it  is  not  possible 
to  make  more  than  minor  changes  in  them  by  grinding. 

Gum  teeth  are  made  for  metal  plates  and  for  the  plastic  bases,  those 
for  the  former  being  at  this  time  made  only  as  single  teeth  (Figs.  133  and 
134),  while  those  for  the  latter  are  usually  in  sections  of  two  or  more 
teeth  and  designated  "  gum  section  "  or  "  block  "  teeth  (Figs.  132  and  1 54- 


o,  Base  metal  pin ; 
platinum  ancborage  ; 
expanded  end  of  same 


CLASSES  OF   PORCELAIN  TEETH. 


189 


loO).  The  use  of  gum  teetli  is  limited  to  those  eases  in  which  resorp- 
tion of  the  alveohvr  process  has  taken  place  to  such  an  extent  as  to 
demand  considerable  restoration  by  means  of  the  denture.  With  the 
exception  of  that  found  in  continuous-gum  dentures  the  porcelain  of 
gum  teeth  provides  the  best  imitation  of  the  natural  tissues  which  has 
been  obtained,  but  tlie  fixedness  of  the  relation  between  the  teeth  in 
the  sections,  and  the  difficidty  of  joining,  particularly  of  the  single  gum 
teeth,  are  drawbacks  which  this  does  not  overbalance.  The  artistic 
'possibilities  in  arrangement  which  plain  teeth  offer  have  caused  them 
to  come  into  general  use,  and  in  most  cases  they  are  to  be  preferred. 
It  must  be  remembered,  however,  that  in  some  full  dentures,  and  many 


Fig.  153 


B  C 

Plan  of  diatoric  bicuspid  and  molar. 


Tig.  151 


Fig.  155 


Fig.  156 


Fig.  157 


Fig.  158 


Fig.   159 


,A'-> 


Gum  sections  for  partial  cases. 


partial  ones,  gum  teeth  may  be  used  to  great  advantage.    They  are  made 
in  a  variety  of  forms  and  offer  a  wide  selection  (Fig.?.  154  to  159). 

The  forms  of  porcelain  teeth  ase  determined  by  three  factors.  The 
most  important  of  these  is  the  anatomical  characteristics  of  the  teeth 
they  are  to  substitute.  As  only  the  crown  is  represented,  the  labial  or 
buccal  surfaces,  the  morsal  surfaces,  a.nd  such  portions  of  the  approximal 
surfaces  as  are  presented  to  view  are  patterned  after  the  natural  teeth. 
Teeth  c^uite  satisfactory  in  this  respect  are  manufactured  to-day,  although 
the  market  contains  many  made  according  to  old  designs  which  are  poor 
imitations  of  the  natural  organs.  The  form  of  the  incisors  and  cuspids 
is  in  general  much  better  than  that  of  the  molars  and  bicuspids,  the 
occlusal  surfaces  of  many  of  which  are  too  narrow  for  the  best  masti- 


190 


PORCELAIN  TEETH, 


catoiy  results,  the  cusps  are  too  poorly  defiuod,  and  no  attempt  is  made 
to  have  those  of  opposing  sets  fit  together. 

The  sha})e  of  the  other  ])()rtions  of  the  teeth  is  determined  by  con- 
siderations reUitive  to  their  attacliment  to  the  l)ase  u])on  which  they  are 
mounted,  and  by  the  mechanical  re(|uirements  which  the  shape  and 
relation  of  the  jaws  impose.  Teeth  for  vidcanite  and  celluloid  work  are 
similar  in  design  (Figs.  lOO  to  169).  WTien  the  latter  came  into  use 
the  artistic  ])()ssibllities  of  die  new^  material  created  a  demand  for  more 
natural  forms  of  teethe  and  so-called  "  celluloid  "  teeth  were  designed 


Fig.  160 


Fig.  161 


Fig.  162 


Fig.    163 


Fig.  164 


FiQ.  165 


Plain  rubber  teeth,  upper  and  lower  incisors,  and  cuspids. 


Fig.  166 


Fig.  167 


V\G.   168 


Fig.  169 


Plain  rubber  teeth,  upper  and  lower  bicuspids,  and  molars. 


to  meet  it.     Teeth  of  this  form  may  also  be  used  with  a  cast-metal  base, 
but  they  are  all  designated  rubber  teeth. 

Plain  rubber  teeth  are  provided  with  two-headed  pins  to  secure  their 
attachment  to  the  vulcanite.  In  the  incisors  and  cuspids  there  is  the 
so-called  "  pin  "  guard  situated  between  the  pins  and  the  morsal  edge 
to  afford  a  shoulder  to  which  the  vulcanite  may  be  finished. 


CLASSES   OF  POIiCELAiy   TKF.TH.  191 

Countersunk  pin  teeth  were  introduced  about  1885.  Their  hngual 
surface  corresponds  in  shape  to  that  of  the  natural  teeth,  the  attaclinient 
to  the  molded  base  being  by  means  of  pins  located  in  a  (lc])ression  in 
their  base.  Their  close  conformity  in  contour  to  the  natural  organs 
makes  them  more  acceptable  to  the  tongue  than  teeth  backed  in  the 
ordinary  way,  and  renders  articulation  easier  and  more  distinct. 

Inasmuch  as  they  must  be  mounted  almost  over  the  alveolar  ridge, 
they  cannot  be  used  in  cases  with  a  short  bite. 

Plain  plate  teeth  are  designed  for  use  on  a  metal  plate  or  in  crown 
and  bridge-work.  The  incisors  and  cuspids,  in  either  instance,  are 
similar  in  form  (Figs.  137  to  139),  but  those  for  use  in  the  bicuspid 
and  molar  region  for  crown  and  bridge-work  represent  only  the  buccal 
surface  of  the  tooth,  and  are  sometimes  known  as  "  veneers  "  (Fig.  170). 

Two  pins  project  from  the  flat  back  of  the  tooth  to  afford  attachment 
to  the  metal  backing  which  is  brought  into  contact  with  the  back  of  the 
tooth  for  its  support.     These  pins  are  arranged  crosswise  in  very  short 

Fig.  170 


Veneers  for  crown  and  bridge-work. 

teeth,  but  where  there  is  space  they  are  arranged  longitudinally  because 
of  the  greater  strength  thus  obtained. 

Saddle-back  teeth  (Figs.  146  and  147)  are  suitable  for  vulcanite 
dentures  in  which  the  space  between  the  jaws  posteriorly  is  very  slight 
and  where  it  would  not  be  possible  to  get  in  a  plain  rubber  tooth.  They 
may  also  be  used  for  bridge-work. 

Continuous-gum  teeth  are  illustrated  in  Fig.  148.  It  will  be  seen 
that  they  have  only  one  long  pin,  and  that  the  buccal  and  labial  portions 
of  their  roots  are  represented  in  porcelain.  This  contributes  to  the 
firmness  of  their  attachment  to  the  base,  the  porcelain  body  fusing  upon 
the  roots  and  uniting  them  to  the  plate.  It  also  maintains  the  contours 
of  these  regions  by  reducing  the  amount  of  porcelain  body  to  be  baked, 
and  hence  the  contraction  in  this  locality. 

English  tube  teeth  (Fig.  145  to  149)  are  little  used  in  this  country 
except  for  crowns,  but  they  are  more  or  less  extensively  employed  in 
England.  A  platinum  tube  baked  in  the  centre  of  the  tooth  affords 
lodgment  for  the  pin. which  attaches  them  to  the  plate  or  root. 


CHAPTER     IV. 

THE  HUMAxN  DENTAL  MECHANISM;     ITS  STRUCTURE, 
FUNCTIONS,  AND  RELATIONS. 

By  Charles  R.  Turner,  D.D.S.,  M.D. 

The  oral  cavity  is  situated  at  the  beginning  of  the  aHmentary  canal; 
it  serves  for  the  intake  of  food,  and  is  provided  with  the  means  of  its 
preparation  for  the  subsequent  stages  of  digestion  and  for  assimilation. 
In  the  production  of  articulate  speech,  it  serves  as  a  resonating  chamber 
for  the  vowel  tones,  and  by  alterations  in  its  shape,  through  the  action  of 
the  muscles  of  the  tongue,  lips,  cheeks,  and  palate,  it  determines  the  char- 
acter of  the  consonant  sounds.  The  face  is  the  principal  seat  of  the 
expression  of  emotions  in  man,  and  as  the  mouth  is  one  of  its  most  mobile 
features,  it  participates  prominently  in  the  performance  of  this  function. 
The  loss  of  the  teeth  and  the  changes  in  the  surrounding  tissues  which 
result  therefrom  arefollowedby  an  interference  with  the  functions  above 
enumerated,  and  by  alterations  of  facial  contour  which  greatly  affect  the 
personal  appearance  of  their  losers.  As  it  is  the  purpose  of  dental 
prosthesis  to  prevent  or  remedy  these  changes,  as  far  as  possible,  by  the 
substitution  of  artificial  apparatus  for  the  lost  tissues,  a  knowledge  of 
the  normal  operation  of  the  several  functions  thus  affected  is  of  fun- 
damental importance  to  the  study  of  the  subject.  This  chapter  aims, 
therefore,  to  treat  of  the  functions  of  the  dental  mechanism  from  this 
point  of  view.  It  will  discuss  the  manner  in  which  they  are  affected 
by  the  loss  of  the  teeth,  so  that  the  problems  arising  in  tooth  replace- 
ment may  be  solved  the  more  satisfactorily. 

The  most  important  function  of  the  mouth,  from  the  standpoint  of 
the  body  economy,  is  the  preparation  of  food  for  the  subsequent  stages 
of  digestion.  Food  stuffs  of  various  degrees  of  physical  consistence 
are  introduced  into  the  cavity,  their  solid  portions  are  cut,  crushed 
or  ground,  mixed  with  the  saliva,  and  are  then  carried  into  the  stomach. 
As  this  is  largely  a  mechanical  process,  we  shall  first  take  an  analytical 
view  of  the  mechanism  by  which  it  is  accomplished. 

THE  HUMAN  DENTAL  MECHANISM. 

Architecturally  considered,  the  masticating  mechanism  consists  of  a 
fixed  base,  the  upper  jaw,  supporting  the  upper  teeth,  against  which  is 
operated  a  movable  arm,  the  lower  jaw,  also  equipped  with  teeth  so 
placed  as  to  oppose  those  of  the  upper  jaw.  The  teeth  serve  as  the 
armament  of  the  apparatus,  affording  hard  surfaces  between  which  the 
food  is  crushed.  Muscles  extending  between  the  fixed  and  movable 
elements  of  the  apparatus,  and  so  disposed  as  to  be  capable  of  exerting 

192 


THE  FIXED  BASE. 


193 


great  pressure  in  approximating  them,  furnish  the  active  forces  of  the 
mechanism;  while  the  walls  of  the  buccal  cavity,  which  contains  the 
apparatus,  serve  to  confine  the  food,  and  the  lips  and  cheeks  together 
with  the  tongue  further  assist  the  process  by  keeping  it  between  the  crush- 
ing surfaces. 

The  Fixed  Base. — The  axial  skeleton  of  the  body  consists  of  the  ver- 
tebral column,  the  skeletal  basis  of  the  trunk,  which  supports  upon  its 
upper  extremity,  the  skull.  The  cranial  portion  of  the  skull  receives 
direct  support  at  the  atlo-occipital  articulation,  the  facial  portion  being 
in  turn  suspended  from  the  anterior  surface  of  the  cranium.  The  superior 
maxilla?,  united  in  the  median  line  and  lodging  the  upper  teeth, are  sup- 
ported upon  the  cranium  through  articulations  by  the  frontal,  lachry- 
mal, ethmoid,  palate,  vomer,  and  malar  bones,  and  constitute  the  fixed 
base  of  the  masticating  mechanism. 


Fig.   171 

k 

9 

i^B 

'  ^flB 

■^H 

^H 

^wl 

I'P 

M  ^^|H 

H| 

J/ 

.1 

^j^MMHH^^^Hj^^H 

j^M 

SS( 

jUi 

m    ' 

c 

4t. 

P                  3>r-' 

1 

Architectural  construction  of  skeletal  portion  of  masticating  apparatus:  the  fixed  base,  and 
moveable  arm.  Columns,  arches,  and  buttresses  of  the  fixed  base;  fronto-nasal  column,  A  B; 
zygomatic  column,  C  M  D;  pterygoid  column  (only  partly  visible),  supra-orbital  arch,  B  F  D; 
infra-orbital  arch,  BID;  upper  nasal  half  arch,  B  G;  palatal  arch  (not  shown);  lower  nasal  arch, 
A  H;  large  molar  arch,  A  C;  molar  buttresses  (descending  from  M);  pterygoid  arches  (not  shown). 
Columns  and  arches  of  the  moveable  arm;  mental  column,  N  K;  coronoid  column,  P  Q  O;  and 
condyloid  column,  J  L;  external  oblique  column,  Q  N.  (From  a  photograph  of  specimen 
No,  4237,  Wistar  Institute  of  Anatomy.) 


The  arch  shaped  alveolar  process  (Fig.  171),  containing  the  teeth 
which  receive  the  impact  of  mastication,  is  supported  upon  the  cranium 
by  three  pairs  of  columns  or  buttresses,  reinforced  by  several  secondary 
arches  and  braces.  (Burchard.)  The  columns  are  the  fronto-nasal,  as- 
cending from  the  position  of  the  canine  tooth  to  the  inner  margin  of 
the  orbit,  and  reaching  the  frontal  bone;  the  zygomatic,  extending  from 

13 


194 


THE  HUMAN  DENTAL  MECHANISM. 


the  position  of  the  first  molar  tooth  through  the  outer  margin  of  the 
orbit;  and  the  pterygoid,  ascending  from  the  molar  region  upward  and 
backward  to  the  sphenoid.  These  columns  are  strengthened  by  braces 
as  follows:  the  supra-orbital  arch,  the  infra-orbital  arch,  the  upj)er  nasal 
half  arches,  the  palatal  arch,  the  lower  nasal  half  arches,  the  large 
molar  arch,  the  molar  buttresses,  and  the  pterygoid  arches.  It  will 
be  noted  that  the  articulations  of  the  maxilhie,  notably  those  with  the 
malar  bones,  are  disposed  to  resist  stress  operating  from  below.  This 
fixed  base  is  admirably  constructed  to  receive,  resist  and  dissipate 
force  received  from  below  so  that  the  brain  and  delicate  sense  organs 
contained  in  the  face  will  not  be  unduly  shocked  during  mastication, 
and  is  "erected  to  endure  the  shock  of  impact  from  all  sorts  of  biting, 
i.e.,  cutting,  tearing,  crushing,  triturating  with  longitudinal  and  trans- 
verse motions,  and  to  resist  and  stand  firm  during  all  the  varieties  of 
movements  incident  to  mastication." 


Fig.    172 


The  lower  jaw  as  a  lever  of  the  third  class.      (Burchard.) 

The  Movable  Arm. — The  lower  jaw  consists  of  an  arch-shaped 
horizontal  portion,  the  body,  which  supports  the  lower  teeth  by  means  of 
its  alveolar  process,  and  terminates  posteriorly  in  two  vertical  branches, 
the  rami,  by  which  it  articulates  with  the  cranium.  It  may  be  re- 
garded mechanically  as  a  lever  of  the  third  class  (Fig.  172),  the  fulcrum 
being  located  at  the  temporo-mandil)ular  joint,  the  power  being  repre- 
sented by  the  levator  muscles,  while  the  weight  consists  in  the  resistance 
to  the  elevation  of  the  jaw  offered  by  the  food  between  the  teeth. 

The  muscular  apparatus  by  which  the  jaw  is  raised  is  attached  in 
part  to  the  cranium  and  in  part  to  the  strong  zygomatic  arch,  and  is 
not  concentrated  upon  one  point  on  the  mandible,  but  its  attachment 
thereto  is  distributed  between  the  fulcrum  and  the  weight.  The  resultant 
line  of  its  action  when  the  teeth  are  in  contact  passes  sliglitly  behind 
the  coronoid  process  of  the  mandible  and  approximately  through  its 
anatomical  angle.  (Fig.  173,  M.)  The  lever  is  bent  at  this  point  so  that 
the  general  plane  of  the  teeth  wdien  in  occlusion  is  perpendicular  to  tlie 
line  of  action  of  the  levators.  By  this  arrangement  the  teeth  may  best 
oppose  the  action  of  the  levators,  since  they  resist  force  best  which  acts 


THE  MOVEABLE  ARM. 


195 


at  a  right  antrle  with  the  general  plane  of  their  occlusal  surfaces.  The 
resistance  offered  by  the  food  between  the  teeth  (which  represents  the 
weight)  varies  for  any  given  food  with  its  position  on  the  teeth.  For  a 
food  of  given  resistance  the  farther  back  in  the  mouth  it  is  placed,  the 
nearer  it  is  to  the  fulcrum,  and  the  shorter  the  weight-arm  of  the  lever, 
and  hence  the  less  will  be  the  muscular  force  necessary  to  overcome  the 
resistance. 

The  point  of  the  origin  and  insertion  of  the  muscles  is  fixed,  but  as 
the  position  of  the  fulcrum  changes  in  its  relation  to  the  former  of  these 
during  the  movements  of  the  jaw,  the  length  of  the  power-arm  of  the  lever 
is  affected,  and  the  resistance  which  may  be  overcome  by  the  muscles 
varies  in  accordance  therewith.  The  more  nearly  the  jaws  are  together 


Fig.   173 


Diagram  illustrating  line  of  action  of  levators  of  lower  jaw. 

the  longer  is  the  power-arm,  and  hence  it  will  be  found  that  the  more 
nearly  they  are  approximated,  the  greater  will  be  the  power  which  the 
muscles  may  exert.  From  these  several  facts  it  will  be  seen  that  the 
lever  is  of  the  type  best  suited  to  the  lifting  of  a  heavy  weight  slowly 
through  a  short  distance. 

To  resist  the  stress  put  upon  it  in  these  operations  the  jaw  is  well  de- 
signed structurally.  (Fig.  171.)  It  may  be  considered  as  composed  of 
several  pairs  of  bony  columns.  The  vertical  columns  are  the  mental 
column,  extending  perpendicularly  upward  from  the  lower  margin  of 
the  body  to  the  position  of  the  canine  tooth,  the  coronoid,  ending  in 
the  coroiioid  process,  and  the  condyloid  parallel  to  it  and  ending  in  the 
condyle.     These  are  bound  together  by  the  long  body  columns  of  the 


HjQ  THE  HUMAN  DENTAL  MECHANISM. 

external  and  internal  oblique  lines.  Cryer'  has  pointed  out  the  archl 
tectural  strenjjjth  of  the  body  of  the  bone,  the  cortical  U-shaped  por- 
tion of  the  exterior  being  bound  together  by  the  internal  cancellated 
tissue. 

The  fulcrum  of  the  lever  rests  upon  the  base  of  the  skull  where  the 
bone  is  thick  and  dense  and  well  dcsi(2;ned  to  resist  the  force  put  upon 
it,  and  the  joint  itself  is  provided  with  intervening  soft  tissues  as  a 
means  of  lessening  the  shock  of  activity. 

The  Temporo-Mandibular  Articulation. — This  is  a  condylarthrodial 
joint,  the  structures  taking  part  in  it  being  the  glenoid  fossa  of  the  tem- 
poral bone  and  the  condyle  of  the  lower  jaw,  together  with  the  proper 
and  accessory  ligaments,  and  the  tissues  interposed  between  the  bones. 

The  Glenoid  Fossa. — This  is  an  ol)long  cavity  (Fig.  174)  on  the  under 


Flc  174 


Left  glenoid  fossae  of  four  skulls,  showing  differences  in  form. 

surface  of  the  squamous  portion  of  the  temporal  bone,  its  concavity  being 
directed  downward.  It  is  bounded  anteriorly,  by  the  eminentia  articu- 
laris  (the  anterior  root  of  the  zygoma),  externally,  by  the  middle  root  of 
the  zygoma  and  the  auditory  process,  and  posteriorly,  by  the  tympanic 
plate  of  the  petrous  portion  of  this  bone.  The  Glaserian  fissure  which 
runs  across  the  cavity  divides  it  into  two  unequal  portions,  the  posterior 
third  being  rough  and  lodging  a  portion  of  the  parotid  gland,  the  anterior 
two-thirds  being  smooth  and  covered  in  the  recent  state  with  a  dense 
fibrous  tissue  and  receiving  the  condyle  of  the  lower  jaw.  Of  the 
articular  portion  of  the  fossa  the  distal  part  is  the  most  concave  and 
is  also  the  most  elevated.  From  this  point  it  slopes  downward  and 
forward  to  the  crest  of  the  eminentia  articularis,  furnishing  a  surface 
over  which  the  condyle  glides  in  the  forward  excursions  of  the  mandible. 
The  shape  of  the  cavity  varies  with  different  nationalities,  with  different 
individuals,  and  sometimes  on  both  sides  of  the  same  individual. 
The  principal  variations  are  (1)  in  size  and  general  concavity,  in  corres- 
pondence wath  the  shape  of  the  condyle;  (2)  in  extent  of  surface  from  the 
most  concave  portion  to  the  eminentia  articularis;  (3)  in  its  inclination. 

^  Internal  Anatomy  of  the  Face. 


THE  GLENOID  FOSSA. 


197 


The  outlines  in  Fig.  175  show  the  curve  of  this  cavity  obtained  fnnn 
skulls  after  the  method  of  Tomes  and  Dolamore.  The  fossa  alters 
frequently  in  old  a<ije  from  the  {)ull  of  the  muscles  upon  the  mandible 
in  trying  to  bring  into  occlusion  teeth  that  may  be  widely  separated 
in  location. 

The  condyle  of  the  lower  jaw  (Fig.  170),  is  the  upper  extremity  of  the 
ramus  which  fits  into  the  glenoid  fossa.  It  consists  of  the  neck  by 
which  it  is  joined  to  the  ramus,  and  the  head  which  is  ovoid  and 
oblong  in  shape  corresponding  to  the  fossa  into  which  it  fits.  Its 
long  axis  is  transverse,  and  if  extended  would  meet  that  of  the  other 
condyle  approximately  in  front  of  the  foramen  magnum,  while  its  short 
axis  prolonged  would  meet  that  of  its  fellow  approximately  at  the 
symphysis  mentis.  It  is  convex  from  before  backward  and  from  side  to 
side.     The  articular  surface  extends  to  a  Iowti  level  posteriorly  than 

Fig.   175 


Outlines  of  glenoid  fossse  obtained  by  the  method  of  Tomes  and  Dolamore,  The  heavy 
base  line  is  parallel  to  a  line  drawn  from  the  anterior  nasal  spine  to  the  floor  of  the 
external  auditory  meatus.  All  the  fossse  outlined  were  on  the  lett  side  of  the  skull.  A, 
from  skulls  with  typical  dentures ;  B  and  C  Irom  skulls  with  several  teeth  missing;  D  and 
E,  from  edentulous  skulls. 


anteriorly  to  permit  rotation  of  the  jaw  about  the  condyles.  The  artic- 
ular surface  of  the  condyle  may  be  said  to  present  two  faces,  an  upper 
or  anterior  and  a  lower  or  posterior,  the  division  between  them  not 
being  distinctly  marked.  It  is  covered  with  a  thin  covering  of  fibrous 
tissue  which  serves  to  even  up  its  surface  without  altering  its  shape. 

The  shape  of  the  condyle  and  the  fossa,  which  more  or  less  accurately 
correspond  in  size,  differs  greatly  in  different  individuals.  There  is 
a  definite  relation  between  the  shape  of  these  parts  and  the  movement  of 
which  the  lower  jaw  is  capable.  The  long  narrow  condyle  (Fig.  176,  D), 
characteristic  of  the  nervous  temperament,  is  received  into  a  groove- 
like fossa, and  permits  more  easily  the  up  and  down  motion  of  the  jaw, 
in  which  the  joint  acts  largely  as  a  hinge.  In  the  sanguine  tempera- 
ment (Fig.  176,  B),  the  condyle  is  more  rounded,  the  articulation  partak- 


108 


THE  HUMAN  DENTAL  MECHANISM. 


iiiif  more  of  tlio  natuiv  of  a  hall-aiid-socket-joiut,  the  lateral  excursion 
of  the  nmiulihle  l)eiii^  readily  accomplished.  In  the  bilious  tempera- 
ment the  condyle  (Fig.  17(),  C)  is  also  narrow  and  lonif,  while  in  the  lym- 
])hatic  {V\^.  17(),  A),  the  joint  favors  greatly  lateral  movement  and  the 
condyle  and  fossa  are  flattened  correspondingly. 

Interposed  between  the  head  of  the  condyle  and  the  fossa  and 
separated  from  each  by  a  synovial  sac  is  found  the  interarticular 
fibro-cartilage  (Fig.  177).  This  is  a  disk-like  cartilage  ovoid  in 
shape,  its  upper  surface  concavo-convex  from  before  backward  to 
correspond  to  the  shape  of  the  fossa.  It  is  concave  in  front  where 
it  comes  in  contact  with  the  eminentia  articularis,  and  convex  poster- 
iorly where  it  fits  into  the  concavity  of  the  fossa.     On  its  lower  surface 

Fig.     170 


■■ 

■i 

E^ 

^    ^B 

1^        i 

^■::J.    ^^m 

^^   m 

^m     ^H 

^^K'^  ^ 

^k'   ' 

Hr    ^V 

^v 

K.     I^H 

■V  i 

m^ 

^^^v~     ^  ^^^^^^1 

^mlw 

^^^H  '' 

^Ki-'  1 

|^:'^H 

^^^^K  ^ 

^^^B 

H^^^^^^r^               ^^1 

Hr^^  ^^^^1 

^^^^^^^  - 

^^^B 

^^^SL'/*:'            ^1 

wKFi'  '--fX^  .^^^^^9 

^^^K 

^HB     j 

^^^^B".^  ^1 

E^'J^^H 

^^^^^^^^|L-  '^l 

^E^        J 

^Hpr/  fl 

B^^^H 

Li 

HH 

A  B  C  D 

Left  condyles  of  four  mandibles,  showing  differences  in  form:  A,  partaking  of  the  characteristics 
of  the  lymphatic  temperament;  B,  partaking  of  the  characteristics  of  the  sanguine  temperament; 
C,  partaking  of  the  cliaractcristics  of  the  bilious  temperament ;  D,  partaking  of  the  character- 
istics of  the  nervous  temperament. 


it  is  concave.  The  posterior  border  is  nearly  twice  as  thick  as  the 
anterior,  while  the  external  border  is  thicker  than  the  internal.  In  the 
normal  resting  bite  the  cartilage  covers  only  the  upper  anterior  portion 
and  the  top  of  the  condyle  which  it  surmounts,  while  the  posterior 
aspect  of  the  articular  surface  of  the  condyle  is  not  in  contact  with  it, 
but  with  the  posterior  part  of  the  capsule.  In  the  excursion  of  the 
jaw  the  cartilage  and  condyle  leave  the  fossa  together  or  more  rarely 


Tilt:  I^TER ARTICULAR  FIBRO-CARTlLAClE. 


199 


the  condyle  ooes  forward  over  the  surface  of  the  cartihiffe.  The  disk 
is  attached  to  the  condyle  most  intimately  internally  and  externally, 
which  causes   the  cartilage  and   condyle  to  go  forward   toojether  and 


Fig.   177 


Vertical  section  through  head  passing  through  both  temporo-mandibular  articulations  and 
showing  on  the  left  side  of  illustration,  the  right  condyle,  cartilage,  and  fossa.  Looking  backward. 
(Cryer.) 


yet  does  not  prevent  a  rotation  of  the  jaw  about  the  condyles.  The 
contraction  of  the  external  pterygoid  muscle,  which  is  attached  to  the 
anterior  edge  of' the  cartilage,  is  equally  responsible  for  its  forward 
movement.  The  synovial  sacs  (Fig.  178)  above  and  below  the  disk, 
permit  the  gliding  and  rotating  movements  of  the  joint.  The  cartilage 
alwavs  furnishes  a  base  upon  which  rotation  takes  place  and  is  always 
interposed  between  the  condyle  and  the  fossa. 

The  ligaments  of  the  joint  (Figs.  179  and  180),  are  the  capsular,  the 
external  and  internal  lateral  ligaments,  which  are  only  thickenings  of 
the  capsular,  and  several  accessory  ligaments. 

The  capsular  ligament  is  attached  above  to  the  anterior  border  of 
the  root  of  the  zygoma,  behind  to  the  bottom  of  the  glenoid  cavity  a 
little  in  front  of  the  Glaserian  fissure,  on  the  outside  to  the  zygomatic 
tubercle  and  the  longitudinal  root  which  follows  it,  and  on  the  inside 
to  the  base  of  the  spine  of  the  sphenoid.     It  is  attached  below  around 


200 


THE  HUMAN  DENTAL  MECHANISM. 

FiQ.  178 


ERYGOIDEUS 
EXTERNUS 


Temporo-mandibular  articulation  in  sagittal  sections.     (Testut.) 


i^iMii^ 


Fig.  179 

B 

\ 

f^'^^^ 

t  A, 

li.**^              A^^ 

Ligaments  of  temporo-mandibular  joint:  (external  \-iew).     A,  capsular;      B,  external  laterai; 
C,  stylo-maxillary.  (Deaver.) 


THE  LIGAMENTS. 


201 


the  neck  of  the  condyle:  anteriorly,  immediately  below  the  articular 
surface,  posteriorly,  to  a  line  3-4  mm.  lower.  This  permits  the 
articular  surface  of  the  condyle  to  be  in  relation  with  the  cartilage 
duringany  of  its  normal  movements.  The  internal  surface  of  the  cap- 
sular ligament  is  intimately  connected  with  the  cartilage  around  its 
periphery  where  the  two  come  in  contact,  thus  dividing  the  cavitv  into 
two  portions. 

The  capsular  ligament  consists  mainly  of  vertical  fibers,  and  is  thin, 
particularly  in  front,  where  it  gives  attachment  to  some  fibers  of  the 


D     B 


Fig      180 


Ligaments  of  the  temporo-mandibular    joint    (internal  view):    A,  Long  internal  lateral  or  spheno- 
maxillary ;  B,  short  internal  lateral  ;  C,  stylo-maxillar\-.      (Deaver.) 

external  pterygoid  muscle.  Posteriorly  there  are  some  elastic  fibres 
attached  a  little  anterior  to  the  Glaserian  fissure,  and  passing  downward 
are  attached  to  the  cartilage  and  the  neck.  Sappey^  says  these  contri- 
bute to  limit  the  forward  displacement  of  the  cartilage  and  condyle  and 
serve  to  bring  the  former  back  when  the  mandible  retreats  into  the 
fossa. 

'  Traite  D'anatomie     Humaine.     Tcstut. 


202 


THE  HUMAN  DENTAL  MECHANISM. 


The  principal  suspensory  ligament  is  the  external  lateral,  which  is 
attached  above  to  the  outer  surface  of  the  zygoma  and  to  the  rough 
tubercle  on  its  lower  border,  and  below  to  the  outer  surface  and  pos- 
terior border  of  the  neck  of  the  condyle.  It  is  a  stout  thick  ligament, 
broader  above  than  below,  its  anterior  fibres  being  the  longer,  and  an- 
terior to  the  horizontal  axis  of  the  condyle.  By  reason  of  its  attach- 
ment it  assists  in  compelling  a  forward  movement  of  the  condyle  dur- 
ing depression  of  the  jaw. 

Fig.     181 


Temporal  muscle.    (Deaver.) 


The  internal  lateral  (or  short  internal  lateral),  is  shorter  than  the  ex- 
ternal, is  inserted  into  the  back  of  the  neck  of  the  condyle,  and  has 
longer  outer  fibres. 

The  spheno-maxillary  (or  long  internal  lateral  ligament)  is  attached 
to  the  alar  spine  of  the  sphenoid  anfl  extends  to  the  spine  on  the  man- 
dible internal  to  the  inferior  dental  foramen. 


THE  MUSCLES.  203 

The  stylo-maxillary  is  a  specialized  band  of  cervical  fascia,  extending 
f^om  the  styloid  process  to  the  ramus  a  little  above  the  angle  of  the  jaw. 
This  also  assists  in  compelling  a  forward  movement  of  the  condyle  in 
depression  of  the  jaw. 

It  will  be  noted  that  the  ligaments  of  the  joint,  while  permitting  great 
freedom  of  movement  in  certain  directions,  bind  the  condyle  firmly  in 
the  fossa,  and  that  the  groove-like  character  of  the  socket  limits  its  move- 
ment in  certain  directions.  Movement  distally  is  resisted  by  the  pos- 
.  terior  wall  of  the  cavity,  the  extent  of  compressibility  of  the  intervening 
soft  tissues  being  the  limit  of  movement  in  this  direction.  Movement 
forward  is  permitted,  as  we  have  seen.  Movement  outward  is  impossible 
and  movement  of  the  condyle  inward  is  possible  only  to  the  extent 
permitted  in  rotation  of  the  jaw  about  the  other  condyle.  Any  force 
tending  to  separate  the  contact  between  the  condyle,  cartilage,  and 
fossa  is  resisted  by  the  joint  ligaments  proper,  notably  the  external 
lateral,  so  that  such  movement  is  permitted  only  to  the  amount  to  which 
these  ligaments  may  be  stretched.  For  all  practical  purposes  the  condyle 
and  fossa  may  be  said  to  be  always  in  contact  through  the  medium  of 
the  interposed  cartilage,  for  the  reason  that  the  usual  forces  operating 
upon  the  jaw  tend  to  p^-ess  the  condyle  into  the  fossa  and  not  to  sepa- 
rate them.  In  edentulous  patients  where  the  fossae  are  very  flat,  the 
ligaments  seem  to  become  lengthened,  thus  permitting  a  large  range  of 
movement  to  the  jaw.  The  soft  tissues  interposed  between  the  bones 
are  slightly  compressible,  but  this  factor  is  so  small  in  amount  as  to 
be  practically  negligible  in  estimating  the  path  of  the  condyle  during 
the  movements  of  the  jaw.  Therefore  within  the  restriction  offered 
by  the  ligaments,  this  path  will  be  determined,  so  far  as  the  joint  is 
concerned,  almost  solely  by  the  form  of  the  glenoid  fossa.  Hence  it  will 
be  seen  that  there  is  a  definite  relationship  between  the  movements 
of  which  the  lower  jaw  is  capable  and  the  character  of  the  temporo- 
mandibular articulation. 

The  Muscles. — The  muscles  attached  to  the  lower  jaw  and  producing 
its  movements  are  the  temporal,  masseter,  external  and  internal  ptery- 
goids, ordinarily  classed  as  the  muscles  of  mastication  because  they  are 
the  active  forces  in  this  process,  together  with  the  mylo-hyoid,  the  genio- 
hyoid, the  digastric  and  the  platysma  myoides.  With  the  exception  of  the 
last  they  are  arranged  in  symmetrical  pairs  usually  operating  simul- 
taneously in  the  principal  movements  of  the  jaw,  although  each  is  capa- 
ble of  independent  contraction.  The  temporal  muscle  (Fig.  181),  the 
principal  levator  of  the  mandible,  arises  from  the  whole  of  the  temporal 
ridge  and  fossa  and  converges  to  be  inserted  into  the  coronoid  process. 
The  masseter,  short,  quadrilateral,  thick,  and  powerful  has  two  planes 
of  fibres,  the  external,  arising  from  the  malar  process  of  the  superior 
maxilla,  the  outer  surface  and  anterior  two  thirds  of  the  zygoma,  and 
inserted  into  the  lower  half  of  the  ramus  and  the  angle  of  the  jaw; 
the  internal  layer,  arising  from  posterior  third  of  the  zygoma  and 
attached  to  the  upper  portion  of  the  ramus.  The  internal  pterygoid  is 
also   thick  and   quadrangular  in  shape,  extending  from   the    ptery- 


204 


THE  HUMAN  DENTAL  MECHANISM. 


goid  fossa,  its  origin,  to  the  inner  surface  of  tlic  ramus  and  the 
angle  of  the  jaw.  The  external  pterygoid  arises  by  two  heads, 
one  from  tlie  under  surface  of  the  great  wing  of  the  sphenoid,  the 
other  from  the  tuberosity  of  the  maxillary  lione  and  the  palate  bone. 
The  fibres  pass  almost  horizontally  backward  and  outward  to  be  in- 
serted into  the  neck  of  the  condyle  and  the  anterior  margin  of  the  inter- 
articular  fibro-cartilage.  With  the  exception  of  the  last  described 
muscle  it  will  be  seen  from  their  points  of  attachment  that  they  serve 


Fig.  182 


Aledian  sagittal  section  of  head,  showing  relation  of  structures  in  oral  cavity    when    the    mouth 

is  closed.     (Cryer.) 


largely  to  elevate  the  mandible  into  contact  with  the  maxillae  by  rotating 
it  about  the  condyle.  They  arise  either  from  the  cranium  or  from  the 
strong  zygomatic  arch,  and  are  attached  to  the  lower  jaw  at  points  be- 
tween the  temporo-mandibular  articulation  and  the  teeth.  They  are 
short  and  powerful,  and  capable  of  exerting  considerable  force.  The 
function  of  the  external  pterygoids  acting  together  is  to  pull  the  condyle 
forward  and  downward  over  the  surface  of  the  glenoid  fossa,  and  to  so 
adjust  the  cartilage  that  it  is  always  interposed  between  the  condyle 
and  the  fossa.     The   external   pterygoid   on   either   side   contracting 


THE  MOVEMENTS  OF  THE  MANDIBLE.  205 

independently  of  its  fellow,  serves  to  pull  its  condyle  downward,  for- 
ward and  inward,  thus  rotating  the  jaw  about  the  opposite  condyle. 

The  depressor  muscles  are  mainly  attached  to  the  forward  end  of  the 
mandible.  The  genio-hyoid  and  the  anterior  belly  of  the  digastric  are 
inserted  into  its  inner  surface  near  the  median  line;  the  mylo-hyoid  being 
attached  to  the  ridge  of  that  name.  They  operate  from  the  hyoid  bone, 
which  must  first  be  fixed  by  the  omo-hyoid,  sterno-hyoid,  and  thyro- 
hyoid muscles.  The  platysma  myoides  is  attached  below  to  the  sternum 
'and  clavicle  as  its  fixed  base. 

Under  ordinary  conditions  when  the  mouth  is  closed  (Fig.  182),  the 
muscles  are  in  repose  and  there  is  an  absence  of  any  active  contraction 
on  their  part.  The  mandible  is  maintained  in  position  partly  by  the 
tonicity  of  the  levators,  their  length,  however,  in  an  ordinary  state 
being  too  great  to  keep  the  jaws  in  contact.  This  is  assisted  by  the  in- 
fluence of  a  certain  negative  intra-oral  air-pressure  amounting  to  about 
2-4  mm.  of  mercury  (Bonders)  which  "is  formed  by  the  contraction 
of  the  muscles  of  the  tongue  and  by  the  sinking  of  the  mandible.  The 
closed  space  arises  from  the  closure  of  the  lips,  and  the  placing  of  the 
soft  palate  upon  the  root  of  the  tongue."^  The  teeth  are  usually  in  con- 
tact at  some  point,  the  tongue  practically  fills  the  cavity  of  the  mouth, 
the  lips  and  the  cheeks  are  closely  applied  to  the  teeth  and  alveolar  pro- 
cess. This  position  is  commonly  termed  "the  resting  bite."  In  it  the 
teeth  do  not  fit  tightly  together,  the  cusps  not  being  closely  received  into 
their  corresponding  depressions,  the  condyles  are  distally  placed  in 
their  fossse,  and  the  levators  exhibit  only  ordinary  tone. 

If  the  levator  muscles  are  contracted  slightly,  the  jaw  is  drawn  upward 
and  backward  to  a  position  where  the  cusps  and  depressions  of  the  teeth 
do  correspond  and  we  have  a  more  closely  fitting  occlusion.  At  the 
same  time  the  condyles  are  occupying  their  most  distal  position  in  the 
fossae  and  we  have  what  is  called  "the  position  of  occlusion." 

If  the  levators  are  still  further  contracted  there  is  no  closer  fitting 
together  of  the  teeth,  but  they  are  forced  very  slightly  up  into  their 
sockets,  a  movement  permitted  by  the  elasticity  of  the  pericementum, 
while  at  the  same  time  the  interarticular  cartilage  and  other  soft  tissues 
intervening  at  the  joint  are  likewise  compressed  slightly.  It  is  the  lati- 
tude of  movement  between  the  position  of  occlusion  and  this  position 
which  reduces  the  shock  of  the  impact  of  the  mandible  during  masti- 
cation. 

The  Movements  of  the  Mandible. — Because  of  the  fact  that  it  has 
two  articulations,  the  movements  of  the  lower  jaw  are  so  complex  that 
it  will  be  best  for  our  purposes  to  describe  the  simple  movements,  and 
then  to  see  how  they  may  be  combined  to  produce  the  more  compli- 
cated ones.  Therefore  those  will  be  first  discussed  in  which  the 
symphysis  of  the  jaw  is  moved  in  the  sagittal  plane  of  the  body,  or 
in  other  words,  movements  which  are  bilaterally  symmetrical. 

Depression. — This  is  produced  by  the  weight  of  the  jaw  and  by  the 
action  of  the  mylo-hyoid,  genio-hyoid,  anterior  belly  of  digastric,  and 

'  E.  Herbst:   Deutschen   Zahnarzflichen  Wochenschrift. 


206 


THE  HUMAN  DENTAL  MECHANISM. 


the  platysma  myoides  muscles,  which  serve  to  depress  the  forward  end 
of  the  jaw,  and  by  the  action  of  the  external  pterygoid  muscles  which 
pull  the  heads  of  the  condyles  downward  and  forward.  The  jaw  rotates 
about  a  horizontal  axis  passing  through  the  condyles  which  at  the  same 
time  are  being  moved  downward  and  forward.  Sliding  is  thus  com- 
bined with  rotation  through  the  whole  movement  of  depression  of  jaw. 
(Fig.  183). 

Fig.  183 


Diai^ratn  illustrating  the  direction  of  operation  of  the  muscles  in  depressing  the  mandible 
R  C,  line  of  traction  of  external  pterygoid  muscles;  O  B,  line  of  traction  of  mylo-hyoid,  genio- 
hyoid and  digastric  muscles.     (After  Constant.) 

The  forward  movement  of  the  condyle  is  rendered  necessary  Vy  the 
attachment  of  the  external  lateral  ligament,  which  is  so  located  as  to  com- 
pel a  forward  movement  of  the  condyle  when  force  tending  to  displace 
the  jaw  downward  is  applied  at  its  anterior  portion.  It  is  also  produced 
by  the  contraction  of  the  external  pterygoid  muscle  which  likewise  pulls 
forward  the  cartilage  which  surmounts  it.  Man's  erect  posture  and 
the  forward  projection  of  the  larynx  necessitate  this.  The  path  which 
the  condyle  pursues,  downward  and  forward,  in  this  movement  is  de- 
pendent upon  the  shape  of  the  glenoid  fossa.  Walker^  found  it  to  make 
"an  angle  ranging  from  25°  to  45°  to  the  line  or  plane  of  occlusion,  being 
from  30°  to  50°  to  the  facial  line,"  the  average  of  the  former  being  35°, 
but  states  that  it  varies  very  much  even  on  both  sides  of  the  same  in- 
dividual. 

In  the  extreme  position  of  depression  of  which  the  jaw  is  capable  the 
condyle  is  in  the  lowest  and  most  anterior  position  which  it  ever 
assumes.  While  "the  mandible  describes  approximately  the  arc  of 
a  circle"  in  this  movement,  "no  portion  of  the  actual  path  is  coincident 
with  the  arc  of  a  circle  described  from,  as  its  centre,  any  position  ever 


1   The  Dental  Cosmos.  Vol.  xxxviii. ,   p.  34. 


ELEVATION. 


207 


attained  by  the  condjle."^  The  centre  is  generally  from  1  to  1^  inch 
below  the  level  of  the  condyle.  The  radius  of  the  circle  described  by  the 
morsal  edges  of  the  lower  incisor  teeth  may  vary  from  4.\  inches  in  length 
to  7  or  8,  the  centre  being  therefore  usually  behind  the  condyle.^ 

Elevation. — The  simplest  form  which  this  movement  may  take  is 
that  which  is  the  reverse  of  the  one  just  described,  the  jaw  pursuing  the 
movement  of  depression  in  reverse  order.  The  temporal,  masseter,  and 
internal  pterygoid  contract,  serving  to  rotate  the  jaw  about  a  horizontal 
'axis  passing  through  the  condyles.     The  shape  of  the  glenoid  fossae 

Fig.  1S4 


Diagram  illustrating  the  path  pursued  by  the  mandible  in  depression.  G.  F,  glenoid  fcssa; 
R,  centre  of  condyle;  R  F,  path  pursued  by  centre  of  condyle;  A,  cutting  edge  of  lower  central 
incisors;  A  B,  path  which  would  be  described  by  A  if  the  mandible  rotated  about  R  and 
condyle  remained  in  fossa;  A-  C,  actual  path  pursued  by  A  in  depression  of  the  mandible; 
A,  approximate  centre  of  rotation  for  path  A  C  actually  pursued  by  the  point  A. 


being  such  as  to  guide  the  condyles  backward,  they  recede,  the  posterior 
elastic  fibres  of  the  capsule  likewise  carrying  the  cartilage  back.  In 
moving  from  the  position  of  extreme  depression,  the  contraction  of  the 
levators  produces  rotation  about  the  condyles,  the  temporal  muscle  being 
most  advantageously  situated  for  this  action.  The  stylo-maxillary 
ligaments,  from  their  point  of  attachment,  serve  in  the  beginning  to  cause 
a  distal  movement  of  the  condyles  as  rotation  takes  place.  As  elevation 
proceeds,  this  is  contributed  to  by  the  external  lateral  ligaments  and  by 
the  posterior  fibres  of  the  capsular  ligament,  while  the  upward  inclina- 
tion of  the  fossae  serves  to  guide  the  condyles  upward  and  backward. 
For  the  jaw  to  pursue  this  path  there  must  be  full  and  complete  relaxation 
of  the  external  pterygoids,  or  the  condyles  w^ill  not  move  backward. 
After  a  certain  point  has  been  reached,  these  muscles  have  the  power 


^  Tomes  and  Dolamore, 
^  Loc.  cit. 


Transactions  Odontological  Society  of  Great  Britan,  1900,  p.  167. 


208  THE  HUMAN  DENTAL  MECHANISM. 

of  fixing  the  condyles  on  their  return  path  to  the  distal  part  of  the 
glenoid  fosste,  and  then  elevation  consists  in  a  rotation  of  the  jaw 
about  them  in  this  position.  If  they  do  not  relax,  or  if  there  is  con- 
traction of  the  protrusor  fibres  of  some  of  the  levator  muscles,  the 
elevation  may  have  combined  with  it  some  of  the  movement  of  protru- 
sion. Tomes  and  Dolamore^  found  that  in  normal  closure  of  the  jaw 
the  path  of  its  anterior  end  is  almostconstantly  anterior  to  that  of  open- 
ing. It  is  possible  for  the  mandible  to  move  from  its  most  depressed 
position  to  that  of  occlusion,  to  that  of  extreme  protrusion,  or  to  any 
position  between  these,  by  paths,  which  depend  in  their  character  upon 
the  proportion  of  protrusive  movement  combined  with  the  elevation. 

Protrusion — When  the  natural  teeth  are  in  occlusion  the  jaw  can- 
not be  carried  forward  until  it  has  been  slightly  depressed  to  disengage 
the  cusps.  In  an  edentulous  mouth  however  this  does  not  obtain. 
The  jaw  is  moved  forward  by  the  action  of  the  external  pterygoids 
contracting  simultaneously,  assisted  by  the  external  fibres  of  the 
masseter  and  the  anterior  fibres  of  the  temporal  and  some  fibres  of  the 
internal  pterygoid  (Constant).  The  external  pterygoid  also  pulls  for- 
ward the  interarticular  cartilage,  this  movement  however  being  also 
due  to  the  intimacy  of  its  attachment  to  the  condyle  by  means  of  the 
capsular  ligament.  The  condyles  move  downward  and  forward,  thus 
depressing  the  distal  portion  of  the  lower  jaw  on  the  average  about 
I  of  an  inch,  a  fact  brought  out  by  BalkwilP  and  later  by  Walker^  and 
several  investigators  since  him,  the  amount  of  the  depression  being 
determined  by  the  inclination  of  the  glenoid  fossa  and  differing  vastly 
in  different  individuals.  In  the  most  forward  position  assumed  by 
the  jaw  in  protrusion,  the  condyle  is  nearly  upon  the  eminentia  arti- 
cularis.  This,  however,  is  not  as  far  forward  as  in  the  position  of 
greatest  depression,  for  in  addition  to  the  joint  ligaments  proper,  the 
stylo-maxillary,  and  other  tissues  attached  to  the  back  of  the  ramus 
are  put  on  the  stretch  and  prevent  the  forward  movement  of  the 
condyle,  unless  it  is  rotated  forward  as  occurs  in  depression  of  the 
mandible. 

Retraction. — This  is  the  reverse  of  the  movement  of  protrusion,  and 
the  jaw  may  be  brought  back  along  the  same  path  which  it  pursued 
in  the  forward  movement.  This  is  produced  by  the  contraction  of 
the  posterior  fibres  of  the  temporal,  the  internal  portion  of  the  masse- 
ter, the  digastric,  the  genio-hyoid  and  mylo-hyoid  muscles.  The  condyle 
is  carried  backward  and  upward,  the  cartilage  accompanying  it.  There 
may  be  combined  with  this  various  amounts  of  depression,  as  for  in- 
stance, the  jaw  may  move  from  its  most  protruded  position  back  to 
that  of  occlusion,  or  to  its  most  depressed  position,  or  to  any  point  or 
along  any  path  intervening  between  the  two.  In  moving  from  the  most 
protruded  to  the  most  depressed  position,  the  stylo-maxillary  and  the 
posterior  fibres  of  the  capsular  ligament  being  on  the  stretch,  cause  the 
condyle  to  be  moved  forward  and  downward. 

^  Loc.  eit. 

'   Transactions  of  Odontological  Society  of  Great  Britain    Vol.  v.,  p.  133. 

'  The  Dental  Cosmos.  Vol.  xxxviii.,  p,  34. 


LATERAL  MOVEMENTS. 


209 


Combinations  of  these  two  kinds  of  movements  may  occur  in  various 
amounts.  Thus  far  we  have  considered  the  movements  which  the 
lower  jaw  may  make  by  simultaneous  and  equalized  contraction  of 
the  muscles  of  both  sides. 

Lateral  Movements. — The  lateral  excursions  of  the  mandible  are 
made  possible  by  the  sliding  character  of  the  temporo-mandibular 
joint  and  the  fact  that  protrusion  may  occur  independently  on  either 
side.  The  external  pterygoid  muscle  does  not  operate  in  a  plane 
identical  with  or  parallel  to  that  in  which  the  condyle  moves  in  its  forward 

Fig,  185 


Diagram  illustrating'  action  of  external  pterygoid  muscle.  R,  stationary  centre  of  rotation  in 
right  condyle  ;  P.line  of  action  of  left  pterygoid  ;  A  B,  path  pursued  by  point  A  on  contrac- 
tion of  left  external  pterygoid. 


excursion.  Its  action  is  to  pull  the  condyle  inward  as  well  as  forward  and 
it  is  only  by  the  simultaneous  contraction  of  both  that  the  jaw  is  bodily 
protruded.  (Fig.  185.)  Acting  singly,  therefore,  when  the  condyle  on 
the  opposite  side  is  held  in  the  fossa,  its  influence  is  to  draw  the  condyle 
inward,  forward  and  downward  over  the  inclined  floor  of  the  fossa, 
causing  a  rotation  of  the  mandible  about  a  vertical  axis  passing  through 
the  opposite  condyle.  In  this  movement  the  path  of  the  condyle  (Fig. 
186),  is  approximately  in  the  arc  of  a  circle  upon  the  floor  of  the  fossa, 
and  it  may  be  carried  no  farther  forward,  if  indeed,  as  far  as  in  the  move- 
ment of  protrusion.  The  simplest  form  of  the  return  movement  is  for 
the  condyle  to  pursue  the  same  path  back  to  its  distal  position  in  the 
fossa.  When  the  jaw  is  carried  to  the  other  side  in  its  lateral  excursion, 
the  opposite  condyle  in  turn  is  pulled  downward  and  forward,  and  the 
jaw  rotates  about  the  other. 


14 


210 


THE  HUMAN  DEXTAL  MECIIAXISM. 


This  movement  may  be  combined  with  that  of  depression  of  the  jaw 
as  above  described.  In  this  event  the  Uiteral  movement  simply  seems 
to  make  an  alteration  in  the  position  of  the  horizontal  axis  al)out  which 
the  rotation  element  of  the  movement  of  depression  takes  place.  The 
greater  the  forward  pull  on  one  condyle  as  related  to  the  other,  and 
hence  the  greater  the  lateral  movement,  the  less  depression  may  })e 
combined  with  it,  and  as  the  depression  increases  the  lateral  movement 
must  of  necessity  decrease.  We  have  seen  that  in  the  most  depressed 
position  of  the  lower  jaw  both  condyles  are  in  the  most  forward  and 
downward  position  near  the  eminentite  articulares,  from  which  position 


Fig.    186 


Diagram  iUustrating  forward  and  lateral  excursions  of  the  mandible.  R.  O,  path  pur- 
sued by  right  condyle  when  jaw  is  rotated  to  the  left  about  L;  LP,  path  pursued  by 
left  condyle  when  jaw  is  rotated  to  the  right  about  R;  R  F'  and  L  F,  paths  pursued  by 
right  and  left  condyles  respectively  when  mandible  is  carried  bodily  forward. 


it  is  impossible  to  produce  any  lateral  movement.  Lateral  movement 
and  depression  in  any  combination  of  these  two  are  always,  therefore, 
inversely  related  to  each  other. 

Lateral  movement  may  also  be  combined  with  forward  translation 
of  the  jaw,  its  rotation  about  a  vertical  axis  then  occurring  at  the  place 
in  which  the  condyle  through  which  it  passes  is  fixed  in  the  glenoid 
fossa.  This  means  simply  that  the  condyle,  about  which  rotation  in 
the  lateral  movement  has  occurred,  is  not  in  its  distal  position  in  the 
fossa,  but  has  been  carried  forward  along  with  its  fellow  of  the  opposite 
side.  It  becomes  evident  that  these  movements  are  similarly  inversely 
related,  for  the  farther  forward  one  condyle  is  carried,  the  less  distance 
remains  to  the  other  for  rotation  about  it.  It  may  be  said  that  the  condyle 
in  the  most  distal  position— the  one  about  which  rotation  takes  place — 


THE  TEETH.  211 

always  occupies  a  point  in  the  path  pursued  in  tlieir  dual  forward  move- 
ment. The  return  movements  partake  of  the  character  of  their  con- 
stituents as  may  be  seen  above. 

The  various  combinations  of  depression  with  forward  translation, 
and  the  addition  to  these  of  changes  in  the  direction  of  the  horizontal 
axis  of  rotation  passing  through  the  condyles,  which  their  independent 
movement  forward  produces,  gives  to  the  mandible  a  range  of  movement 
beyond  that  of  any  other  joint  in  the  body.  Within  the  limitation  im- 
posed by  the  joint  ligaments,  and  when  the  teeth  are  not  in  contact,  the 
position  of  the  jaw  at  any  one  time  is  determined  by  the  balance  estab- 
lished between  the  opposed  pairs  of  muscles  which  produce  its  move- 
ments. When  the  teeth  touch,  however,  they  beome  a  factor  in  deter- 
mining the  position  of  the  forward  end  of  the  mandible.  It  is  evident, 
therefore,  that  so  long  as  they  are  in  contact,  their  form  and  position  has 
much  to  do  with  the  position  of  the  jaw  and  its  paths  of  movement. 
The  slight  laxity  of  the  ligaments,  and  the  compressibility  of  the  tissues 
intervening  between  the  bones  and  the  varying  pull  of  the  muscles  allow 
some  slight  latitude  in  the  paths  pursued. 

The  Teeth. — The  jaws  are  equipped  with  the  teeth  in  two  opposed 
series  which  serve  as  specialized  organs  in  the  mechanical  subdivision 
of  the  food.  As  the  armament  for  the  fixed  and  moveable  elements  of 
masticating  apparatus  they  are  brought  into  functional  relation  by  the 
muscles  operating  the  mandible.  In  the  typical  or  ideal  denture 
they  are  of  such  form  and  arrangement  as  to  best  subserve  the  inter- 
ests of  the  masticatory  function. 

In  order  to  comprehend  the  various  relations  which  the  teeth  have 
during  the  functional  activity  of  the  mechanism,  and  to  see  how  its  ends 
are  best  subserved  by  their  form  and  arrangement,  it  will  first  be  neces- 
sary to  study  the  teeth  of  each  jaw  separately,  particularly  with  regard 
to  their  occlusal  surfaces.  Then,  as  the  position  of  occlusion  is  the 
ultimate  one  toward  which  the  mandible  tends  in  all  its  masticatory 
efforts,  it  will  be  necessary  to  study  the  relative  position  of  these  morsal 
surfaces  when  the  teeth  are  in  occlusion,  and  then  their  relation  during 
the  masticatory  movements  of  the  mandible  may  be  understood.  In- 
asmuch as  we  are  considering  them  as  mechanical  appliances  solely, 
no  attempt  will  be  made  to  give  their  anatomy  except  as  it  concerns 
this  matter. 

As  viewed  from  their  occlusal  surfaces,  the  teeth  (Figs.  187  and  188), 
are  seen  to  be  arranged  in  the  jaws  in  two  arch-shaped  series  of  sixteen 
teeth  each.  The  outline  of  the  arch  in  general  is  that  of  a  parabola. 
While  it  varies  considerably  within  the  limits  of  the  normal,  as  will  be 
seen  under  the  head  of  Temperament,  its  form  is  related  to  several  other 
variable  factors  to  be  considered  conjointly  later  in  this  chapter,  and 
variations  in  this  particular  may  occur  which  are  not  at  the  expense  of 
the  mechanical  effectiveness  of  the  apparatus.  The  arch  outhne  is 
largely  determined  by  the  position  of  the  indi\adual  teeth,  but  is  affected 
by  their  size — both  actual  and  relative — and  their  shape.  The  general  pro- 
portion existing  between  the  size  and  form  of  the  individual  teeth  in  either 


212 


THE  HUM  AX  DENTAL  MECHANISM. 


the  upper  or  the  lower  series  is  fairly  constant.  Slight  variations  occuij 
but  as  they  are  more  important  from  a  cosmetic  than  from  a  functional 
standpoint,  they  will  not  be  considered  here.  The  proportion  between 
the  corresponding  teeth  of  the  upper  and  lower  series  of  any  denture  is 
also  practically  constant,  the  individual  teeth  in  one  jaw  being  nearly 
always  associated  with  those  of  corresponding  size  and  shape  in  the  other. 
This  will  be  seen  more  clearlv  when  their  occlusion  is  discussed. 


FiQ.  187 


Occlusal  surfaces  oi  the  ui>ner  teeth. 


Fig. 

188 

It  Tm 

1 

1 

1 

I 

1 

^' 

J 

^^Hki'^'      1 

■ 

■ 

■  "^  '^ 

M 

! 

! 

i 

1 

Occlusal  surfaces  of  the  lower  teeth. 


The  outlines  of  the  upper  and  lower  arches  correspond  in  shape  in 
order  that  the  teeth  may  be  opposed  throughout  their  series,  except  that 
the  upper  is  slightly  larger  and  Qverhangs  the  lower  externally.  This 
difference  in  size  is  necessary  in  order  that  the  fixed  base  shall  present  a 
sufficientlv  large  surface  for  contact  durino;  the  excursions  of  the  move- 
able  arm  and  it  is  extended  in  the  direction  of  these  movements.  This 
is  due  to  the  greater  size  of  the  upper  teeth  and  the  greater  segmental 
form  of  the  arch :  both  the  overhanging  and  difference  in  size  decrease 
from  the  median  line  backward. 


THE  OCCLUSION  OF  THE  TEETH.  213 

The  teeth  of  each  arch  (Figs.  1S7  and  188)  are  seen  to  present  an 
unbroken  series  of  occlusal  surfaces  extending  from  the  terminal  molar 
on  one  side  to  that  on  the  other.  Besides  giving  greater  surface  area 
for  masticatory  purposes,  this  approximal  contact  provides  a  mutual 
support  for  the  teeth  which  is  of  great  value.  When  the  character  of 
man's  food  is  remembered,  it  will  be  seen  that  this  provision  is  also 
of  some  importance  for  the  protection  against  injury  of  the  soft  tissues 
of  the  interproximal  space. 

The  teeth  are  divided  into  four  classes  anatomically,  and  their  func- 
tions as  mechanical  instruments  more  or  less  correspond  to  this  division. 
As  viewed  from  their  occlusal  surfaces,  (Figs.  187  and  188),  it  will  be 
noted  they  are  well-shaped  for  their  several  offices.  The  incisors  are 
designed  to  cut  off  definitely  sized  masses  of  food,  and  their  morsal  sur- 
face is  in  the  form  of  a  broad  blade,  the  labial  and  lingual  surfaces 
meeting  at  an  angle  at  the  incisal  edge.  The  canines  in  the  lower 
animals  serve  largely  for  prehension — to  pierce  and  hold  the  more 
resistent  food,  and  among  the  carnivora  to  guide  the  lower  jaw 
into  place.  In  man  these  functions  are  largely  rudimentary,  the 
tooth  being  intermediate  in  function  between  the  incisors  and 
bicuspids.  It  has  a  double  blade  ending  in  a  well  defined  point. 
The  bicuspids,  as  their  name  implies,  have  two  cusps,  and  are 
intermediate  between  the  canines  and  molars.  While  their  func- 
tion is  largely  to  crush  and  press  the  food,  they  participate  in 
trituration,  which  is  the  characteristic  office  of  the  molars.  The  greater 
sharpness  of  their  cusps  fits  them  more  for  piercing  than  for  grinding. 
The  molars  are  the  grinding  teeth  proper,  for  which  their  tuberculated 
surfaces  are  well  designed.  The  cusps  alternate  with  fossae  and 
grooves,  and  are  joined  by  ridges  which  afford  a  surface  most  effective 
for  trituration  as  will  be  seen  later. 

It  will  be  observed  of  the  molar  and  bicuspid  series  of  cusps  and 
depressions  of  each  jaw,  that  as  they  are  higher  and  larger  anteriorly, 
they  are  smaller  and  shorter  as  the  distal  end  is  approached,  so  also 
there  is  a  diminution  in  the  distance  between  them  both  mesio-distally 
and  bucco-lingually. 

The  Occlusion  of  the  Teeth. — When  the  ideal  or  typical  denture  is 
viewed  in  occlusion,  (Fig.  189),  it  will  be  seen  that  there  is  a  definite 
mutual  relation  of  the  occlusal  surfaces  of  the  teeth.  It  will  be  observed 
that  there  are  two  different  types  of  occlusion — first,  that  correspond- 
ing to  the  incisors  and  canines,  in  which  the  morsal  edges  do  not  meet 
end  to  end,  but  those  of  the  lower  teeth  rest  upon  the  lingual  surfaces  of 
the  upper;  and  second,  that  corresponding  to  the  molar  and  bicuspid 
teeth,  where  considered  collectively  their  cusps  are  either  received  into 
fossae  or  depressions  in  the  occlusal  surface  of  the  opposing  series, 
or  overlap  the  buccal  or  lingual  surface  of  their  opponents.  It  is 
notable  that  with  the  exception  of  the  lower  central  incisors  and  the 
upper  third  molars,  each  tooth  is  opposed  by  portions  of  two  others. 
This  provision  serves  to  dissipate  the  force  of  impact  in  occlusion, 
and  tends  to  preserve  the  integrity  of  the   denture;    for   with  this 


214 


THE  HUMAN  DENTAL  MECHANISM. 


arrangement  the  loss  of  a  tooth  in   one  arch  does  not  mean  the  loss 
of  a  tooth  in  the  other  througli  lack  of  antagonism. 


Fir,,    is'l 


Upper  and  lower  teeth  in  occlusion.     (From  jihotograph  of  specimen  in  the  Wistar  Institute 

of  Anatomy.) 

The  Occlusion  of  the  Incisors — The  typical  occlusion  for  the  incisors 
is  shown  in  Fig.  190,  in  which  it  will  be  seen  that  the  upper  incisors 
overhang  the  lower  for  about  one  third  their  labial  surfaces.      This 

Fig.  190 


fV 

'  I^^^^^^^^^^^^^M 

i 

<           ^ 

Occlusion  of  the  incisor  teeth.     (Fnjm  photograph  of  specimen  No.  4237,  Wistar  Institute 

of  Anatomy.) 


relation  is  spoken  of  as  the  normal  overbite  of  the  incisor  teeth  and  ob- 
tains in  a  large  percentage  of  cases.  The  angle  formed  by  the  long 
axes  of  the  upper  and  lower  incisors  differs  much  in  individuals,  as  will 
be  seen  under  Temperament,  and  the  contact  between  the  two  varies 


THE  OCCLUSION  OF  THE  BICUSPIDS  AND  MOLARS. 


215 


in  consequence.  In  some  the  angle  is  so  obtuse  that  tliere  is  con- 
siderable contact  between  the  labial  surface  of  the  lower  and  the 
lingual  surface  of  the  upper  incisors.  The  size  of  the  arcli  of  the  upper 
may  be  so  great  that  the  lower  teeth  are  not  in  contact  with  the  up])er  in 
the  position  of  occlusion,  only  coming  in  contact  when  the  lower  jaw  is 
protruded  in  incision.  The  so  called  "edge-to-edge"  bite  of  the 
incisors,  which  is  seen  in  those  temperaments  in  which  the  over- 
bite has  been  short  and  the  teeth  have  worn,  or  have  been 
originally  erupted  in  this  position  (Fig.  191,  B),  is  within  the  range  of 
the  normal  but  is  a  less  effective  mechanical  arrangement  for  incision. 


Fio.  19; 


A  B 

Occlusion  of  the  incisor  teeth.     A.  Normal  overbite;     B.  Edge-to-i 
incisors  distal  to  lower.     (Grevers.) 


bite;     C.  Upper 


The  condition  presented  by  Fig.  191,  C,  in  which  the  upper  in- 
incisors  occlude  lingually  to  the  lower  is  less  effective  still,  because 
the  lower  jaw  cannot  move  backward  to  bring  the  teeth  into  contact. 

In  a  typical  denture  BalkwilF  has  pointed  out  with  regard  to  the 
scissors-like  action  of  the  front  teeth,  that  as  they  are  wedge  shaped, 
he  "expected  to  find  the  angle  of  the  wedge  equally  divided  by  the 
circleof  motion,  which  would  give  the  greatest  dividing  power,"  but  this 
is  not  the  case.  The  angle  of  the  wedge  points  more  outward  in  the 
upper  and  inward  in  the  lower,  and  he  reminds  us  that  in  closing  the 
teeth,  there  is  a  backward  as  well  as  an  upward  motion.  Burchard 
has  pointed  out  the  effect  of  this  motion  upon  the  direction  of  the  im- 
pact of  the  teeth  during  closure  of  the  jaw;  that  unless  there  were  a  back- 
ward movement  at  the  same  time  the  effect  would  be  to  drive  the  upper 
incisors  forward.  Constant^  has  shown  that  the  direction  of  impact 
in  ordinary  closing  is  almost  vertical. 

The  Occlusion  of  the  Bicuspids  and  Molars. — The  bicuspids  and  mo- 
lars on  each  side  viewed  collectively  (Fig.  194),  may  be  considered  as 
consisting  of  a  series  of  cones  or  cusps  alternating  with  fossae  or  de- 
pressions, and  so  fitted  together  when  the  teeth  are  in  occlusion  that  the 
fossae  receive  cusps  of  the  opposing  teeth.  The  inner  line  of  cusps  of 
the  upper  are  received  into  the  fossae  between  the  outer  and  inner  cusps 


1  Transactions  Odontological  Society  of  Great  Britain,  Vol.  v.,  p.  133. 

2  Naked  Eye  Anatomy  of  the  Human  Teeth,  p.  187. 


21() 


THE  HUMAN  DEXTAL  M  ECU  AX  ISM. 
Fio.   102 


Occlusion  of  the  molar  and  bicuspid  teeth,  external  view.     (From  photograph  of  specimen  in  posses- 
sion of  Dr.  F.  A.  Peeso.) 

Fi.;.  I'j:-; 


Occlusion  of  the  molar  and  bicuspid  teeth,  internal  view.     (From  photograph  of  specimen  in  posses- 
sion of  Dr.  F.  A.  Peeso.     Same  specimen  as  Fig.  192.) 


THE   OCCLUSION  OF  THE  BICUSPIDS  AND   MOLARS. 


217 


of  the  lower  (Fig.  193),  the  outer  line  of  cusps  of  the  lower  being  corres- 
pondingly received  into  fossae  in  the  upper  (Fig.  192).  Thus  the  lin- 
gual cusp  of  the  first  upper  bicuspid  (Fig.  193)  is  received,  between  the 
buccal  and  lingual  cusps  of  the  lower  bicuspids,  the  point  of  the  cusp 
corresponding  to  the  line  between  the  mesial  marginal  ridge  of  the  sec- 
ond and  distal  marginal  ridge  of  the  first.  Similarly,  the  lingual  cusp 
of  the  second  upper  bicuspid  is  received  at  the  line  of  contact  between 
the  marginal  ridges  of  the  second  lower  bicuspid  and  first  molar.  The 
mesio-lingualcuspof  the  first  upper  molar  fits  into  the  central  fossa  of  the 
first  lower  molar, while  the  disto-lingual  cusp  occupies  a  position  in  relation 


Fig.   194 


Occlusion  of  the  molar  and  bicuspid  teeth,  occlusal  view.  Lines  are  drawn  from  the  lingual 
cusps  of  the  upper  teeth  and  buccal  cusps  of  the  lower  to  the  corresponding  depressions  into 
which  they  fit.  (From  photograph  of  specimen  in  possession  of  Dr.  F.  A.  Peeso.  Same  as  Figs. 
192  and  193.) 


with  the  adjoining  marginal  ridges  of  the  first  and  second  lower  molar 
teeth,  i.e., in  the  depression  between  the  disto-lingual  and  buccal  of  the 
first  lower  molar  and  mesio-lingual  and  mesio-buccal  of  the  second 
lower  molar.  The  second  upper  molar  occludes  similarly  with  the  lower 
second  and  third  molars,  while  the  third  upper  molar  varies  in  this  re- 
spect as  it  varies  in  form.  The  large  lingual  cusp,  usually  found  on 
this  tooth,  however,  normally  occupies  the  central  fossa  in  the  third 
lower  molar. 

The  buccal  cusps  of  the  lower  are  received  into  the  fossae  and  depres- 
sions of  the  upper  teeth  as  follows  (Fig.  192) :  The  buccal  cusp  of  the 
first  lower  bicuspid  is  in  relation  with  the  distal  marginal  ridge  of  the 
canine  and  the  mesial  marginal  ridge  of  the  first  bicuspid  (Fig.  194). 
This  is  less  like  a  cup-shaped  depression  than  any  which  succeed  in  this 
description.  The  second  bicuspid  has  its  bucca;l  cusp  received  in  the 
depression  between  the  buccal  and  lingual  cusps  of  both  upper  bicuspids, 


218  THE  HUM  AX  DENTAL  MECHANISM. 

its  point  being  in  definite  relation  with  their  udjaeent  marginyl  ridges. 
The  mesio-buccal  cusp  of  the  first  lower  molar  rests  in  relation  with 
tlie  adjoining  marginal  ridges  of  the  first  upper  molar  and  the  second 
bicuspid,  while  the  large  buccal  cusp  is  received  in  the  central  fossa  of 
the  first  upper  molar.  The  disto-buccal  cusp  of  the  first  lower  molar, 
which  is  present  in  50  per  cent,  of  cases,  is  usually  so  distaliy  located 
that  it  shares  with  the  mesio-buccal  cusp  of  the  second  lower  molar  the 
space  between  the  cusps  of  the  first  and  second  upper  molars  and  is  in 
contact  with  their  adjacent  marginal  ridges;  or  it  is  forced  to  the  lingual 
to  be  lost  in  the  distal  marginal  ridge.  The  mesio-buccal  cusp  of  the 
second  lower  molar  has  just  l)een  located,  while  the  remainder  of  the 
tooth  is  similarly  related  to  the  upper  first  and  second  molars  as  the 
first  molar  is  to  its  two  antagonists.  The  third  lower  molar  varies  so 
in  form  that  it  is  difficult  to  say  what  is  its  typical  occlusion.  The 
two  types  most  commonly  seen  (Broomell)*  are  those  with  four  or  five 
cusps  respectively,  the  occlusion  being  similar  to  the  molars  already 
described  with  regard  to  the  mesio-buccal  and  buccal  cusps  in  either 
case,  while  where  the  fifth  cusp  is  present,  it  occludes  simply  with  the 
distal  portion  of  the  upper  molar. 

The  buccal  cusps  of  the  upper  molars    and  bicuspids  are  sharper 
than  the  corresponding  lingual  cusps  (Fig.    195).     They  are  related  to 

Fig.  195 


Section  through  upper  and  lower  teeth  in  occlusion,  showing  relative  height  and  sharpness  of 
buccal  and  lingual  cusps.     (Cryer.) 

the  lower  teeth  as  follows:  (Fig.  192.)  That  of  the  first  bicuspid  is  re- 
ceived in  the  groove  between  the  buccal  cusps  of  the  lower  bicuspids  and 
to  the  buccal  side  of  the  teeth.  That  of  the  second  corresponds  to  the 
space  between  the  buccal  cusp  of  the  second  lower  bicuspid  and  me.sio- 
buccal  of  the  first  lower  molar.  The  mesio-buccal  of  the  first  upper 
molar  is  received  in  the  buccal  groove  of  the  first  lower  molar,  the  disto- 
buccal  cusp  occupying  the  disto-buccal  groove,  where  the  lower  molar 

"^  Broomell:  Anatomy  and  Histology  of  the  Mouth  and  Teeth. 


THE  OCCLUSION  OF  THE  BICUSPIDS  AND  MOLARS.  21!) 

has  five  cusps,  or  the  space  between  the  second  molar  and  the  first,  where 
it  has  four.  The  buccal  cusps  of  the  second  upper  molar  occlude  so  sim- 
ilarly to  those  of  the  first  that  they  recjuire  no  mention,  while  the  two 
buccal  cusps  of  the  third  likewise  similarly  occlude,  except  where  the 
lower  molar  has  no  disto-buccal  cusp  when  only  its  last  cusp  is  in  re- 
lation with  the  distal  surface  of  the  lower  tooth. 

As  to  the  lingual  cusps  of  the  lower  teeth  (Fig.  193),  they  are  in  general 
smaller  and  more  pointed  (Fig.  195) ,  than  the  buccal.  A  marked  excep- 
tion exists  in  the  case  of  the  first  lower  bicuspid  whose  lingual  cusp  is 
frequently  so  rudimentary  as  to  be  represented  only  by  a  ridge  of  enamel; 
the  second  is  sometimes  similarly  formed.  BonwilP  has  pointed 
out  the  lack  of  function  of  this  cusp  of  the  first  bicuspid,  which  fact 
will  be  seen  more  clearly  when  the  functions  of  the  teeth  are  described. 
When  present  this  cusp  is  in  relation  only  with  the  mesial  slant  of  the 
lingual  cusp  of  the  first  upper  bicuspid.  The  lingual  cusp  of  the  second 
is  lingually  placed  to  the  space  between  the  lingual  cusps  of  the  two 
upper  bicuspids,  while  the  mesio-lingual  cusp  of  the  first  lower  molar  is 
similarly  placed  between  the  first  molar  and  second  bicuspid.  The 
disto-lingual  cusp  corresponds  in  position  with  the  lingual  groove  of  the 
first  upper  molar.  The  lingual  cusps  of  the  second  molar  are  similarly 
related  to  the  first  and  second  upper  molars,  and  this  is  likewise  fre- 
quently true  for  the  third  lower  molar,  with  the  exception  of  its  disto- 
lingual  cusp,  which,  having  no  groove  with  which  to  be  in  relation, 
touches  only  the  distal  incline  of  the  single  lingual  cusp  of  the  upper 
wisdom  tooth. 

It  will  be  noted  that  the  cusps  received  into  fossae  are  the  more 
rounded,  that  the  cusps  which  overlap  are  the  sharper  and  the  smaller. 
(Fig.  195.) 

In  the  upper  jaw  it  is  noted  that  the  fossse  are  separated  antero-pos- 
teriorly  or  mesio-distally  by  the  transverse  ridges  of  the  bicuspids  and 
by  the  mesial  marginal  and  oblique  ridges  of  the  molars.  These  ridges 
are  received  by  the  grooves  separating  the  buccal  cusps  of  the  lower  teeth. 
The  lower  fossse  and  depressions  which  receive  the  lingual  cusps  of  the 
upper  series  are  similarly  separated,  and  these  ridges  are  received  into 
the  grooves  separating  the  lingual  cusps  of  the  upper  teeth  (Fig.  194.) 
It  is  evident  that  in  order  to  move  the  jaw  in  any  direction  it  must  be 
depressed  to  disengage  the  cusps  from  these  fossae. 

The  actual  height  of  the  cusps  and  the  corresponding  depth  of  the 
fossse  vary  greatly  in  different  individuals  and  will  be  discussd  later 
under  the  head  of  Temperament.  It  may  be  mentioned  here  however 
that  this  variable  factor  is  one  of  that  related  group  which  will  be  con- 
sidered later  in  this  chapter.  Bonwill  ^  has  stated  that  there  is  an 
almost  constant  relation  between  the  overbite  of  the  incisors  and  the 
length  of  the  cusps  of  the  bicuspid  and  molar  teeth.  (Fig.  196.)  Wliere 
the  overbite  is  considerable,  the  molars  and  bicuspids  will  usually  be 
found  to  possess  high  cusps,  the  overhanging  of  the  buccal  cusps  of 
the  upper  being  an  index  of  their  length,  while  short  cusps  are  associated 

^  American  System  of  Dentistry,  Vol.  ii.,   p.  495.  _    '  Ibid.,  p.  488. 


220 


THE  HUMAN  DENTAL  MECHANISM. 


with  a  small  amount    of   overbite.      In    either  event  the  cusps  grow 
proportionally  shorter  from  before  l)ack\vard.     AMiilc  this  proportion 


Fia  196 


Diagram  showing  fj-pical  proportion  between  cusp  length  and  overbite.     Modified  from  BonwUI. 

is  fairly  constant  for  typical  dentures,   many  instances  of  a  departure 
from  it  are  found.    A  denture  conforming  closely  to  the  description  of  the 
typical  denture  in  every  particular  except  this,  is  shown  in  Fig.  197. 
The  canine  tooth  occupies  a  position  between  the  incisors  and  the 


Fig.   197 


Denture  typical  in  other  respects  exhibiting  disproportion  between  cusp  length  and  overbite 
It  will  be  noted  that  the  cusps  of  the  first  molar  are  much  worn  as  this  is  oldest  tooth  in  mouth 
(From  photograph  of  specimen  from  Dr.  Cryer's  collection.) 

masticating  teeth  and  hence  is  intermediate  in  the  character  of  its  oc- 
clusion.    "VSTiere  from  the  shape  of  the  arch  it  continues  the  line  of  the 


THE  OCCLUSION  OF  THE  BICUSPIDS  AND  MOLARS.  221 

molars  and  bicuspids,  it  partakes  more  of  their  type  of  occlusion,  and 
its  overbite  corresponds  to  the  overlapping  of  the  molar  and  bicuspid 
cusps  and  is  proportioned  to  them  in  this  regard.  When  its  position  is 
more  in  the  line  of  the  incisors,  it  partakes  of  their  type  of  occlusion,  its 
overbite  corresponding  with  theirs,  while  if  it  is  intermediate  in  posi- 
tion, it  participates  in  the  character  of  both  types  of  occlusion. 

This  relation  of  cusp  length  and  overbite  is  another  of  the  related 
variations  to  be  discussed  presently.  When  the  overbite  and  cusp 
length  are  not  thus  proportioned  the  condition  may  be  referred  to  as 
abnormal. 

We  next  come  to  discuss  some  peculiarities  of  the  occlusion  of  the 
bicuspid  and  molar  teeth,  which  are  so  closely  related  to  the  manner  of 
movement  of  the  mandible  and  have  so  important  a  bearing  upon  the 
efficiency  of  these  teeth  as  masticatory  organs,  that  it  will  be  necessary 
to  bear  in  mind  the  movements  of  which  the  lower  jaw  is  capable  in 
order  to  understand  the  functional  significance  of  these  characteristics. 
If  a  curved  line  be  drawn  touching  the  summits  of  the  buccal  cusps  of 
the  upper  teeth  from  canine  to  third  molar,  it  will  more  or  less  accurately 
correspond  to  the  arc  of  a  circle  with  its  convexity  downward.     (Fig. 


Fig.  198 


Diagram  illustrating  the  "compensating  curve,"  or  the  "Curve  of  Spee." 

198.)  The  upper  lingual  cusps  will  be  found  to  occupy  a  similar  line  and 
both  series  of  cusps  of  the  lower  teeth  correspond  also  to  the  arc  of  a 
circle.  This  condition  is  to  be  attributed  to  differences  in  the  level 
of  the  teeth  and  in  the  direction  of  their  long  axes  as  they  are  placed  in 
the  alveolar  process.  The  long  axes  of  the  upper  teeth  anterior  to 
the  second  bicuspid  are  inclined  toward  the  median  line  of  the  denture, 
that  of  the  second  bicuspid  being  practically  vertical,  while  the  teeth 
distal  to  it  are  placed  at  a  higher  level  in  the  bone  and  have  their 
long  axes  increasingly  inclined  away  from  the  median  line.  In  the 
lower  jaw  a  corresponding  condition  is  found,  successive  cusps  of  the 
series  being  placed  at  higher  levels  in  each  direction  from  the  mesial  cusps 


ooo  Tf"-^  II  I'M  AX  DEXTAL  MECHANISM. 

of  tlic  first  molar  wliiflimarks  the  lowest  portion  of  the  curve.  (Fig.  19.S.) 
This  is  frequently  spoken  of  as  the  "eonipensatinireurve"  of  the  molars 
and  bicuspids,  aiid  also  as  the  "Curve  of  vSpce,"  by  whom  it  is 
described.^  This  curve  varies  considerably  in  difl'erent  individuals. 
In  its  most  ideal  form,  if  continued  in  a  projection  of  the  jaw  upon  the 
vertical  sagittal  plane,  it  touches  the  anterior  face  of  the  articular  surface 
of  the  condyle.  (Fig.  199.)  It  more  frequently  passes  posterior  to  this 
than  anterior.  In  typical  dentures  its  form  has  a  definite  relation  to  two 
of  their  characteristics  which  have  already  been  mentioned,  viz.,  the 
length  of  the  cusps  of  the  teeth,  and  the  path  which  the  condyles  pursue 
in  the  forward  excursion  of  the  jaw.  The  relation  existing  between  the 
curve  and  these  two  factors  may  be  stated  thus:  the  longer  the  cusps  of 
the  molars  and  bicuspids  the  shorter  will  be  the  radius  of  this  curve, 
and  the  shorter  the  cusps  the  longer  will  be  its  radius;  also,  the  greater 

Fig.  199 


The  "Curve  of  Snee."  Line  passing  through  anterior  face  of  condyle.     (From  a  photograph  of 
a  specimen  in  the  Wistar  Institute  of  Anatomy.) 

the  inclination  of  the  glenoid  fossic  and  hence  the  greater  the  angle  be- 
tween the  path  of  the  condyles  and  the  horizontal,  the  less  will  be  the 
radius  of  this  curve,  while  the  more  nearly  horizontal  is  the  path  of  the 
condyles  in  their  forward  movement,  the  longer  will  be  the  radius  of 
the  compensating  curve.  To  understand  the  bearing  of  this  feature 
of  the  occlusal  surfaces  of  the  bicuspid  and  molar  teeth  upon  the 
forward  excursion  of  the  jaw,  let  us  see  what  takes  place  if  this  move- 
ment occurs  and  the  lower  teeth  maintain  contact  with  the  upper,  simply 
sliding  forward  over  their  occlusal  surfaces.  It  must  be  evident  that 
the  path  of  the  jaw  would  be  determined  during  this  movement  by  the 
condyles  and  fo.ss.ne  po.steriorly  and  by  the  teeth  anteriorly.  The  object 
which  this  arrangement  serves  is  that  all  of  the  bicuspid  and  molar 
teeth  shall  be  in  contact  within  a  certain  range  of  the  forward  and  back- 
ward movement  of  the  mandible.  It  likewise  provides  that  when  the 
mandible  is  elevated  into  contact  with  the  upper  jaw  not  too  far  for- 

1    "Die  Verschiebungsbahn  des  Unterkiefers  am  Schiidel."      F.  Graf  v.  Spee;    Arch.  f.  Anat 
u.  Physiol,  1890. 


THE  OCCLUSION  OF  THE  BICUSPIDS  AND  MOLARS.  223 

ward  of  the  position  of  occlusion,  the  lower  teeth  may  simultaiie(ni.sly 
strike  their  opponents  and  be  able  to  preserve  a  sliding  contact  with 
them  in  the  retraction  of  the  jaw  to  the  position  of  occlusion. 

We  have  already  seen  that  the  position  of  the  lower  jaw  at  any  time 
when  the  teeth  are  in  contact  is  determined  anteriorly  by  this  contact  of 
the  teeth,  and  posteriorly  by  the  glenoid  fossa  upon  which  the  condyle 
rests.  Its  path,  therefore,  during  a  sliding  contact  of  the  teeth,  would  be 
determined  anteriorly  by  the  teeth  and  posteriorly  by  the  fossse  over 
which  the  condyles  move.  That  there  must  be  a  correspondence  be- 
tween these  is  evident.  In  order  to  understand  how  it  is  possible  for 
this  sliding  contact  of  the  teeth  to  take  place,  and  for  sake  of  simplicity 
in  description,  let  us  suppose  that  the  opposed  surfaces  are  smooth  in- 
stead of  being  broken  up  into  cusps  and  fossas.  (Fig.  199.) 

In  order  that  the  lower  teeth  may  slide  upon  the  upper  and  the  con- 
tact be  interrupted  at  no  point,  the  sliding  surfaces  must  be  either  per- 
fectly flat  or  represent  a  curved  plane,  a  section  of  which  would  be  the  arc 
of  a  circle.  These  are  the  only  two  kinds  of  surfaces  between  which  a 
sliding  contact  could  take  place.  In  the  former  case  the  sliding  body 
moves  in  a  straight  line,  in  the  latter  in  the  arc  of  a  circle.  That 
the  condyle  must  move  in  a  path  harmonious  with  that  pursued  by  the 
teeth  of  the  lower  jaw  becomes  evident  when  it  is  remembered  that  the 
jaw  moves  as  a  whole.  Where  the  sliding  surfaces  are  planes  and  the 
jaw  moves  in  a  straight  line,  the  condyle  moves  in  a  line  parallel  to  this 
or  identical  with  it.  When  they  correspond  to  the  arc  of  a  circle,  the 
condyle  moves  also  in  the  arc  of  a  circle,  its  path  concentric  with  or 
identical  with  it.  If  this  did  not  occur  the  sliding  contact  between  the 
teeth  would  be  interrupted. 

We  find  therefore  that  when  the  general  line  of  the  teeth  is  that  of 
the  arc  of  a  circle,  that  portion  of  the  fossa  over  which  the  condyle  slides 
is  likewise  an  arc  which  is  either  identical  or  concentric.  And  the 
more  nearly  the  plane  of  the  teeth  approaches  a  straight  line  or  an 
arc  with  an  infinite  radius,  the  more  nearly  straight  is  the  floor  of  the 
fossa.  These  two  associated  and  related  characteristics  vary  therefore 
in  individuals.  With  a  well  defined  curve  of  the  molars  and  bicuspids 
there  must  be  a  corresponding  slant  of  the  glenoid  fossae  to  permit  the 
condyles  to  descend  as  the  jaw  sweeps  round  this  curve,  while  where 
they  are  more  nearly  in  a  straight  line  and  the  jaw  may  move  the  more 
bodily  forward,  the  fossae  do  not  incline  downward  so  much  but  permit 
the  condyles  to  go  more  horizontally  forward. 

The  addition  of  cusps  to  the  surface  of  the  teeth  complicates  very 
much  this  sliding  contact.  In  fact  the  surfaces  do  not  slide  as  such,  but 
the  points  of  the  cusps  of  the  lower  teeth  glide  upon  the  fossae  of  the 
upper.  We  have  already  seen  that  from  before  backward  the  cusps  get 
proportionately  shorter  and,  of  course,  the  fossae  into  which  they  are 
received  are  proportionately  shallower.  As  the  mandible  is  moved  for- 
ward these  cusps  have  the  effect  of  separating  the  jaws,  or  of  rotating  the 
mandible  about  a  horizontal  axis  passing  through  the  condyles.  This 
is  produced  by  the  lower  buccal  cusps  sliding  upon  the  anterior  walls  of 


224 


THE  HUMAN  DENTAL  MECHANISM. 


their  fos.sjie,  while  the  fossae  in  the  lower  teeth  containing  the  lingual 
cusps  of  the  upper  teeth  slide  upon  them.  This  provision  keeps  the 
cusps  in  contact  during  the  forward  movement,  until  the  incisors  come 
into  action,  and  where  the  normal  overbite  exists,  the  lower  centrals  then 
slide  down  the  lingual  surface  of  the  upper  incisors  and  separate  the 
distal  teeth.  Usually  when  the  incisors  are  edge-to-edge,  all  the  teeth 
distal  to  them  are  out  of  contact. 

From  what  has  been  said  it  wall  be  seen  that  the  buccal  cusps  of  the 
lower  teeth  and  the  lingual  cusps  of  the  upper  are  the  ones  which  it  is  most 
important  should  conform  to  the  compensating  curve,  since  they  are 
in  contact  with  the  fossae.  One  of  the  commonest  variations  from 
this  typical  arrangement  which  will  be  observed,  is  that  in  which  the  distal 
cusps  of  the  upper  molars  are  below  the  curve  mentioned,  the  long  axes 

Fig.  200 


Fig. 

201 

BPK^^^ 

1 

BBr^ 

f>  ^^^^H 

QP 

^^^^^^^^ 

■ 

^J 

The  "Curve  of  Spee."  Short  cusps  and 
long  curve.  Line  passing  through  anterior 
face  of  condyle.  (Specimen  No.  4237,  Wis- 
tar  Institute  of  Anatomy.) 


The  "Curve  of  Spee."  Short  cusps  and 
long  curve.  Line  passing  distal  to  anterior 
face  of  condyle.  (From  photograph  of 
specimen  No.  800,  Wistar  Institute  of 
Anatomy.) 


of  the  teeth  being  almost  vertical  (Fig.  189).  In  such  cases  if  the  jaws 
are  t\'pical  in  other  respects  the  mesio-buccal  cusps  will  be  found  more 
or  less  worn  down  to  conform  to  the  general  plan,  the  disto-buccal  re- 
maining unworn,  because  they  occupy  space  between  the  lower  teeth 
and  not  in  their  buccal  grooves. 

Another  characteristic  of  the  molar  and  bicuspid  teeth  may  be  observed 
in  Figs.  202  and  203,  in  which  it  may  be  seen  that  their  buccal  and  lin- 
gual cusps  are  not  on  the  same  level,  the  buccal  cusps  occup\ing  a 
higher  relative  position  as  we  proceed  backward  from  the  first  bicus- 
pid. In  the  upper  jaw  the  lingual  cusp  of  the  first  bicuspid  is  usually 
higher  than  the  buccal,  the  cusps  of  the  second  bicuspid  being  either  on 
the  same  level  or  the  buccal  being  a  little  higher  (Fig.  202).  The  buccal 
cusps  of  the  first  molar  are  successively  higher  than  the  lingual,  and  this 
continues  until  we  find  those  of  the  third  molar  relatively  highest  of 
all  (Fig.  202).  This  condition  obtains  also  in  the  lower  jaw  (Fig. 
203).  It  is  pardy  due  to  an  actual  anatomical  difference  in  the  height 
of  the  cusps  as  the  tooth  is  viewed  out  of  the  mouth,  and  partly 
due  to  the  increasing  inclination  of  the  long  axes  of  the  teeth  in  the 


THE  OCCLUSION  OF  THE  BICUSPIDS  AND  MOLARS.         225 


alveolar  process.     This  is  another  of  the  related  factors  subsequently 

Fiii.  202 


Upper  and  lower  bicuspid  and  molar  teeth,  side  \-iew,  showing  relative  height  of  buccal 
and  lingua]  cusps  of  upper  teeth.  (From  photograph  of  a  specimen  in  the  Wistar  Institute  of 
Anatomy.) 

Fig.  203 


Lower  bicuspid  and  molar  teeth,  front  -v-iew,  showing  relative  height  of  buccal  and  hngual 
cusps.  Same  mandible  as  Fig.  202.  (From  photograph  of  a  specimen  in  the  Wistar  Institute  of 
Anatomy.) 

to  be  considered  and  varies  with  the  path  of  the  condyle.     That  this 
condition  provides  for  the  contact  of  the  cusps  in  the  lateral  excursion 

15 


226 


THE  HUMAN  DENTAL  MECHANISM. 


of  the  jaw  has  been  well  brought  out  l)y  Walker'  (Fig.  20')).  When 
the  jaw  is  moved  to  one  side  with  the  teeth  sliding  in  contaet  it  rotates 
about  a  vertical  axis  passing  through  the  condyle  on  that  side,  the 
opposite  condyle  moving  inward,  forward,  and  downward.  On  the 
side  toward  which  the  movement  is  taking  place,  the  rounded  buccal 
and  the  lingual  cusps  of  the  lower  teeth  slide  upon  and  come  in  contact 
with   the   buccal  and  lingual  cusps,  respectively,  of  the   upper  teeth. 


Fig.   204 


Diagrammatic  view  of  the  relative  height  of  the  buccal  and  lingual  cusps  of  the  molar  and 
bicuspid  teeth.     (W^alker.) 

On  the  opposite  side  the  high  buccal  of  the  lower  teeth  slide  up  and 
come  in  contact  with  the  high  lingual  of  the  upper  teeth,  which  is 
rendered  possible  by  the  fact  that  the  jaw^  is  depressed  on  that  side.  If 
the  condyle  simply  moved  forward  instead  of  downward  as  well,  the 
buccal  and  lingual  cusps  might  be  of  the  same  height  and  this  same  re- 
lation of  the  cusps  would  obtain,  but  as  it  moves  downward  the  outer 
cusps  have  to  be  higher  in  order  that  there  shall  be  compensation  for 

Fig.  205 


Diagram  illustrating  contact  of  cusps  in  lateral  excursion  of  the  mandible.  Section 
through  jaws  at  position  of  second  molar.  OP,  line  touching  lingual  cusps  of  upper  molars; 
L  R,  line  touching  buccal  cusps  of  upper  molars;  S  T  line  touching  buccal  cusps  of  lower 
molr>.'-=.  showing  the  downward  movement  of  the  mandible  on  the  right  side  necessary  for  contact 
of  the  cusps. 

the  rotation  of  the  jaw   about  a  horizontal  axis  passing  through  the 
stationary  condyle. 

This  provision  serves  to  balance  the  masticating  force  and  prevent 
overstrain  when  the  jaws  are  in  occlusion  in  the  lateral  position.  It 
provides  contact  of  the  teeth  on  both  sides  to  resist  the  strain  exerted 
by  the  pairs  of  levators  which  have  simultaneously  contracted.     Witb 

^  The  Dental  Cosmos.  Vol.  xxxix.,  p.  789. 


THE  OCCLUSION  OF  THE  BICUSPIDS  AND  MOLARS.  227 

artificial  dentures  this  condition  may  be  imitated  to  advantage  for  a 
purpose  to  be  discussed  in  a  later  chapter.  Thus  it  will  be  seen  that  in 
the  movement  of  the  jaw  forward  or  from  side  to  side  there  are  a  series 
of  cones  which  may  be  applied  to  the  food,  the  series  of  cones  or  depres- 
sions so  alternating  and  being  so  arranged  in  each  jaw  that  within  a 
certain  range  of  movement  the  whole  series  of  cones  may  be  in  contact 
with  opposing  surfaces  of  some  sort.  The  immense  functional  value 
of  this  is  obvious,  and  it  is  also  apparent  that  this  provision  tends 
toward  preventing  overstrain  and  undue  shock  upon  the  denture. 

In  exerting  the  force  by  which  the  food  is  crushed,  the  jaw  moves  to 
what  has  been  called  the  position  of  occlusion,  from  the  various  positions 
which  it  has  assumed  in  biting  through  the  food  placed  between  the 
teeth.  There  are  several  ways  in  which  the  food  may  be  crushed  in 
such  movements.  It  may  be  done  by  the  action  of  a  cone-shaped  point 
not  closely  fitting  its  opposing  surface,  which  is  applied  to  the  food  and 
acts  as  a  dividing  wedge;  or  the  cone  may  be  received  into  a  depression 
which  it  closely  fits,  the  food  being  simply  crushed  as  between  two  plane 
surfaces,  or  the  cone  may  not  fit  the  depression,  there  being  space  or 
spaces  for  the  crushed  food  to  escape,  the  cone  in  the  depression  acting 
somewhat  as  a  pestle  in  a  mortar.  Two  closely  fitting  plane  or 
curved  surfaces,  when  the  force  between  them  is  exerted  at  a  right 
angle  to  the  surf  aces,  do  not  act  well  for  crushing  except  for  rather  brittle 
substances.  But  if  in  addition  to  their  approximation  they  slide  upon 
each  other,  the  crushing  effect  is  increased. 

A  cusp  received  into  an  accurately  fitting  depression  does  not  possess 
the  greatest  efficiency  for  crushing.  Clearance  spaces  must  be  provided. 
During  the  operation  of  the  denture  as  the  food  is  pressed  toward  the 
buccal  and  lingual  surfaces  of  the  teeth,  grooves  between  the  cusps 
and  the  interdental  spaces  are  provided  for  clearance.  Grooves  run 
down  to  the  bottom  of  the  depressions  in  the  bicuspid  and  molar 
teeth,  and  the  chief  clearance  channels  are  located  between  the 
buccal  cusps  of  the  upper  and  the  lingual  cusps  of  the  lower. 
This  carries  the  food  lingually  above  the  tongue  so  that  it  may  be 
manipulated  more  easily,  while  bucally  is  carried  downward  into 
the  sulcus  between  cheek  and  teeth,  where,  because  of  the  peculiar  mus- 
culature of  the  cheek  and  because  the  lower  jaw  is  depressed  below  this 
point  when  the  mouth  is  opened,  the  food  is  again  carried  in  between 
the  teeth.  This  overhanging  of  cusps  also  serves  to  protect  the 
cheek  on  the  outside  and  the  tongue  on  the  inside  from  being  caught 
between  the  surfaces  of  the  teeth. 

In  addition  to  the  fact  that  the  forms  of  the  occlusal  surfaces  of  the 
teeth  peculiarly  fit  them  to  act  as  the  crushing  organs  of  the  mechanism 
we  find  that  they  are  adapted  for  this  function  in  other  particulars. 
They  are  provided  with  the  means  of  resisting  the  wear  and  stress  which 
the  constant  activity  of  the  apparatus  entails. 

The  enamel  of  the  teeth,  the  hardest  tissue  of  the  body,  forms  their 
external  covering.  It  gives  them  a  hard,  resistant,  and  highly  polished 
surface,  and  offers  its  greatest  thickness  to  those  parts  most  exposed  to 


228 


THE  HUMAN  DENTAL  MECHANISM. 


wear.  The  enamel  masses  are  also  arranged  to  give  the  best  mechani- 
cal support  in  resistance  of  the  force  exerted  upon  the  teeth.  The  hulk 
of  the  tooth  is  composed  of  dentine  which  confers  the  necessary  strength. 
Resistance  to  the  stress  of  mastication  is  provided  for  by  the  form  and 
location  of  the  roots  of  the  teeth.  These  are  all  modified  cones  fitting 
into  conical  sockets, and  as  their  long  axes  are  generally  in  line  with  the 
direction  in  which  stress  is  exerted  upon  them,  the  mechanical  advan- 
tage is  evident.  The  force  upon  the  incisors  does  not  always  act  to  force 
them  into  their  sockets  (Figs.  206,  207,  and  200).  For  the  upper  it 
serves  to  drive  them  forward  as  well  as  upward,  and  is  resisted  by  the 


Fig.  206 


Fig.  207 


Fig.  208 


Line  of  resistance  to  force 
offered  by  upper  central  in- 
cisor.    (Burchard.) 


tine  or  resistance  to  force 
offered  by  upper  lateral  in- 
cisor.       (Burchard.) 


Lines  of  resistance  to  force 
offered  by  upper  canine, 
(Burchard.) 


Fig.  209 


Lines  of  resistance  to  force  upon  the  lower  incisors  and  canine  teeth.     (Hurcliard.) 


flattened  labial  surfaceof theirroots.  The  canineis  forced  u])ward  and 
outward  and  the  labial  surface  of  its  root  also  serves  to  prevent  displace- 
ment in  this  direction  (Fig.  208).  The  six  lower  anterior  teeth  are 
forced  downward  and  inward,  the  inclination  of  their  roots  and  their 
arch-like  arrangement  resisting  the  strain  upt)n  them.  The  principal 
strain  upon  molars  and  bicuspids  is  vertical,  their  roots  l)eing  well  dis- 
posed to  resist  it  (Figs.  210  and  211).  The  lateral  stress  upon  these  teeth, 
which  is  largely  determined  by  the  height  of  their  cusps,  is  resisted  by 
the  direction  of  their  roots.  As  the  princi})al  lateral  strain  upon  the 
upper  molar  and  bicuspid  teeth  i.s'  inward,  we  have  their  long  axes  in- 
clined in  the  direction  to  resist  this  (Fig.  210). 

The  opposite  is  true  of  the  lower  molars  whose  long  axes  resist  a 


TIIK  OCCLUSION  OF  THE  BICUSPIDS  AM)  MOLARS.  229 

force  tending  to  displace  them  downward  and  outward — the  direction 
in  which  strain  in  mastication  is  apphed  to  them.   (Fig.  211.) 

The  character  of  the  retentive  tissues  of  the  teeth  tends  to  prevent 
and  resist  strain  upon  them.  The  pericementum  is  composed  largely 
of  connective  tissue  fibres  extending  from  the  tooth  to  its  socket,  and  so 
disposed  as  to  support  the  tooth  even  under  great  pressure  on  its  long 
axis,  but  by  their  elasticity  permitting  slight  movement  in  any  direction. 
The  membrane  is  also  highly  vascular,  particularly  in  youth,  which 
doubtless  also  contributes  to  its  resiliency.  This  mol)ility  enables  the 
tooth  to  resist  far  greater  force  exerted  upon  it  than  if  it  were  solidly 
attached  to  the  bone,  and  the  independent  mobility  of  theteeth  makes 
the  denture  capable  of  resisting  greater  strain  than  if  they  were  a  united 
mass.  The  teeth  mutually  support  each  other  because  of  their  approxi- 
mal  contact,  so  that  each  tooth  is  thus  able  to  resist  greater  force.      The 

Fig.   210  Fiq.  211 


Lines  of   force  upon  an  upper  molar.  Lines  of    force  upon  a  lower  molar. 

(Burchard.)  (Burchard.) 

pericementum  has  upon  the  tooth,  a  vital  protective  influence  as  well 
as  a  cushioning  effect.  Black^  has  reminded  us  that  its  tactile  sensi- 
bility is  a  constant  safeguard  against  overstrain. 

It  has  been  stated  that  there  are  a  number  of  characteristics  of  the 
typical  denture  which  are  variable,  and  that  they  are  all  more  or  less 
directly  related,  and  that  they  vary  harmioniously  and  proportionately. 

Those  which  have  been  mentioned  are: 

1.  The  size  and  shape  of  the  individual  teeth. 

2.  The  overbite  of  the  incisors  and  the  cusp  length  of  the  molars 
and  bicuspids. 

3.  The  shape  of  the  dental  arch. 

4.  The  curve  of  Spee  or  "  the  compensating  curve." 

5.  The  inclination  of  the  long  axes  of  the  teeth. 

6.  The  relation  of  the  buccal  and  lingual  cusps  of  the  bicuspid  and 
molar  teeth. 

7.  The  shape  of  the  condyle  and  the  inclination  of  the  glenoid  fossa. 
In  what  may  be  called  typical  dentures  variations  in  any  of  the  above 

may  and  do  occur  without  the  creation  of  a  departure  from  the  mechanical 

•   The  Dental  Cosmos.  Vol.  xxxviii.,  p.  476. 


230  THE  HUMAX  DENTAL  MECHANISM. 

design,  provided  they  are  assoeiated  with  variations  in  other  eharacter- 
istics  to  which  thty  are  directly  rehited.  The  mutual  relation  of  these 
has  been  pointed  out  as  they  were  described.  The  only  item  mentioned 
which  is  not  a  characteristic  of  the  denture  is  the  last,  which  of  course 
determines  the  path  and  the  manner  of  movement  of  the  jaw.  The 
relationship  existing  between  this  and  the  anatomical  form  of  the 
teeth  is  the  most  important  one  to  bear  in  mind.  It  has  been  well 
stated  by  Walker^  that  "there  is  a  certain  definite  co-relation  between 
the  morphology  of  the  morsal  surfaces  of  the  teeth"  and  the  path  pur- 
sued by  the  condyle. 

The  foregoing  description  has  been  that  of  the  ideal  or  typical  mas- 
ticatory apparatus  rather  than  the  normal  or  usual.  Few  dentures 
absolutely  perfect  in  every  particular  exist,  it  is  indeed  doubtful  if  any 
do.  A  number  which  are  approximately  perfect  have  been  used  to 
illustrate  this  chapter.  Nature  has  been  prolific  in  her  provision  for  man's 
needs  in  this  regard,  and  while  she  has  furnished  few  with  a  perfect 
mechanism,  yet  within  the  bounds  of  what  may  be  termed  the  normal, 
many  dentures  exist,  which  although  they  fall  short  of  the  mechanical 
design  described  in  many  particulars,  nevertheless  serve  their  posses- 
sors for  purposes  of  mastication  in  an  entirely  satisfactory  manner. 
The  human  organism  frequently  displays  its  ability  to  adapt  itself 
to  serious  shortcomings  in  the  work  of  this  apparatus,  but  it  must 
not  be  forgotten  that  the  greater  the  departure  from  this  typical  design 
the  less  must  be  the  efficiency  of  the  mechanism. 

THE  PREPARATION  OF  FOOD. 

Incision. — Having  studied  the  characteristics  of  the  masticating 
mechanism,  we  are  prepared  to  discuss  the  method  by  which  it  func- 
tionates. Prehension,  or  the  seizing  of  the  food,  is  a  function  of  the 
teeth  of  some  of  the  lower  animals  but  is  unnecessary  with  civilized 
man.  His  first  act  is  that  of  incision,although  with  the  development  of 
cutting  instruments  for  food  and  the  cultivation  of  a  conventional  use  of 
them,  even  incision  is  confined  to  few  articles.  In  the  performance  of 
this  act  the  lower  jaw  is  depressed  from  the  position  of  occlusion  and 
carried  forward,  the  condyles  moving  approximately  evenly  in  their 
fossae  in  this  direction,  rotation  of  the  jaw  about  them  occurring  suffi- 
ciently to  permit  a  grasping  of  the  substance  to  be  incised.  The  food 
is  carried  through  the  lips  in  contact  with  the  upper  incisorteeth,  when 
the  jaw  is  elevated  and  partly  retruded,  the  edges  of  the  lower  and 
upper  incisor  teeth  being  approximately  opposite  during  the  movement. 
The  more  resistent  the  food,  the  more  nearly  will  the  teeth  be  opposed 
in  their  course  through  it.  As  soon  as  their  cutting  edges  come  in  con- 
tact, the  retraction  of  the  jaw  is  so  combined  with  elevation  that  the 
edges  of  the  lower  incisors  slide  up  the  lingual  surfaces  of  the  upper, 
the  incisal  edges  passing  each  other  somewhat  after  the  order  of  shears. 
In  some   cases  where  the  normal  overbite  of   the    incisors  described 

^  The  Dental  Cosmos.  Vol.,  xxxviii.,   p.  576. 


MASTICATION.  231 

on  page  214,  does  not  exist,  the  curve  of  the  occkisal  surfaces  of  the 
molars  is  such  that  the  third  molar  in  its  advanced  position  due  to 
the  protrusion  of  the  jaw,  is  in  contact  with  the  second  molar  dur- 
ing incision,  thus  tending  to  relieve  the  strain  upon  the  incisor  teeth. 
This  is  usual  where  there  is  an  edge-to-edge  bite,  but  with  a  normal 
overbite  it  does  not  occur. 

It  will  be  noted  (Fig.  190),  from  the  curve  of  the  occlusal  edges  of 
the  upper  incisors,  the  laterals  usually  being  lower  than  the  centrals, 
that  their  edges  are  first  opposed  in  the  centre,  and  thus  the  shearing 
action  is  carried  on  in  both  directions  from  this  point.  It  is  also  noted 
that  when  the  edges  come  into  contact  the  food  has  been  practically 
severed,  and  that  until  this  time,  the  direction  of  the  stress  upon  the 
upper  teeth  is  almost  that  of  the  long  axes  of  the  teeth,  while  for  the 
lower  incisors  this  is  not  true  until  the  cutting  edges  begin  to  slide 
upon  the  upper  incisors,  the  stress  up  to  this  time  being  such  as  to 
displace  them  downward  and  forward. 

Mastication. — Man's  diet  consists  of  food  of  various  degrees  of 
physical  consistence,  and  while  the  tendency  of  civilization  is  toward 
such  preparation  of  the  food  as  to  lessen  the  necessity  of  mastication, 
some  of  it,  indeed,  requiring  none  at  all,  yet  the  bulk  of  it  demands  a 
thorough  trituration  to  best  subserve  the  body's  needs.  The  principal 
articles  of  human  diet  requiring  mastication  are  meats  (animal  fibre), 
vegetable  fibre,  and  cereals,  and  foods  made  from  them.  Some  of 
the  other  vegetable  products  have  a  hard  protective  covering  which 
must  be  broken  through  to  give  access  to  the  digestive  juices,  for  it 
has  been  demonstrated  that  some  of  them,  as  grain  for  instance,  might 
pass  unaltered  through  the  alimentary  canal  if  this  were  not  done. 
From  a  mechanical  standpoint  the  essential  feature  of  mastication 
is  to  crush  these  various  articles  of  food  in  order  to  break  up  their 
physical  organization  and  reduce  the  size  of  their  separate  particles. 
The  object  of  this  operation  is  to  facilitate  the  action  of  the  digestive 
fluids  upon  the  food  and  render  its  passage  through  the  alimen- 
tary canal  easily  accomplished. 

After  the  food  has  been  incised  or  after  an  appropriately  sized 
portion  has  been  introduced  into  the  cavity  of  the  mouth,  it  is  passed 
back  by  the  tongue  to  the  bicuspid  and  molar  teeth  to  be  reduced  to 
small  particles.  In  accomplishing  this  the  jaw  executes  two  more 
or  less  distinct  kinds  of  movements  and  there  are  various  combinations 
of  them.  The  first  of  these  is  the  direct  up  and  down  motion  of  the 
jaw  in  which  it  moves  in  the  sagittal  plane ;  the  morsal  surf  aces  are  sepa- 
rated and  the  food  placed  between  them  is  crushed  when  they  are 
approximated.  The  great  crushing  ability  of  tuberculated  surfaces  is  a 
well-known  mechanical  principle,  the  cones  acting  as  wedges  to  divide 
the  food.  The  efficiency  of  the  denture  in  this  movement  is  propor- 
tional to  the  height  of  the  cusps,  sufiicient  clearance  spaces  being  nec- 
essary, as  has  heretofore  been  shown.  This  motion  is  pecuhar  to  the 
carnivorous  animals,  their  masticating  efforts  being  practically  limited 
to  it.    Black  has  stated  that  this  kind  of  masticating  motion  is  used 


232  THE  HUMAN  DENTAL  MECHANISM. 

almost  exclusively  in  the  mastication  of  meats  by  persons  with  fairly 
normal  dentures.  The  ultimate  position  attained  by  the  jaw  in  this 
motion  is,  of  course,  as  nearly  that  of  occlusion  as  the  crushed  fibre  in- 
terposed between  the  surfaces  will  allow.  The  jaw  does  not  always 
close  so  that  the  cusps  are  exactly  opposite  their  respective  fossae: 
hence  a  small  sliding  takes  place  to  bring  the  teeth  togetlier,  but  in 
the  main  the  movement  is  toward  the  position  of  occlusion,  the  food  being 
squeezed  in  a  pulpy  mass  buccally  and  lingually. 

The  other  motion,  which  in  its  simplest  form  is  similar  to  that  charac- 
teristic of  herbivorous  animals,  is  produced  during  the  lateral  excursion 
of  the  jaw.  The  mandible  is  depressed  and  carried  to  one  side,  the  con- 
dyle on  the  side  toward  which  it  is  moving  usually  remaining  in  the 
distal  portion  of  the  fossa,  that  of  the  opposite  side  l)eing  pulled  forward. 
The  jaw  is  then  elevated  in  this  lateral  position,  the  food  being  inter- 
posed, and  the  rounded  buccal  cusps  of  the  lower  teeth  on  this  side 
come  into  relation  with  the  sharp  buccal  cusps  of  the  upper,  the  inner 
cusps  likewise  touching;  the  food  is  crushed  and  cut,  a  portion  of  it 
being  left  to  occupy  the  foss{e  between  the  inner  and  outer  cusps. 
The  jaw  is  then  pulled  upward  and  inward  toward  its  occlusal  posi- 
tion, the  food  being  crushed  between  the  rounded  and  strong  lower 
buccal  cusps  and  upper  lingual  cusps.  With  this  movement  is  fre- 
quently combined  a  slight  protrusion,  though  this  is  largely  a  matter  of 
habit,  and  is  not  by  any  means  necessary  for  the  most  efficient  action 
of  the  teeth.  While  this  is  occurring  on  one  side,  on  the  other  the 
teeth  are  not  brought  into  the  same  functional  relations.  The  high 
cusps  above  and  below  are  usually  in  contact  at  one  or  more  points, 
which  serves  to  prevent  strain  and  offers  resistance  to  the  elevator 
muscles  of  this  side  which  contract  simultaneously  wath  those  on  the 
opposite  side.  This  side  does  not  functionate  during  the  excursion 
of  the  jaw  to  the  other  side,,  because  only  the  upper  lingual  and  lower 
buccal  cusps  are  in  contact.  This  motion  is  used  in  the  crushing  of 
cereals  and  food  made  from  them,  and  is  by  far  the  more  effective  of 
the  two.  It  is  also  used  in  crushing  most  of  the  brittle  and  very  hard 
substances.  In  the  normal  denture  mastication  of  this  nature  takes 
place  instinctively  upon  the  two  sides  alternately,  although  this  is 
largely  a  question  of  habit. 

The  force  required  in  crushing  various  articles  of  human  diet,  by  an 
up  and  down  motion,  has  been  investigated  by  Blacks  He  used  an 
instrument,  consisting  of  two  molar  teeth  carved  from  brass,  which  are 
forced  against  corresponding  teeth  by  the  direct  thrust  of  a  sliding  bar. 
Head^  has  reduced  the  figures  thus  obtained  by  Black  by  the  use  of  a 
device  for  producing  a  triturating  as  well  as  a  crushing  movement. 
He  utilized  "  a  natural  skull  with  practically  perfect  molars  of  average 
size."  This  was  inverted,  arranged  with  weights  suspended  from 
the  lower  jaw,  and  "so  tipped  that  the  force  of  gravity  would,  during 

*   The  Dental  Cosmos,  Vol.  xxxviii.,  p.  484. 

2  The  Human  Skull  used  as  a  Gnatho-dynamometer  to  Determine  the  Value  of  Trituration 
in  the  Mastication  of  Food.     Paper  read  before  Union  meeting,  Washington,  1900. 


MASTICATION.  233 

mastication,  give  a  sliding  or  triturating  motion."  The  comparative 
table,  appencUnl  below,  gives  the  results  in  pounds  obtained  bv  these 
two  investiirators. 

Dr.  Head's  Dr.  Black'8 

Raw  cabbage 16  lbs.  40 — 00  lbs. 

Raw  onion 4     " 

Head  lettuce 8    "  25 — 30    " 

Radish,  whole  broke 20 — 25  lbs  20 — 25    " 

Pieces  radish,  pulverized 10 — -25    "  3.5 — 40    " 

Corned  beef 18 — 22"  30 — 35     " 

Boiled  beef 3           " 

Tongue    1 —  2  "                          3 —  5   •' 

Lamb  chop 16 — 20  " 

Roast  lamb 4            " 

Roast  lamb  kidney 3            " 

Tenderloin  of  beefsteak  (very  tender) 8 —  9"  35 — 40    " 

Sirloin  steak 10 — 20—43   " 

Round  of  beefsteak,  tough 38—42  "  60 — 80   " 

Roast  beef    20 — 35"  35 — .50    " 

Boiled  ham 10 — 14"  40 — 60    " 

Broiled  ham 10 — 13   " 

Pork  chops 25—30"  20—25    " 

Roast  veal _ 16            "  35 — 40    " 

Veal  chops 12 

Roast  mutton 18 — 22  '' 

Mastication  is  a  voluntary  act,  but  the  co5rdinating  mechanism  once 
having  been  set  in  motion  by  the  v>'ill,  it  continues  reflexly  and  auto- 
matically, and  is  independent  of  conscious  action.  The  food,  having 
been  passed  into  the  mouth,  is  carried  back  to  the  molar  and  bicuspid 
teeth  and  crushed  after  the  manner  already  described.  The  tongue 
is  the  principal  agent  in  keeping  it  between  the  crushing  surfaces. 
The  tonic  contraction  of  the  orbicularis  oris  in  the  lips  and  the  buccin- 
ator in  the  cheeks  opposes  the  tongue,  active  action  of  either  occurring 
w'hen  necessary,  while  within  the  arch  the  tongue  shifts  the  food  from 
side  to  side  between  the  morsal  surfaces  as  may  be  necessary,  the  rugae 
affording  a  rough  surface  upon  which  it  may  be  rolled.  The  saliva, 
which  is  constantly  secreted  in  the  mouth  and  which  flows  in  greater 
abundance  under  the  stimulation  of  the  presence  of  food  and  of  masti- 
cation, is  mixed  with  the  food.  It  softens  the  food,  dissolving  some  of 
its  soluble  constituents,  adds  a  digestive  ferment,  and  its  mucin  assists 
in  agglomerating  and  lubricating  the  mass  for  deglutition.  It  also 
lubricates  the  soft  tissues  which  play  about  the  teeth.  During  the 
process  of  mastication  the  teeth  not  only  crush  the  food,  but  also  func- 
tionate as  organs  of  exquisite  tactile  sensibility,  giving  instant  knowledge 
of  the  location  of  the  alimentary  particle  and  of  its  physical  consistence. 

Deglutition. — After  the  food  has  been  masticated  and  mixed  with 
saliva,  it  is  gathered  into  a  bolus  upon  the  tongue,  the  edges  of  w^iich 
are  curved  upward  to  form  a  gutter.  The  anterior  portion,  being 
lifted  by  its  intrinsic  muscles  and  the  stylo-glossus,  is  in  contact  with 
the  anterior  portion  of  the  palatal  vault,  the  rugae  affording  here  also 
a  roughened  surface  against  which  it  is  placed.  The  soft  palate  is 
then  lifted  by  the  levatores  palati  to  touch  the  posterior  wall  of  the 
pharynx,  which  has  been  bulged  forward  to  meet  it  by  the  action  of  its 


234  THE  HUMAN  DENTAL  MECHANISM. 

superior  constrictor.  At  the  same  time  the  funnel-shaped  pharynx  is 
brought  up  by  the  palato-pharyngeus  and  the  stylo-pharyngeus  to 
cover  the  mass,  which  is  then  shot  past  the  pillars  of  the  fauces  by  the 
pressure  exerted  upon  the  tongue  by  the  contraction  of  the  mylo-hyoid 
and  of  the  hyoglossi  (Kronecha  and  Metzger);  the  opening  into  the 
larynx  is  closed  by  the  contraction  of  the  lateral  crico-arytenoids  and  the 
constrictors  of  the  glottis,  by  the  elevation  of  the  larynx,  and  partly  by 
the  epiglottis,  although  the  part  taken  by  the  latter  structure  is  of  small 
importance.  The  peristaltic  action  of  the  oesophagus  then  carries  the 
food  to  the  stomach. 


THE  LOSS  OF  THE  TEETH. 

It  is  beyond  the  purpose  of  this  work  to  discuss  the  causes  which  re- 
sult in  the  loss  of  the  teeth.  SuflBce  it  to  say  on  this  subject  that  the 
absence  of  the  teetli  is  so  frequent  an  accompaniment  of  old  age  as  to 
be  looked  upon  as  one  of  its  usual  features.  An  edentulous  condition 
is  not  the  result  of  natural  physiological  processes  analogous  to  those  by 
which  the  accomodation  fails  from  a  weakening  of  the  ciliary  muscle 
and  a  hardening  of  the  crystalline  lens,  or  the  hair  turns  gray  in  old  age 
from  a  disappearance  of  its  pigment.  The  teeth  are  lost  from  patho- 
logical processes  which  either  receive  no  treatment  or  are  unsuccess- 
fully treated;  from  accidental  causes;  or  are  removed  surgically  in 
the  treatment  of  diseased  conditions.  Unfortunately  it  frequently 
happens  that  they  are  lost  from  these  causes  before  the  period  of  old 
age. 

Effect  upon  Mastication. — The  effect  of  the  loss  of  the  teeth  upon 
the  masticatory  function  may  be  readily  understood  since  their  part  in 
it  has  been  described.  As  each  tooth  performs  a  definite  portion  of  the 
work  of  the  mechanism,  its  loss  is  followed  by  a  definite  interference 
with  that  work.  The  loss  of  one  tooth  deprives  the  opposed  series  of 
one  of  its  antagonists,  and  renders  it  functionally  useless  at  this  point. 
The  loss  of  a  tooth  also  deprives  the  adjacent  teeth  of  the  support  of 
approximal  contact.  WTiile  some  teeth  are  more  important  than  others 
and  their  loss  is  followed  by  more  serious  consequences,  yet  in  gen- 
eral, the  loss  of  teeth  having  antagonists  increases  proportionately  the 
deficiencies  of  the  apparatus. 

The  function  peculiar  to  any  class  of  teeth  is  affected  by  their  loss. 
Whenthe  incisors  are  missing,  the  incisive  function  suffers;  when  the 
molars  and  bicuspids  are  absent,  the  trituration  of  the  food  is  interfered 
with.  The  function  of  the  lost  teeth  is  partly  taken  up  by  those  which 
remain.  The  incisors  are  frequently  called  upon  to  perform  the  work  of 
the  molars  and  bicuspids,  a  service  for  which  they  are  in  no  degree 
suited,  and  one  which  ultimately  causes  them  to  be  unduly  abraded,  and 
also  results  in  an  approximation  of  the  jaws  distally ,  and  establishes  con- 
ditions which  complicate  the  subsequent  insertion  of  artificial  dentures. 
The  molar  and  bicuspid  teeth  remaining  on  one  side  of  the  mouth  may 


CHANGES  IX  JAWS  FOLLOWING    THE  LOSS  OF  TEETH.     2:35 

have  to  perform  all  the  mastication  which  should  have  been  divided 
between  the  two  sides.  This  condition  is  also  followed  bv  unnatural 
consequences,  because  the  apparatus  is  designed  for  symmetrical 
operation.  The  usual  result  is  a  distortion  of  the  normal  relation  of  the 
jaws,  and  a  movement  of  the  remaining  teeth  under  the  unnatural 
masticatory  force. 

The  assumption  of  the  whole  masticatory  function  by  a  portion  of 
the  denture  mav  continue  satisfactorilv  for  a  while,  and  the  digestive 
process  may  not  suffer,  because  in  the  alimentary  tract  there  occurs  a 
large  amount  of  adjustment  to  the  conditions  in  the  mouth  .  The 
more  slowly  the  teeth  are  lost,  the  more  readily  will  this  adjustment 
take  place.  The  food  habit  usually  alters  naturally  in  the  course  of 
the  process,  articles  requiring  little  trituration  or  those  previously  sub- 
divided being  utilized  in  increasing  proportion;  this  being  especially 
true  as  the  period  of  old  age  is  reached.  There  is  also  an  alteration  in 
the  secretions  to  harmonize  with  the  changed  conditions.  Lefoulon  has 
pointed  out  the  compensatory  increase  in  the  flow  of  saliva  which  takes 
place  at  this  time. 

It  is  evident  however  that  the  metabolic  balance  must  sooner  or  later 
be  disturbed  by  the  decline  of  the  masticatory  apparatus.  Oefele'  has 
shown  that  there  is  a  marked  failure  in  the  digestion  of  starches  by 
those  who  have  lost  their  molar  teeth,  and  Richard'  has  called  attention 
to  the  fact  that  in  some  animals,  vegetable  particles  may  go  through 
the  alimentary  canal  practically  unchanged,  unless  their  natural  pro- 
tective covering  had  been  broken  by  the  teeth. 

When  mastication  is  defective,  not  only  is  there  a  failure  to  assimi- 
late the  food,  but  since  particles  of  too  great  size  for  gastric  digestion 
are  swallowed,  peristalsis  is  delayed,  fermentation  takes  place,  and 
pathological  processes  ensue  in  the  stomach  and  intestines.  The  gas- 
tritis and  enteritis  which  are  frequently  observed  in  edentulous  patients 
give  clinical  evidence  of  the  truth  of  this  assertion;  and  the  removal  of 
the  cauise^that  is,  the  restoration  o-f  the  masticatory  function  by  the 
insertion  of  satisfactory  artificial  dentures,  is  usually  followed  by  a  disap- 
pearance of  these  conditions. 


CHANGES  IN  THE  JAWS  FOLLOWING  THE  LOSS  OF   THE   TEETH. 

The  principal  changes  which  occur  in  the  jaws  after  the  loss  of  the 
teeth  take  place  in  the  alveolar  process.  This  structure  is  developed 
with  the  teeth,  furnishes  them  with  support,  and  is  largely  resorbed 
after  they  are  lost.  When  a  tooth  of  the  permanent  denture  is  ex- 
tracted, its  socket  in  the  process  of  repair  is  partially  filled  up  with  can- 
cellated bone  tissue,  which  in  turn  becomes  covered  over  with  cortical 
bone  tissue  and  mucous  membrane.  There  is  a  resorption  of  the  mar^ 
gins  of  the  socket,  particularly  of  those  corresponding  to  the  outer  and 

1  The  Dental  Record,  Vol.  xxv.,  p.  160. 

'  De  la  prothese  dentaire.     Th^se  pour  le  doctorate  en  medicine.     Paris,  1866. 


23G 


THE  HUMAN  DEXTAL  MECHANISM. 


inner  plate,  and  a  general  rounding  and  lowering  of  the  alveolar  process, 
and  a  lo.ss  of  contour  at  this  point.  This  change  is  repeated  each 
time  a  tooth  is  lost,  so  that  after  the  loss  of  all  the  teeth,  the  alveolar 
ridge  persists  in  the  modified  form  described.     The  process  of  resorp- 


Vi'..  212 


Edentulous  U7)per  jaw, 
showing  thin  alveolar  ridge. 


Fi(..  2i:i 


E<ientulou9  upper  jai\', 
showing  flat  alveolar  ridge. 


lion  differs  somewhat  in  the  two  jaws  and  differs  in  accordance  with 
the  conditions  which  have  preceded  or  attended  the  loss  of  the  teeth. 

AMien  resorption  of  the  margins  of  the  sockets  in  the  condition  com- 
monly designated  pyorrhea  alveolaris  has  preceded  the  loss  of  the  teeth. 


Fig.  214 


Section  showing  extreme  resorption  of  the  iilveolar  ridge.      (Cryer.) 

the  alveolar  ridge  will  be  found  but  poorly  marked,  and  the  overlying 
soft  tissues  which  have  been  the  seat  of  chronic  infiammation  will  be 
found  soft  and  non-resistant.  This  furnishes  the  poorest  base  for  an 
artificial  plate  denture. 


CHANGES  IN  JAWS  FOLLOWING    THE  LOSS   OF  TEETH.      287 

The  Upper  Jaw. — After  the  loss  of  the  teeth  the  maxilla  undergoes 
change  in  form  and  size.  Most  of  the  resorption  of  the  alveolar  process 
takes  place  at  the  expense  of  the  external  plate,  the  internal  plate  being 
modified  only  as  resorption  of  the  top  of  the  ridge  proceeds.  The  re- 
sorption of  the  external  portion  of  the  ridge  generally  occurs  progres- 
sively.    The  ridge  becomes  more  rounded,  lower,  and  gradually  less  pro- 


Section  showing  considerable  resorption  of  the  alveolar  ridge.      (Cryer.) 

nounced.  (Fig.  215.)  Wlien  the  alveolar  process  was  originally  high 
and  narrow,  the  resorption  of  the  external  plate  reduces  its  thickness 
and  it  persists  as  a  thin  well-marked  ridge.  (Figs.  212  and  216.) 
The  ultimate  state  which  the  jaw  may  reach  is  that  in  which  the  whole 
roof  of  the  mouth  is  flat.  (Figs.  213  and  214.)  This  occurs  only 
in  unusual  cases.  In  extreme  cases  there  is  a  falling  in  of  the  cartilag- 
inous septum  of  the  nose  from  the  resorption  anteriorly.      (Fig.  217.) 

Fig.  216  Fig.  217 


Profile  view  of  edentulous  upper  jaw, 
showing  thin  alveolar  ridge. 


Profile  view  of  edentulous  upper  jaw, 
showing  considerable  resorption. 


The  palatal  vault  is  the  part  of  the  jaw  in  which  the  least  change 
occurs,  as  the  resorption  takes  place  on  the  external  side  of  the  ridge 
and  on  top.  This  maybe  noted  by  reference  to  Fig.  213,  which  shows 
an  edentulous  jaw.  When  this  is  compared  with  one  with  the  full  com- 
plement of  teeth  (Fig.  187),  reference  to  the  anterior  palatine  foramen, 
die  position  of  which  does  not  change  after  the  loss  of  the  teeth,  and 
which  in  the  living  subject  corresponds  approximately  to  the  incisive 


238  THE  HUMAN  DENTAL  MECHANISM. 

pad  of  the  rufj.T,  will  show  that  most  of  the  resorption  lias  occurred 
external  to  this  point. 

The  extreme  degrees  of  resorption  of  the  proct\ss  are  caused  by 
stimulation  of  the  giant  cells  from  pressure  in  masticating  die  food 
directly  upon  the  guiiLS,  from  ill-fitting  dentures,  or  from  other  causes. 
Properly  fitting  artificial  dentures  prevent,  in  a  great  measure,  diis  re- 
sorption. Artificial  dentures  arrarged  with  occlusion  at  one  point  only 
are  frequently  productive  of  a  localized  resoi-j^tion  of  the  process,  which 
complicates  the  successful  fitting  of  new  dentures.  One  of  the  most 
commonly  observed  cases  of  this  sort  is  that  in  which  a  full  upper  plate 
denture  is  antagonized  only  by  the  six  or  eight  lower  natural  anterior 
teeth,  there  being  no  teeth  posterior  to  this  })oint,  resorption  of  the 
alveolar  process  of  the  maxilla  in  front  occurring  as  the  result  of  the 
undue  pressure  upon  it. 

The  Lower  Jaw. — ^The  changes  occurring  in  the  alveolar  process  of 
the  lower  jaw  are  similar  to  those  which  occur  in  the  upper.  In  dis- 
cussing the  phenomena  of  growth  and  resorption  in  the  mandible,  the 

Fio.  218 


Internal  view  of  the  half  ot  an  edentulous  mandible,  showing  character  of  the  resorption  of  the 
alveolar  process.  There  is  considerable  resorption  posteriorly,  but  very  little  in  the  anterior  portion 
of  the  process,  as  the  teeth  have  been  lost  here  only  a  short  time. 

character  and  extent  of  these  changes  are  well  described  by  Sir  John 
Tomes  as  follows:  "In  the  great  majority  of  specimens  a  small  fora- 
men is  situated  in  the  median  line  immediately  above  the  upper  pair 
of  tubercles  (genial),  and  when  present, this  may  be  selected  as  a  point 
from  which  to  take  *  *  *  *  dimensions.  Unfortunately  it  is  some 
times  wanting  or  is  represented  by  a  similar  aperture  below  the  spinse 
mentales.  In  a  series  of  jaws  taken  from  very  old  subjects  in  whom 
the  teeth  had  been  lost  and  the  alveolar  process  had  been  absorbed 
the  foramen  holds  to  its  original  position.  If  these  specimens  are  sub- 
jected to  measurement  we  find  that  this  aperture  is  within  tV  to  fr 
of  an  inch  of  the  alveolar  margin,  showing  a  loss  in  the  oldest  jaw  of 
tV  while  it  is  separated  from  the  lower  border  of  the  jaw  by  yy  of 
aninch,the  lossinthis  direction  being  inappreciable."  (Fig.  218.)     The 


CHAXGES  IX  JAWS  FOLLOWING    THE  LOSS  OF  TEETH.       289 

alveolar  plates  of  the  mandible,  accordincr  to  Cryer,  resorh  more  evenly 
than  in  the  upper  jaw,  usually  a  small  ridge  remaining  to  indicate  the 
position  of  the  former  process  and  teeth.  The  external  oblique  line 
which  descends  from  the  anterior  margin  of  the  coronoid  process,  is, 
alwavs  external  to  the  location  of  the  former  alveolar  ridge.     In  cases 


Fio.  219 


Specimens  showing  the  angle  formed  by  the  ramus  and  the  body  of  the  mandible;  A,  at  ths 
time  of  completion  of  the  temporary  denture;  B,  in  adult  life:  C,  in  old  age.  (.From  a  photograph 
of  specimens  in  the  Wistar  Institute  of  Anatomy.) 

of  extreme  resorption  the  ridge  is  entirely  obliterated,  and  commonly 
there  is  less  ridge  in  the  lower  jaw  than  in  the  upper. 

Only  slight  change  occurs  in  the  body  of  the  bone,  as  has  been  men- 
tioned above.  A  noticeable  change,  however,  occurs  at  the  angle  of  the 
jaw.  Fig.  219  illustrates  the  cycle  of  change  occurring  in  this  region 
between  the  time  of  the  completion  of  the  temporary  denture  and  old 
acre.  Since  the  vertical  distance  betv.-een  the  jaws  is  increased  in  adult 
life  to  accommodate  the  permanent  denture^  there  must  necessarily  be  a 


240 


THE  HUMAN  DENTAL  MECHANISM. 


chanfrp  in  the  anf>;lc  of  the  jaw  to  make  this  possible.  The  average 
angle  made  by  the  body  and  ramus  of  the  jaw  in  an  adult  is  about  ]20°. 
While  the  natural  teeth  are  in  position,  no  change  occurs  in  the  rela- 
tion of  the  jaws  except  a  slight  approximation  due  to  the  wear  of  the  teeth. 
If  the  teeth  remained  there  would  be  no  a])preciable  alteration  of  the 


Fig.    220 


Stull  showing  relation  of  edentulous  jaws:  profile  view.  (From  photograph  of  a  specimen  in  the 
collection  of  Dr.  M.  H.  Cryer.) 


r 

Fig.  221 
4         "a 

] 

k 

i 

Skull  Hhowinj:  relation  of  edentulous  jaws;  views  from  below.  From  photograph  of  a  specimen 
in  the  collection  of  Dr.  M.  H.  Cryer.) 


angle  of  the  jaw.  As  age  advances  and  as  the  back  teeth  are  lost,  the 
powerful  traction  exerted  by  the  muscular  apparatus,  upon  the  ana- 
tomical angle  of  the  jaw,  the  forward  end  of  the  jaw  being  in  occlu- 
sion through  the  anterior  teeth,  causes  a  flattening  of  the  angle  and 
at  the  same  time  the  symphysis  is  carried  forward.  After  all  the  teeth 
are  lost  this  becomes  still  more  evident.     Slisrht  cliange  occurs  also  at 


VOICE  AND  SPEECH.  241 

the  condyle  where  ti  general  flattening  takes  place.  There  is  also  an  alter- 
ation of  the  glenoiti  fossa  corresponding  to  this.  Its  pronounced  mar- 
gin is  lostandit  becomes  in  generahnore  flattened.  (Fig.  175  D  and  E.) 
The  Relation  of  the  Jaws. — "As  the  resorption  of  the  alveolar  process 
goes  on,  the  vertical  distance  between  the  body  of  the  lower  jaw  and  that 
of  the  upper  is  lessened  while  the  natural  difference  in  their  width  is  in- 
creased. The  area  of  the  upper  jaw  becomes  smaller  in  proportion  to 
that  of  the  lower;  the  axes  of  the  mandible  extending  further  outward. 
'  In  the  endeavor  to  close  the  jaws  under  these  circumstances,  the  lower 
is  projected  further  forward  as  it  rises  to  meet  the  upper,  until  in  extreme 
cases,  it  may  pass  absolutely  outside  of  the  upper.^"  Figs.  220  and  221 
give  two  views  of  an  edentulous  skull  and  show  the  relations  of  the 
jaws. 

VOICE  AND  SPEECH. 

Voice. — Voice  is  the  audible  sound  originating  in  the  vibrations  of 
the  vocal  cords  and  reinforced  by  the  resonance  of  air  cavities  situated 
in  the  head  and  chest.  The  apparatus  by  which  it  is  produced  consists 
of  (1)  the  lungs,  chest  walls,  and  muscles  of  expiration,  which  furnish 
the  motive  power;  (2)  the  larnyx,  in  which  are  situated  the  vocal  cords; 
and  (3)  the  chest  cavity  below,  and  pharynx,  mouth  and  nose  above, 
which  constitute  the  resonating  chambers.  When  the  air  is  forced 
out  of  the  lungs  by  the  contraction  of  the  chest  muscles  and  at  the  same 
time  the  vocal  cords  are  approximated  and  made  tense,  their  edges  are 
set  in  motion  and  a  sound  is  emitted.  The  cords  themselves  are 
capable  of  producing  only  a  feeble  sound/  but  when  they  vibrate  close 
to  self-sounding  bodies  as  the  air  in  the  cavities  above  mentioned,  this 
air  is  thrown  into  sympathetic  vibration  and  the  volume  and  character 
of  the  original  sound  are  altered.  The  sound  made  by  the  cords  is 
not  a  simple  musical  tone  but  is  a  complex  "note  made  up  of  a  funda- 
mental tone  combined  with  upper  partial  tones,"  overtones,  or  harmon- 
ics, of  which  as  many  as  sixteen  in  some  instances  accompany  the  fun- 
damental.^ When  the  air  contained  in  the  resonant  cavities  is  thrown 
into  vibration,  it  is  capable  of  emitting  a  musical  note,  the  pitch  of 
which  depends  either  upon  the  size  of  the  cavity  or  upon  the  size  of  the 
opening  by  which  it  communicates  with  the  external  air.  The  larger 
the  cavity  or  the  smaller  its  opening,  the  lower  wall  be  the  pitch  and  vice- 
versa.  The  resonant  cavities  reinforce  either  the  fundamental  tone, 
or  the  harmonic  of  the  laryngeal  sound,  which  corresponds  to  the 
pitch  to  w^hich  they  are  tuned,  so  that  alterations  in  their  shape  largely 
determine  what  is  known  as  the  quality  of  the  voice. 

The  voice  possesses  in  common  with  other  musical  sounds  three 
characteristics — (1)  pitch,  (2)  loudness,  and  (3)  quality.  The  pitch  is 
determined  by  the  tension  of  the  vocal  cords;  the  tighter  they  are 
stretched  the  higher  will  be  the  pitch.  Loudness  is  proportional  to  the 
strength  of  the  expiratory  blast,  and  is  also  related  to  the  resonance 

i  M.  H.  Cryer.     Internal  Anatomy  of  the  Face.  p.  168 

^  Sewall:    American  Text  Book  of  Physiology,  Vol.  II.,  p.  421. 

^  Helmhoitz— Quoted  by  Sewall:  American  Text  Book  of  Physiology  Vol.  II.   p.  435. 

16 


242  THE  HUMAX  DENTAL  MECHANISM. 

of  the  cavities  above  and  below  the  larynx.  The  quality  of  the  voice 
is  dependent  upon  the  charaeter  or  form  of  the  sound  wave,  and  is  re- 
lated to  the  number  and  relative  intensity  of  the  overtones  or  harmonics 
which  accompany  the  fundamental  tone.  The  form  of  the  wave  is 
determined  by  the  state  of  tension  of  the  vocal  cords,  and  by  the 
form  and  size  of  the  air  cavities,  which  act  as  the  resonating  cham- 
bers. The  air  cavities,  whose  pitch  may  be  changed  at  will,  contribute 
by  their  resonance,  now  to  reinforce  this  tone  and  now  that,  so  that  any 
overtone  or  the  fundamental  may  be  intensified  by  change  in  the  shape 
of  the  resonant  cavities. 

The  sesthetic  value  of  a  human  voice  depends  upon  the  number, 
character,  and  relative  intensity  of  the  overtones  which  accompany  its 
fundamental  tone.  This  tone-quality  is  determined  by  the  power  of 
adjustment  of  the  larynx,  in  which  the  tones  are  produced,  and  by  the 
precision  of  the  muscular  adjustments  regulating  the  resonant  pitch 
of  the  air  cavities  in  which  the  tones  are  accentuated.  The  capability  of 
the  larynx  is  the  more  important  of  these  factors,  but  it  is  evident  that 
ability  to  correctly  attune  the  resonating  chambers  is  a  necessary  adjunct. 

The  mouth  is  one  of  the  most  important  of  these  resonant  cavities. 
Its  form  is  altered  by  the  depression  of  the  mandible  and  by  the  move- 
ments of  the  tongue.  The  soft  palate  also  assists  in  this  process,  its 
chief  function,  however,  being  to  separate  the  mouth  and  nose  cavities. 
Increase  in  the  size  of  the  mouth  causes  a  corresponding  lowering  of 
its  pitch.  The  lips  serve  to  increase  or  diminish  the  opening  communi- 
cating with  the  outside  air;  the  larger  the  opening,  the  higher  will  be 
the  fundamental  note  of  the  cavity;  the  smaller  the  opening,  the  lower 
will  be  the  note. 

The  pharynx  is  changed  in  shape  by  the  rising  and  falling  of  the 
larynx,  while  the  resonance  of  the  nasal  chambers  and  the  air  cells 
communicating  therewith  cannot  be  altered  at  will.  The  resonance 
of  these  cavities  may  be  controlled  only  as  they  are  added  to  or  sepa- 
rated from  the  mouth  space  by  the  action  of  the  soft  palate  and  tongue. 

Those  portions  of  the  air  cavities  which  are  uninfluenced  by  muscu- 
lar action  are  but  passive  factors  in  regulating  their  resonance.  It 
is  by  the  adjustment  to  these  of  the  soft  and  moveable  parts  that 
variations  in  their  resonance  are  produced.  Therefore  the  change  in 
the  fixed  parts  of  the  mouth  caused  by  the  loss  of  the  teeth,  necessitates 
a  change  in  the  muscular  adjustments,  and  requires  new  co-ordinations 
on  the  part  of  the  tongue.  The  lips  and  cheeks,  which  are  no  longer 
supported  by  the  teeth,  fall  in  and  complicate  the  process  of  adjust- 
ment. This  change  in  the  fixed  portion  of  the  mouth  is  almost  al- 
ways succeeded  by  changes  in  the  qualities  of  the  voice,  although  the 
speaking  voice  is  altered  less  than  the  singing  voice,  in  which  more 
precise  muscular  co-ordination  is  required. 

Speech. — Articulate  speech  by  means  of  which  man  communicates 
his  thoughts,  has  for  a  long  time  been  divided  by  scholars  into  vowel 
sounds,  or  those  produced  in  the  larynx  and  modified  by  the  position  of 
the  various  mouth  parts,  and  consonant  sounds,  which  are  noises  ac- 


VOICE  AND  SPEECH. 


243 


companying  the  other  sounds  and  are  largely  made  in  the  mouth. 
Language  consists  in  the  regular  progression  of  these  sounds,  which 
either  singly  or  in  combination  represent  ideas. 

Vowels.— The  vowels  are  the  true  laryngeal  sounds,  originating  in  the 
vibration  of  the  vocal  cords  and  determined  by  their  state  of  tension  and 
by  the  peculiar  resonance  of  the  pharynx,  nose  and  mouth.  For  any 
given  vowel  the  posture  of  the  mouth  parts  is  the  same,  that  is,  this 
cavity  is  tuned  to  a  definite  pitch,  the  difference  in  the  actual  pitch  of  the 
vowel  being  determined  by  the  tension  of  the  vocal  cords  and  by  the  size 
of  the  pharynx.  In  tuning  the  cavity  for  the  sounding  of  ah  (father),  o 
(oivti),  and  oo  (shoot),  the  tongue  does  not  touch  the  palatal  vault,  but 
in  a  (ate)  and  e  (met),  its  sides  touch  the  molar  and  bicuspid  teeth  and 
adjoining  alveolar  process.  The  vowels  are  closely  related,  for  the 
position  of  the  mouth  parts  for  one  vowel  easily  changes  to  that  for 
another.  It  is  evident  therefore  that  the  changed  conditions  of  the 
mouth  incident  to  the  loss  of  the  teeth  require  new  muscular  adjust- 
ments to  enable  the  mouth  cavity  to  be  tuned  to  the  proper  pitch  for 
each  vowel. 

Consonants. — In  the  production  of  most  of  the  consonant  sounds, 
a  current  of  air  is  interrupted  or  stopped  at  some  point  during  its  exit 
from  the  lungs,  the  noise  resulting  therefrom  being  the  consonant  sound. 
Some  consonants  however  may  be  sounded  only  in  conjunction  with  a 
vowel,  in  which  case  the  consonant  is  only  a  superadded  noise  to  the 
laryngeal  sound  and  is  due  to  the  peculiar  resonance  imparted  by  the 
mouth  and  nose  cavities  when  they  are  properly  disposed  for  the  for- 
mation of  the  consonant.  In  other  consonants  the  sound  originates 
in  the  mouth,  from  vibration  of  the  mouth  parts  caused  by  an  in- 
complete obstruction  to  the  air  current,  while  in  others  there  is  an  ex- 
plosive sound  due  to  the  sudden  stoppage  or  starting  of  the  air 
current. 

The  following  table^  gives  a  classification  of  the  consonants  accor- 
ding to  the  place  at  which  they  are  formed : 


Oral 

Nasal 

Place  of  articulation 

Momentary 

Continuous 

Continuous 

Surds 
without 
voice 

Sonants 
with 
voice 

Surds 

without 

voice 

Surds 
with 
voice 

Sonants 
with 
voice 

b 

w 

m 

f 
th  (in) 
s,  c  (ity) 

V 

th  (y) 

Tongue  and  hard  palate  (forward).. 

t 

d 

z,  r 

n 

Tongue  and  hard  palate  (back)  .... 

ch 

J 

sh 

z,  r 

Tongue,  hard  palate  and  soft 





y.l 

k,  c  (at) 

g 





ng 

*  Sewall:   American  Text  Book  of  Physiology,  Vol  11..  p.  437. 


244 


THE  HUMAN  DENTAL  MECHANISM. 


A  careful  study  of  this  table  will  show  that  the  factors  determining 
any  given  consonant  are  the  strength  of  the  expiratory  blast,  the  pres- 
ence or  absence  of  voice,  and  the  position  of  the  mouth  parts. 

Mechanism  of  the  Production  of  the  Consonant  Sounds. — In  the  for- 
mation of  the  P  and  B  sounds,  the  air  blast  meets  no  interference  in 
the  mouth  because  of  a  narrowing  of  the  channel,  but  is  interrupted  at 
the  lips  by  their  sudden  opening  or  closure  (Fig.  222).  In  P  there  is 
greater  air  pressure  and  greater  suddenness  in  the  stoppage  or  startin  g 
of  the  current.  In  K  and  (i  also  the  channel  is  unaltered,  stoppage  of 
the  blast  occurring  at  the  posterior  portion  of  the  palatal  vault  by  the 
application  of  the  base  of  the  tongue  to  the  soft  palate.  In  G  the 
air  pressure  is  not  so  great  as  in  K  and  the  tongue  touches  a  larger 
area.  In  L  and  ^I  and  NG  the  channel  is  not  changed  by  the  appli- 
cation of  the  sides  of  the  tongue  to  the  vault.  In  L  the  tip  of  the 
tongue  touches  the  process  back  of  the  incisors,  while  the  air  current 
divides  and  escapes  around  its  sides.  In  M  and  NG  the  air  current 
escapes  through  the  nose. 


Fig.  222 


T&DTh 


>  K&e 


1.  LMagraramatiu  drawing  showing  plac«  of  articulation  of  the  consonant  sounds.  2. 
Drawing  showing  contact  with  the  tongue  with  molars  and  bicuspids  in  the  formation  of 
certain  consonants. 


In  all  the  other  consonant  sounds  except  H,  an  air  channel  is  made 
by  means  of  the  tongue  to  direct  the  blast  either  upon  some  point  at 
which  there  is  a  partial  obstruction  or  upon  some  point  at  which  it 
is  stopped.  For  this  purpose  the  tongue  is  applied  to  the  sides  of  the 
palatal  vault  touching  the  molar  and  bicuspid  teeth  and  the  process  ad- 
joining, and  forms  a  sort  of  gutter  through  which  the  air  is  expelled. 
The  position  and  area  of  this  contact  varies  with  the  different  letters. 
In  the  formation  of  T  and  D  the  lips  are  open  and  the  tongue  touches 
the  alveolar  border  with  its  tips  and  sides,  the  tip  being  depressed  as 
the  current  of  air  is  ejected.     In  T  the  pressure  of  the  blast  is  greater 


VOICE  AND  SPEECH.  245 

than  in  D.  In  CII  and  J  the  tongue  is  pressed  upon  the  alveolar 
border  at  its  sides  and  tip,  and  the  air  current  is  forced  between  the  tip 
and  the  anterior  portion  of  the  palate.  The  noise  is  made  between  the 
palate  and  the  tip  of  the  tongue. 

In  N  the  oral  cavity  is  closed  by  the  placing  of  the  tip  of  the  tongue 
against  the  palate  instead  of  by  the  closure  of  the  lips  as  in  M.  The 
air  escapes  through  the  nose  in  these  consonants,  and  a  peculiar  nasal 
resonance  is  added  to  the  voice  sound. 

In  articulating  the  sounds  S,  Z,  Th,  Sh,  Zh,  F  and  V  the  air  current 
produces  a  blowing  sound  due  to  its  impingement  upon  some  portion  of 
the  channel.  In  the  F  and  V  sounds  the  lower  lip  is  in  contact  with 
the  incisal  edges  of  the  upper  teeth,  the  tip  of  the  tongue  being  pressed 
against  the  lower  incisors,  while  its  sides  touch  the  last  molar  teeth  and 
process,  and  guide  the  air  between  the  lip  and  teeth.  In  the  formation 
of  S  the  air  is  forced  past  an  incomplete  obstruction,  the  edges  of 
the  adjacent  tissues  being  set  in  vibration  by  the  current.  The  teeth 
are  almost  in  contact,  the  lips  slightly  open,  the  tongue  curls  upon  the 
sides  to  touch  the  molar  and  bicuspid  teeth  as  far  forward  as  the 
canine  and  the  adjoining  palatal  vault,  leaving  a  narrow  opening 
in  front  for  the  egress  of  the  air.  The  end  of  the  tongue  touches 
the  lower  incisor  teeth,  and  the  sound  is  caused  by  the  impingement  of 
the  air  upon  the  edges  of  the  closed  teeth.  Z  and  C  (soft  as  before  E 
and  I)  are  made  in  the  same  way,  the  difference  in  the  intensity  of  the 
blast  differentiating  them. 

In  Sh  and  Zh  the  air  is  forced  by  two  obstructions,  one  caused  by  the 
arching  up  of  the  tongue  to  nearly  touch  the  palate,  the  other  caused 
exactly  as  in  S.    X  is  a  combination  of  theS  and  K  sounds. 

In  Th  the  tip  of  the  tongue  is  placed  betw^een  the  upper  and 
lower  incisors,  the  air  channel  being  formed  by  its  sides  as  in  some 
other  consonants.  The  edges  of  the  upper  teeth  are  set  in  vibration 
by.  the  air. 

"Lingual  R"  is  produced  by  having  the  sides  of  the  tongue  in  contact 
with  the  molar  teeth  and  palate,  to  direct  the  current  upon  the  tip  of 
the  tongue  w^hich  is  curved  upward  toward  the  palate  and  thrown  into 
irregular  vibrations  by  the  blast. 

In  H^  the  air  current  meets  no  obstruction  in  the  mouth,  the  vibra- 
tions producing  the  sound  of  the  consonant  being  those  of  the  separated 
vocal  cords.  As  W  is  a  combination  of  H  and  V,  its  production  needs 
no  separate  description. 

The  above  description  is  that  of  the  method  of  producing  these  sounds 
when  the  apparatus  is  in  its  normal  state.  A  change  in  any  of  the  parts 
concerned  in  this  process  must  result  in  an  interference  with  the  correct 
articulation  of  the  sounds. 

It  will  be  seen  that  so  far  as  the  part  taken  by  the  mouth  in  the  pro- 
duction of  these  sounds  is  concerned,  interference  with  the  mechanism 
by  w^hich  the  air  channel  for  a  given  consonant  is  formed,  or  v^dth  that 
by  which  the  air  is  obstructed  or  stopped,  must  necessarily  be  followed 

1   Sewall,  op.  cit.,  p.  438- 


246  I'H^  HUM  AX  DENTAL  M  ECU  AX  ISM. 

by  an  interference  with  the  proper  articulation  of  that  sound.  The 
channel  is  formed  by  the  adjustment  of  the  tongue  to  the  teeth  and 
the  sides  of  the  palatal  vault,  and  the  obstructions  and  interruptions  are 
made  through  contact  of  the  tongue  with  the  teeth,  or  the  hard  or  soft 
palate,  or  of  the  lips  with  each  other,  or  with  the  teeth.  The  loss  of 
the  teeth,  the  resorption  of  the  process,  which  alters  the  form  of  the 
palatal  vault,  and  the  change  in  the  relation  of  the  jaws  must  all  have  a 
serious  influence  upon  articulation.  This  is  also  comj)licated  by  the  fall- 
ing in  of  the  lips  and  cheeks  which  are  supported  by  the  teeth  and  al- 
veolar process.  The  tongue  is  the  principal  organ  of  articulation  and 
may  learn  to  accommodate  itself  greatly  to  the  change  in  the  parts  to 
which  it  is  applied  in  the  production  of  the  sounds,  but  it  is  evident  in 
some  instances  that  satisfactory  adjustment  cannot  take  place. 

The  loss  of  the  incisor  teeth  aft'ects  the  sounds  articulated  in  this 
region.  When  a  single  upper  incisor  is  missing,  at  thl.^  point  there  is 
an  escape  of  air  in  some  of  the  co-ordinations  in  which  it  should  be  con- 
fined, and  the  sound  of  S  seems  to  be  made.  One  of  the  commonest 
defects  from  absence  of  the  incisors  is  in  the  formation  of  Th,  the  air 
escaping  and  giving  an  S  sound  instead.  When  the  upper  incisors 
are  lost,  the  F  and  V  sounds  are  difficult  to  make,  the  lower  lip 
having  to  accommodate  itself  to  the  alveolar  process  or  to  the  upper 
lip,  and  the  sound  approximating  P  or  B.  In  some  cases  the  S  sound 
itself  is  diflicult,  especially  if  both  upper  and  lower  incisors  are  missing, 
Sh  and  Zh  being  similarly  affected  by  this  condition.  T  and  D  are  also 
sometimes  difficult  to  enunciate,  especially  if  there  has  been  much  resorp- 
tion of  the  alveolar  process  against  which  the  tip  of  the  tongue  presses. 

As  the  molar  and  bicuspid  teeth  and  adjoining  process  form  part 
of  the  lateral  walls  of  the  air  channel  in  the  enunciation  of  a  number 
of  consonants,  deficiencies  here  affect  speech  also.  The  tongue 
cannot  close  the  sides  of  the  air  passage,  and  the  current  escapes  into 
the  cheeks.  T,  D,  Ch,  T,  Th,  Sh,  Zh,  S,  Z  and  C  are  principally 
affected  and  especially  so  when  followefl  by  the  vowels  A  or  E,  con- 
tact of  the  tongue  with  the  sides  of  the  vault  being  also  necessary 
in  the  making  of  these  vowel  sounds.  F  and  V  may  occasionally 
suffer,  and  sometimes  the  tongue  cannot  shut  off  the  air  in  N  and  it 
escapes  into  the  mouth,  destroying  the  full  nasal  resonance  character- 
istic of  this  letter. 

THE  EXPRESSION  OF  IDEAS  AND  EMOTIONS  BY  THE  FACE. 

The  expression  of  thought  and  feeling  in  man  is  accomplished  for 
the  most  part  in  three  ways:  by  gesture,  by  speech  and  by  wTiting. 
Speech  is  the  means  in  most  universal  use,  gesture  being  chiefly  employed 
to  supplement  language,  while  the  utility  of  WTiting  is  naturally  re- 
stricted because  of  the  conditions  required  for  its  performance.  Be- 
side containing  the  organs  of  articulate  speech,  the  face  performs  ex- 
pressional  services  which  are  not  included  under  any  of  the  above 
headings.  These  consist  of  the  movements  of  associated  groups  of 
facial  muscles  which   occur    simultaneous  with  the  existence  of  cer- 


EXPRESSION  OF  IDEAS  AND  EMOTIONS.  947 

tain  emotions  or  which  express  some  idea  of  the  mind.  The  muscu- 
hir  niovemcnts  and  the  etl'ect  they  produce  upon  the  countenance  are 
the  accompaniment  and  the  outward  manifestation  of  the  psychic  state. 
Accorchng  to  Mantegazza^  they  have  two  diverse  functions;  they 
may  replace  or  conn)lete  hmguage,  or  they  may  defend  the  nerve  cen- 
tres or  the  parts  of  the  body  against  dangers  of  different  kinds.  The 
forms  of  facial  expression  are  the  same  throughout  the  world  ^  and 
are  too  familiar  to  require  description. 

As  one  of  the  most  mobile  features  of  the  face,  the  mouth  partici- 
pates largely  in  its  expressive  movements.  The  loss  of  the  teeth  in- 
terferes with  the  performance  of  this  function  of  the  mouth;  it  is  pro- 
posed therefore  to  give  a  brief  account  of  the  mechanism  by  which  the 
facial  movements  are  effected,  to  point  out  the  part  taken  by  the  mouth, 
and  to  indicate  in  what  way  the  absence  of  the  teeth  interferes  with 
the  muscular  action. 

Before  discussing  this  mechanism,  however,  it  will  be  necessary  to 
clearly  differentiate  between  the  terms  "facial  expression"  and  "the 
expressive  movements  of  the  face."  The  former  alludes  to  the  coun- 
tenance, its  form,  contours,  surface,  muscles — in  short,  its  anatomy; 
while  the  latter  refers  to  the  contraction  of  the  facial  muscles  which 
produces  the  movements  expressive  of  ideas  and  emotions.  Facial 
expression  will  be  treated  under  a  separate  heading. 

The  Facial  Mechanism  of  Expression. — The  mechanism  of  the  expres- 
sional  movements  of  the  face  consists  of  (1)  a  bony  framework,the 
facial  skeleton;  (2)  the  muscular  apparatus,  technically  referred  to  as 
the  muscles  of  expression;  (3)  the  connective  tissue,  fat,  and  over- 
lying integument  which  complete  the  face. 

The  facial  portion  of  the  skull  gives  form  to  the  countenance.  It 
also  contains  some  of  the  special  sense  organs  which  are  features  of 
the  face,  and  it  affords  points  of  origin  for  the  muscles  of  expression. 
The  skin  of  the  face  is  very  thin,  elastic,  and  loosely  adherent  to  the 
underlying  structures.  Over  the  nose,  however,  it  closely  adheres  to 
the  bone  and  cartilage,  and  over  the  chin  it  is  closely  united  to  the 
mandible  through  the  medium  of  the  intervening  tissue.  The  super- 
ficial fascia  underlying  the  skin  is  intimately  united  to  it.  It  is  very 
loose  and  cellullar,  contains  large  amounts  of  fat,  and  permits  great 
mobility  of  the  integument.  The  facial  muscles,  illustrated  in  Fig.  223, 
are  numerous.  For  the  most  part  they  aie  superficial  and  are  closely 
attached  to  the  under  surface  of  the  skin.  This  arrangement  permits 
them  to  produce  in  the  skin  the  folds  and  depressions  associated  with 
their   movements. 

The  facial  muscles  of  expression  (Fig.  223)  may  be  divided  into  three 
groups — those  centering  about  the  eye,  about  the  ala  of  the  nose,  and 
about  the  mouth.  They  are  all  concerned  in  the  expressive  move- 
ments of  the  face,  but  as  we  are  interested  only  in  the  part  played  by 
the  mouth,  we  shall  discuss  only  the  muscles  operating  in  this  region. 

^  Physiognomy  and  Expression,  p.  80. 

"  Charles  Darwin:  The  Expression  of  the  Emotions  in  Man  and  Animals. 


248 


THE  HUMAN  DENTAL  MECHANISM. 


The  orbicularis  oris  which  surrounds  the  aperture  of  the  mouth  is 
the  common  meeting  ground  of  the  muscles  of  this  group.  It  consists 
of  two  portions — the  labial,  which  occupies  the  red  border  of  the  lip, 
and  is  narrow,  thick,  and  regular,  and  the  facial,  which  iswiderand 
thinner,  antl  spreads  out  into  a  wide  band  just  beneath  the  skin  around 
the  oral  orifice.  Joining  these  two  portions  are  a  large  number  of  mus- 
cular fibres  which  run  antero-posteriorly  from  the  skin  on  the  outside 
to  the  mucous  membrane  on  the  inside.  This  muscle  constitutes 
the  larger  portion  of  the  substance  of  the  lips,  and  gives  them  their 


Fig.  223. 


The  facial  muscles  of  expression. 

fleshy  characteristics.  The  labial  portion  of  the  orbicularis  has  no 
attachment  to  the  bone  beneath  it.  At  the  angle  of  the  mouth  it  is 
deeply  situated  and  intimately  connected  with  the  buccinator  muscle, 
decussating  fibres  of  which  pass  above  and  below  this  point  to  be  lost 
in  the  upper  and  lower  lip.  The  facial  portion  has  only  three  small 
bonv  attachments  on  each  side.  The  largest  of  these  are  the  naso- 
labial slips,  which  are  slender  bands  passing  up  to  be  attached  to  the 
anterior  nasal  spines,  and  which  correspond  on  the  external  surface  to 
the  philtrum.  Two  other  slips  are  attached  to  the  incisive  fossa?  in 
the  upper  jaw,  and  two  smaller  slips  are  inserted  in  the  incisive 
fossse  of  the  mandible.     The  orbicularis  is  not  truly  speaking  a  sphinc- 


EXPRESSION  OF  IDEAS  AND  EMOTIONS.  249 

ter  muscle  as  that  term  is  applied  to  orificial  muscles  of  other  parts  of 
the  body.  It  is  doubtful  if  any  of  its  fibres  are  continuous  around 
the  aperture.  When  the  labial  portion  alone  contracts,  it  everts  the 
lips  and  diminishes  the  width  of  the  mouth.  The  facial  portion  serves 
to  press  the  lips  against  the  teeth  and  adjoining  process.  Its  two  por- 
tions oppose  the  other  mouth  muscles. 

Arranged  radially  about  the  mouth  and  united  to  the  orbicularis  are 
the  other  muscles  of  this  group.  They  are  the  levator  labii  superioris 
aheque  nasi,  the  levator  labii  superioris  proprius,  the  levator  anguli 
oris,  the  zygomaticus  major,  the  zygomaticus  minor,  the  depressor 
anguli  oris,  the  depressor  labii  inferioris,  the  levator  labii  inferioris 
and  the  risorius. 

The  points  of  origin  from  the  bones  of  the  face  and  the  points  of  at- 
tachment to  the  orbicularis  indicate  the  line  of  action  of  these  muscles. 
The  anterior  teeth  and  alveolar  process  form  a  base  upon  which  the 
tissues  of  the  lips  may  be  moved  by  them.  The  mucous  membrane  is 
lubricated  by  the  saliva  and  permits  an  easy  sliding  of  the  lips  upon  the 
underlying  structures.  The  canine  tooth  and  eminence  are  especially 
important  as  a  base  of  support  for  these  movements.  They  underlie 
the  corner  of  the  mouth  and  afford  a  prominence  over  which  the  lips 
may  be  pulled  by  the  muscles  attached  to  the  angle  of  the  mouth. 

The  action  of  the  individual  muscles  constituting  this  group  has  been 
carefully  investigated  by  Duchenne  ^  who  has  given  a  detailed  account 
of  their  effect  upon  the  countenance.  It  is  beside  the  purpose  of  this 
work  to  discuss  the  significance  of  these  movements  in  great  detail. 
The  reader  is  referred  to  the  literature  on  the  subject  for  more  minute 
particulars.  In  order,  however,  that  the  reader  may  understand  the 
usual  meaning  of  the  contraction  of  these  separate  muscles  the  following 
account  of  their  action  is  appended. 

The  levator  labii  superioris  alsequse  nasi  is  the  principal  muscle  in  the 
expression  of  contempt  and  disdain.  It  dilates  the  nostrils  and  raises 
the  upper  lip  and  draws  it  slightly  forward,  and  with  the  other  levator 
muscles  increases  the  prominence  of  the  cheek  below  the  orbit.  It 
helps  to  develop  the  naso-labial  fold.  When  it  contracts  with  the  other 
levator  muscles  of  the  upper  lip,  an  appearance  of  sadness  and  grief  is 
produced.  The  levator  anguli  oris  draws  up  the  angle  of  the  mouth, 
pushing  up  the  lower  eyelid  as  in  crying.  The  zygomaticus  major  is 
the  muscle  of  joy  or  laughter.  It  draws  the  corner  of  the  mouth  back- 
ward and  a  little  upward.  The  zygomaticus  minor  assists  in  drawing 
upward  and  outward  and  backward  the  outer  corner  of  the  upper  lip 
but  not  the  corner  of  the  mouth.  It  produces  an  expression  of  sadness. 
The  depressor  anguli  oris  (triangularis  menti)  draws  the  corner  of  the 
mouth  backward  and  downward  and  is  necessary  in  the  expression  of 
sadness  or  grief.  The  depressor  labii  inferioris  (quadratus  menti)  draws 
the  lower  half  of  the  lower  lip  downward  and  a  little  outward.  With  its 
fellow  of  the  other  side  it  draws  the  lip  directly  down  and  slightly 

1  Mecanisme  de  la  physioenomie  humaine  ou  analyse  electro-physiologique  de  I'expression  des 
passions.     Paris,  1876. 


250  THE  HUMAN  DENTAL  MECHANISM. 

everts  it.  It  is  used  in  the  expression  of  irony.  The  levator  hil)ii  in- 
ferioris  acts  with  its  fellow  in  raising  the  lower  li]).  It  protrudes  the 
chin,  as  in  pouting,  and  ])ro(hiees  dini])les  in  the  skin  of  the  chin. 
It  is  used  in  the  expression  of  doubt  and  disdain,  especially  when  aided 
by  the  triangularis  menti.  The  risorius  or  muscle  of  Santorini  is  ordi- 
narily spoken  of  as  the  smiling  muscle.  It  draws  the  corner  of  the 
mouth  directly  backward  and  produces  what  is  known  as  the  "sar- 
donic grin."  The  platysma  myoides  muscle  must  be  mentioned  in 
this  group  because  a  few  of  its  fibres  really  constitute  the  risorius 
muscle.  It  is  attached  above  mainly  to  the  subcutaneous  periosteum 
of  the  lower  jaw  from  the  symphysis  backward.  Its  middle  and 
anterior  parts  assist  in  depressing  tlie  jaw,  while  its  posterior  or  lower 
parts  are  largely  attached  to  the  corner  of  the  mouth,  and  act  to  draw 
the  lower  lip  and  angle  of  the  mouth  downward  and  backward,  and 
this  assists  in  the  expression  of  grief  and  fear. 

It  will  be  noted  that  the  buccal  orifice  and  its  surroundings  are  molded 
to  the  teeth  and  alveolar  process  by  the  tonicity  of  the  facial  portion 
of  the  orbicularis  and  the  muscles  which  connect  with  it.  The  loss  of 
the  teeth  and  the  subsequent  resorption  of  the  process  are  followed  by  a 
falling  in  of  these  tissues.  Inasmuch  as  they  are  no  longer  supported 
upon  a  solid  basis,  their  movement  is  restricted  in  amount  and  in  direc- 
tion. The  muscles  which  serve  to  carry  the  lips  upward  or  downward 
are  not  so  much  hampered  in  their  action  as  those  which  draw  the  lips 
and  the  mouth  backward.  This  limitation  is  more  particularly  due  to 
the  absence  of  the  canine  tooth  and  its  eminence  than  to  anything  else. 
All  expressive  movements  of  the  face  in  which  part  is  taken  by  the  oral 
muscles  are  limited  after  the  teeth  have  been  lost. 

In  a  succeeding  chapter  the  restoration  of  the  various  functions  of 
the  face  and  mouth  by  artificial  dentures  will  be  discussed.  It  is 
desirable  that  the  student  should  be  familiar  with  the  effect  of  the 
contraction  of  each  of  the  muscles  of  expression, in  orderthat  he  may  not 
impartto  the  countenance  any  unnatural  look  caused  by  too  great  fulness 
of  the  plate  at  anypoint.  A  denture  which  produces  the  same  effect  upon 
the  countenance  which  the  contraction  of  any  muscle  or  muscles  causes 
will  impart  to  that  countenance  the  expression  associated  with  th.e 
contraction  of  the  muscles  so  distorted.  This  will  be  discussed  more 
in  detail  in  Chapter  XII. 

FACIAL  EXPRESSION. 

The  human  countenance  is  made  up  of  the  features  of  the  face. 
Facial  expression  may  be  regarded  as  consisting;  first, of  the  features 
of  the  face,  which  are  considered  from  a  purely  anatomical  standpoint, 
and  are  the  result  of  natural  endowment;  and  second,  of  a  certain  impress 
made  upon  these  features  by  the  thoughts  and  actions  of  the  individual. 
The  natural  endowment  of  the  face  is  the  resultof  hereditaryinfluences, 
principally  those  of  race  and  parentage.  As  the  individual  grows  and 
develops  after  birth,  the  impress  of  thought,  of  action  and  of  experience 
IS  made  upon   the   countenance.     The    frequent    use    of    certain    of 


FACIAL  EXPRESSION.  251 

the  muscles  of  expression,  attendant  upon  the  existence  of  some 
thought  or  emotion,  cultivates  a  tonicity  of  those  muscles,  and  develops, 
folds  in  the  integument  of  the  face,  which  impart  a  certain  cast  or  ex- 
pression to  the  countenance.  These  two  influences  taken  together, 
the  one  prenatal  and  determining  the  anatomical  form  of  the  features 
the  other  postnatal  and  influencing  the  expression — establish  the  char- 
acter and  indentity  of  a  face.  In  discussing  the  human  countenance 
Mantegazza  gives  five  verdicts  which  may  be  taken  upon  it;  physiolog- 
ical, ethnological,  aesthetic,  moral  and  intellectual.  The  ethnological 
and  aesthetic  are  based  solely  upon  anatomical  characteristics,  while 
the  physiological,  moral  and  intellectual  are  more  largely  founded  upon 
expression.  The  term  facial  expression  in  its  broadest  sense  is  intended 
to  include  all  the  data  upon  which  these  several  judgments  are  based. 
In  this  chapter  it  will  be  used  with  that  meaning. 

Facial  expression  is  altered  by  the  loss  of  the  teeth  and  alveolar 
process  in  several  ways : 

First,  Absence  of  the  Teeth. — -The  teeth  are  displayed  in  the  move- 
ments of  the  lip  in  laughing,  in  smiling  and  in  speaking.  Cigrand^ 
says,  "Artists  tell  us  that  when  patients  speak  w^ords  as  "at"  or 
"ate"  with  the  short  or  long  sound  of  a,  the  lips  should  disclose  about 
one-half  of  the  labial  surface  of  the  anterior  teeth,  upper  and  lower, 
while  with  words  having  the  long  sound  of  o,  as  in  "oral"  or  "open" 
the  lips  should  hide  the  teeth  to  their  edges."  A  larger  proportion 
of  the  denture  is  displayed  in  smiling  or  in  laughter.  The  relation  of 
the  lips  and  the  anterior  teeth  during  these  acts  constitutes  one  of 
their  chief  elements  of  beauty,  and  it  is  during  their  performance 
that  a  beautiful  or  unsightly  denture  imparts  beauty  or  the  reverse 
to  the  countenance. 

Second,  Changes  of  Contour. — The  alteration  of  the  contour  of  the 
mouth  and  lips  by  the  loss  of  the  teeth  is  characteristic.  While 
it  is  less  marked  in  those  of  the  lymphatic  temperament  whose  short 
teeth  and  process  underlie  lips  which  are  thick  and  sufficiently  rigid 
to  undergo  little  change  after  the  teeth  are  lost,  yet  in  the  nervous 
temperament  where  the  lips  are  thin  and  require  support  from  the  teeth, 
the  alteration  in  appearance  is  striking.  The  changes  consist  of 
alterations  in  the  contours  of  the  lips  and  in  their  relations.  The  lips 
fall  inward  instead  of  incfining  outward  as  they  do  when  supported  by 
the  teeth.  The  proportion  of  mucous  membrane  which  is  displayed 
is  diminished.  The  line  of  separation  between  the  lips,  which  may  be 
an  element  of  great  beauty  in  a  mouth  becomes  changed,  being  altered 
in  most  instances  from  a  graceful  curve  to  a  characterless  straight 
line.  The  corners  of  the  mouth,  which  are  supported  mainly  by  the 
canines,  droop,  and  an  expression  of  weakness  is  imparted  to  the  face. 
There  is  a  disappearance  of  the  sulcus mento-labialis,  which  is  formed  at 
the  highest  point  of  attachment  of  the  soft  tissues  of  the  chin,  when  the 

1  Facial  Guide  Lines  as  Taught  by  Artists  and  Sculptors.  Paper  read  before  the  Fourth 
International  Dental  Congress,  1904. 


252 


THE  HUMAN  DENTAL   MECHANISM. 


lower  lip    is    supported  and  slightly  everted  by  the  teeth     (Figs.  22o 
and  227). 

Third,  Changes  in  the  Surface. — The  changes  which  occur  in  the  sur- 
face are  the  obliteration  of  some  of  the  normal  folds  in  the  skin  and 
the  establishment  of  additional  ones.  Before  discussing,  however, 
those  which  result  from  the  loss  of  the  teeth,  it  will  be  necessary  to 
point  out  those  which  result  from  old  age,  in  order  that  no  confusion 
between  the  two  shall  arise.  The  changes  which  ensue  in  old  age  are 
the  result  of  two  conditions:  the  absorption  of  the  fat  contained  in  the 
substance  of  the  lips  and  cheeks,  and  the  atrophic  changes  which  occur 
in  the  skin.  These  result  in  the  obliteration  of  contours  at  points  sup- 
ported by  cushions  of  fat  and  in  the  establishment  of  wrinkles  in  the 


Fig.  224 


Photograph  slinwiriK  the  wrinkles  commonly  observed  in  old  age. 

skin  at  points  in  the  line  of  frequent  muscular  action.  Normally  there 
are  masses  of  fat  located  in  the  hollow  of  the  cheek  around  the  buc- 
cinator and  zygomatic  muscles.  There  is  usually  also  some  beneath  the 
levator  labii  superioris  muscle  and  some  at  the  .symphysis  of  the  lower 
jaw.  These  may  be  absorbed  early  in  life  because  of  defective  nutri- 
tion. They  are  frequently  absorbed  after  middle  life  in  certain  tem- 
peraments, notably  the  nervous.  In  the  sanguine  or  lymphatic  they 
are  more  likely  to  persist  through  old  age. 

In  most  individuals  past  forty,  wrinkles  of  the  skin  are  apt  to  be 
established,  although  as  is  true  in  the  case  of  the  absorption  of  the  fat, 
they  are  likely  to  appear  earlier  in  a  nervous  face  than  in  that  of  other 
temperaments.  Camper  has  called  attention  to  the  fact  that  they  are 
established  at  right  angles  to  the  line  of  muscular  action.  Tho.se 
normally  seen  in  an  individual  after  forty  are  the  transverse  wrinkles 
of  the  forehead,  vertical  wrinkles  of  the  forehead,  crow's  feet  or  wrinkles 
at  the  external  canthus  of  the  eye,  the  naso-labial  fold,  which  extends 


FACIAL  EXPRESSION. 


253 


downward  and  outward  into  the  check  from  the  base  of  the  ala  of  the 
nose,  and  the  genio-mental  wrinkles,  extending  from  the  cheeks  to 
the  chin  (Fig.  224). 


Fig.  225 

^g| 

^^^^^^^iJr 

w 

IHHi 

^ 

^E|^^ 

^^^^^^^■j^^j^^g^l 

L 

Photograph  showing  effect  of  the  loss  of  the 
teeth  upon  the  mouth,  and  the  wrinkles 
established  thereby. 

Fig.  227 


Photograph  showing  the  effects  of  the  loss 
of  the  teeth  upon  the  profile. 


Fig.    228 


Photograph  showing  effect  of  the  loss  of 
tne  teeth.    Front  view  of  patient  in  Fig.  228. 


Photograph  showing  the  effect  of  the  loss 
of  the  teeth  upon  the  profile. 


The  loss  of  the  teeth  is  followed  by  additional  changes  in  the  coun- 
tenance. The  naso-labial  fold  is  accentuated  because  the  upper  lip 
falls  in,  and  frequently  becomes  two  lines,  one  of  which  descends  from 


254  THE  IIUMAS  DENTAL  MECHANISM. 

the  ala  of  the  nose  to  the  corner  of  the  mouth  (Fif^;.  225).  The  phihrum 
is  usually  obhterated  (Fig.  227).  This  is  due  principally  to  the  increase 
of  the  sphincter  action  of  the  orbicularis,  which  becomes  necessary  to 
keep  the  mouth  closed  in  order  to  confine  the  saliva  and  food.  Usually 
a  groove  is  established  extending  from  the  corner  of  the  mouth  in  the 
direction  of  the  chin.  In  addition  to  these,  small  wrinkles  placed  radially 
to  the  oral  orifice  are  established.  While  these  last  normally  exist  in 
old  people,  they  are  much  accentuated  when  teeth  are  lost  because 
of  the  marked  sphincter  action  of  the  orbicularis  above  alluded  to. 

Fourth,  Changes  in  the  Relation  ot  the  Jaws. — The  removal  of  the 
points  of  contact  between  the  jaws  results  in  their  approximation. 
This  is  attended  by  a  shortening  of  the  soft  tissues  extending  between 
the  two;  the  muscles  and  connective  tissues  being  actually  decreased 
in  lent'th.  As  far  as  the  lines  of  the  face  are  concerned, this  effect  is 
particularly  noticed  in  the  decreased  distance  between  the  nose  and 
the  chin.  In  some  instances  this  effect  is  marked,  the  nose  and  the 
chin  coming  so  close  together,  that  a  characteristic  deformity  is  noticed. 

Fifth,  Alteration  of  the  Profile. — This  is  always  changed  to  a  greater 
or  less  extent.  In  those  cases  in  which  only  a  small  amount  of  absorp- 
tion of  the  alveolar  process  has  occurred,  there  is  only  a  flattening  of 
the  mouth  (Fig.  228),  while  in  others  the  falling  in  of  the  lips  may  be 
very  marked  (Fig.  226). 

Sixth,  Alteration  of  Expression. — From  what  has  been  said  con- 
cerning facial  expression,  or  that  which  gives  character  and  identity  to 
the  countenance,  it  must  be  seen  that  a  condition  which  is  succeeded  by  so 
pronounced  a  change  in  the  features  must  greatly  alter  the  charac- 
teristic expression  of  a  face.  One  has  but  to  remember  the  striking 
change  in  appearance  which  has  succeeded  the  extraction  of  all  of  the 
teeth  of  an  acquaintance  to  appreciate  how  marked  an  effect  it  has 
upon  this  means  of  identification. 


CHAPTER   V. 

THE  HUIMAN  DENTAL  MECHANISM  AS  MODIFIED  BY  TEMPERA^IENT, 

AGE,  AND  USE. 

By  a.  H.  Thompson,  D.D.S.,  and  CmiRLES  R.  Turner,  D.D.S.,  M.D. 

The  functional  relations  of  the  human  denture  having  been  discussed 
in  the  preceding  chapter,  it  is  proposed  in  this  to  treat  of  those  consider- 
ations relative  to  its  appearance  which  are  important  from  the  stand- 
point of  dental  prosthesis.  xAji-tificial  dentures  are  recjuired  not  only  to 
restore  the  functions  of  the  natural  organs  which  they  substitute,  but 
they  must  also  restore  as  far  as  possible  the  former  appearance  of  the 
mouth  and  face. 

In  nature  there  is  a  certain  harmony  in  the  various  physical  charac- 
teristics of  each  individual.  There  is,  for  instance,  a  pleasing  proportion 
in  the  various  parts  of  the  body,  and  while  this  proportion  varies  some- 
what among  indi\iduals,  as  they  are  not  all  constructed  upon  the  same 
physical  plan,  normally  these  variations  occur  within  fairly  well-defined 
limits,  and  a  marked  departure  from  the  plan  is  at  once  recognizable 
as  abnormal.  The  size  and  shape  of  the  teeth  bear  in  general  a  certain 
ratio  to  the  size  and  shape  of  the  body,  or  more  especially  to  the  size  and 
shape  of  the  head  or  face,  but  this  is  by  no  means  fixed  and  varies  some- 
what within  the  limits  of  the  normal.  The  mensural  proportions  of  the 
teeth  of  different  individuals  differ  vastly,  but  for  the  most  part  they  cor- 
respond to  the  bodily  dimensions  of  the  individuals  owning  them.  This 
is  also  true  of  their  surface  form  and  contours,  which  similarly  correspond 
to  these  characteristics  of  the  physique  of  their  owners.  There  is  also  a 
general  relation  between  the  color  of  the  teeth  and  that  of  the  other  pig- 
mented tissues  of  the  body. 

^^^lile  this  harmonious  correspondence  between  the  physical  character- 
istics of  the  teeth  and  those  of  the  body  is  not  absolutely  universal,  it  is 
the  general  rule,  and  any  departure  from  it  marks  the  individual  as  un- 
usual. This  bodily  harmony  is  taken  as  the  basis  for  the  selection  of 
teeth  in  dental  prosthesis.  Familiarity,  therefore,  with  the  physical  char- 
acteristics of  the  teeth  and  of  the  body  and  their  mutual  association  is 
necessary  to  a  judicious  selection  of  artificial  teeth  to  replace  the  natural 
ones.  With  a  view  to  acquainting  the  student  wdth  this,  the  dental  ap- 
paratus in  its  relation  to  the  general  physique  and  the  characteristics 
of  each  will  be  discussed  in  this  chapter.  The  denture  will  be  described 
from  the  standpoint  of  its  natural  endowment  first;  that  is  to  say,  its 
variations  in  the  various  temperamental  t\-pes  of  mankind.  Secondly, 
the  changes  which  occur  in  it  under  the  influence  of  age  and  use  will  be 
described. 

255 


256  THE  HUMAN  DENTAL  MECHANISM. 

TEMPERAMENT. 

Temperament  according  to  Flagg  is  a  term  used  to  express  differ- 
ences in  the  mental  and  physical  constitution  of  individuals.  It  has 
been  used  with  this  designation  since  the  days  of  Hippocrates,  the  ear- 
liest systematic  writer  upon  the  subject.  It  is  an  attempt  at  the  classi- 
fication of  mankind  according  to  his  physical  characteristics,  and  has 
as  its  basis  the  relative  proportion  of  his  mechanical,  nutritive  and 
nervous  systems,  and  the  relative  energy  of  the  various  functions  of 
the  body.  "Each  temperament  is  the  result  as  well  as  the  indication 
of  the  preponderence  of  one  or  another  of  these  systems  and  of  their 
relative  functional  activity." 

Despite  the  antiquity  of  this  classification  it  is  commonly  utilized  in 
dental  prosthesis  at  the  present  time  for  lack  of  a  better.  Descriptive 
anthropology  and  ethnology  have  not  as  yet  presented  a  classification 
of  the  physical  attributes  of  man  which  is  a  satisfactory  substitute  for 
that  according  to  temperament.  Ethnic  peculiarities  are  sufficiently 
fixed  to  identify  individuals  whose  racial  characteristics  are  not  mixed, 
but  pure  races  exist  in  so  few  quarters  of  the  globe  that  this  basis  of 
classification  is  valueless  and  a  more  fundamental  one  is  necessarv. 

In  its  ordinary  use  temperament  refers  equally  to  mental  and  physi- 
cal attributes.  It  does  not  divide  mankind  into  well-marked  natural 
groups  which  may  be  distinguished  anatomically,  but  it  offers  groups  of 
associated  physical  characteristics,  the  possession  of  a  majority  of 
which  by  an  individual  assigns  him  to  that  group.  When  the  pre- 
dominating temperament  of  an  individual  has  been  determined  ac- 
cording to  this  plan  as  a  preliminary  to  the  restoration  of  lost  parts 
Hke  the  teeth,  the  result  will  be  harmonious  if  these  are  selected  to  ac- 
cord with  the  physical  characteristics  of  that  temperament. 

According  to  the  present  generally  accepted  classification  there  are 
four  fundamental  divisions  of  the  temperaments.  The  bilious,  in 
which  there  is  marked  activity  in  the  function  of  the  liver;  the  san- 
guine, in  which  the  circulatory  system  is  most  prominent;  the  nervous, 
characterized  by  a  highly  developed  central  nervous  system;  and  the 
lymphatic,  in  which  the  lymphatic  system  has  a  preponderating  influence. 

The  following  is  a  description  of  the  general  mental  and  physical 
characteristics  of  the  basal  temperaments,  and  while  these  are  to  be 
considered  chiefly  from  the  physical  standpoint,  the  mental  attributes 
are  appended  for  assistance  in  diagnosis. 

The  Bilious  Temperament.  (Fig  229.) — Physical  characicristics:  the 
pulse  is  hard  and  strong;  frame  muscular;  movements  without 
grace;angularity  of  features  and  physique;  stature  is  medium  or  tall; 
body  has  a  firm  pose;  countenance  is  severe  and  serious;  complexion 
ordinarily  sallow  or  swarthy;  the  hair  dark  brown  or  black;  eyes  black 
or  brown.  Mental  characteristics:  strong  susceptibility  and  constancy 
of  feeling;  quick  perception  and  precise  judgment;  capacity  for  reason- 
ing; firm  decision  and  will  power;  great  violence  in  anger;  stubbor- 
ness;  great  pride  and  ambition;  usually  generous  and  magnanimous. 


TEMPERAMENT. 


257 


Fig.  229 


Fig.  230 


Man  with  characteristics  of  the    biliou'i    tem- 
perament in  preilominenee. 


Fig.  231 


Individual  with  characteristics    of    the    san- 
gnine  tonip;^rame:it  in  prodaminence 


Fig.  232 


Individual    with   characteristics  of    the    ner- 
vous temperament  in  predonainence. 


Individual  with    characteristics  of  the  lym- 
phatic   temperament  in  predominence. 


The  Sanguine  Temperament.  (Fio-.  230.) — PJiysical  cJiaracteristics: 
the  highest  manifestation  of  physical  life;  active  circulatory  system; 
pulse  excitable  and  irregular;  stature  above  the  medium;  body  well 
proportioned;  movements  graceful,  regular  and  easy;  athletic  type; 
voluptuousness  in  females;  vivacious  and  beautiful;  complexion  fresh 
and  ruddy;  red  lips;  hair  light  or  auburn,  rarely  dark,  sometimes  red; 
eyes  are  light  in  color,  usually  blue.     Mental  characteristics:      Great 


258  THE  II (MAX   DENTAL    MlX'IIAMSAf. 

liopefulness  and  elasticity  of  iiiind,  ()])tiinisin;  enthusiastic,  hut  have 
litde  perseverance;  fondness  for  achniration  or  display;  fickleness; 
great  liberality  of  sentiment;  little  al)ility  for  self-denial;  seldom  undergo 
mental  sullering. 

Nervous  Temperament.  (Fig.  231.) — Physical  cluirddcrtstics:  Quick 
movements;  great  sensitiveness;  muscular  system  small;  body  refined 
and  slender;  angular;  head  proportionately  large;  the  skin  is  soft  and 
of  fine  texture;  complexion  generally  light,  sometimes  sallow;  hair  is  fine 
and  dark;  not  plentiful;  eyes  gray  or  very  dark.  Mental  charactcrisfics: 
very  highly  organized;  great  fluctuation  of  feeling  of  exhaltation  or 
depression;  keen  sympathy;  great  anxiety  or  fear;  ability  to  endure 
physical  suffering  in  excess  of  what  would  be  expected;  predominates 
in  highly  civilized  countries. 

The  Lymphatic  Temperament.  (Fig.  232,) — Physical  characteris- 
tics: tends  to  heaviness  and  roundness  of  the  body;  medium  or  low 
stature;  cellular  repletion  due  to  lymph;  slow  circulation;  pulse  weak; 
large  rounded  head;  features  heavy  and  expressionless;  hair  light  and 
coarse  without  lustre;  complexion  heavy  and  muddy;  eyes  dull  gray 
and  small.  Mental  cl i ar a -t eristics:  Little  passion  or  ambition,  great 
self  satisfaction;  contentment  and  good  nature  marked;  judgment 
calm,  and  slow  but  sure;  plodding  and  industrious;  individuals  success- 
ful in  business;  safe  to  trust. 

The  physical  characteristics  associated  with  the  four  basal  tempera- 
ments are  well  described  and  may  be  easily  studied  in  the  comparative 
table  on  page  259  prepared  by  Dr.  A.  H.  Thompson.  It  must 
be  remembered  that  these  are  basal  temperamental  types  which  are 
more  ideal  than  real,  and  that  pure  types  seldom  occur.  Few  indi- 
viduals exist  who  possess  all  the  characteristics  of  a  single  tempera- 
ment. 

The  description  applies  therefore  more  largely  to  principles  than 
to  individuals,  but  the  tables  of  binary  temperamental  compounds 
on  pages  260  and  201  describe  combinations  of  physical  characteris- 
tics which  may  frequently  be  ob.served  in  individuals.  Combinations 
of  three  basal  types  exist  in  many  persons,  ■  and  in  addition 
there  is  a  large  class  in  whom  the  temperamental  indication  is  so 
obscure  as  not  to  be  discernible  at  all.  In  the  diagnosis  of  the  temper- 
aments or  the  predominating  temperamental  indication  in  any  in- 
dividual, constant  observation  of  people  and  keen  perception  are 
necessary  and  good  judgement  in  selecting  the  characteristics  which 
are  most  significant.  No  rule  can  be  given  which  will  completely  cover 
the  ground,  but  the  proportion  of  individuals  who  do  not  possess  char- 
acteristics which  indicate  the  predominance  of  one  temperament 
over  the  others,  is  small.  In  America  because  of  the  larger  number  of 
races  which  have  contibuted  to  its  population,  the  diagnosis  of  temper- 
ament is  particularly  difficult.  The  sanguine  and  bilious  are  the 
usual  basal  temperaments  in  this  country  although  these  are  not  so 
distinctive  as  is  the  nervous  of  the  Latin  races  and  the  lymphatic  of  the 
German  and  Dutch  races. 


TEMPERAMENT. 


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TIIE  JICMAX    DESTAL    MK('UAMS.}f. 


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TEMPERAMENT.  263 

TIk'  illustrations,  Figs.  233,  234,  235,  and  230,  show  characteristic 
dentures  of  tlie  four  basal  temperaments. 

Fig.  233 


Denture  whose  characteristics  are  chiefly  those  of  the  bilious  temperament.     (Photograph  of 
a  specimen  in  the  Wistar  Institute  of  Antomy.) 

Fig.  234 


Dentuj'e  whose  characteristics  are   chiefly  those  of  the  nervous  temperament.       (Photograph 
of  skull  in  collection  of  Dr.  V.  Walter  Gilbert.  1) 

Fig.  235 


Denture  whose  characteristics  are  chiefly  those  of  the  sanguine  temperament.     (Photograph  of 
a  specimen  in  the  Wistar  Institute  of  Anatomy.) 


264 


Till-:   lll'MAX    DKSTM.    MKcllAMs.V. 


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2(JG  THE  HUMAN   DENTAL  MECHANISM. 


Denture  whose  characteristics    are  chiefly  those  of  the  lymphatic  toiiipfrarneril.  (Cryer.) 

AGE. 

From  infancy  to  old  age  a  gradual  succession  of  changes  in  the 
bodily  tissues  occurs.  In  common  with  the  other  tissues  of  the  body, 
the  teeth  are  influenced  by  the  increasing  years.  From  the  time  of 
the  establishment  of  the  permanent  denture  until  the  time  it  is  lost, 
these  changes  occur  in  regular  progression,  so  that  for  the  most  part 
the  physical  characteristics  of  the  teeth  are  constantly  in  accord  with 
the  physical  characteristics  of  the  individual  at  all  times  during  his 
life.  In  some  persons  these  alterations  are  more  discernible  than  in 
others,  but  after  the  age  of  thirty-five  or  forty  the  marks  of  time  may  be 
found  in  almost  every  instance. 

The  chief  alteration  which  may  be  attributed  to  the  influence  of  age 
is  a  deepening  of  the  color  of  the  teeth.  This  is  a  molecular  change  in 
their  tissues  which  is  physiolgic  in  nature.  It  occurs  most  strikingly 
in  individuals  of  the  bilious  and  saguine  temperaments,  the  yellow  shades 
of  whose  teeth  are  markedly  deepened.  This  change  amounts  to  two 
or  three  shades  as  measured  by  the  shade-guide  for  artificial  teeth. 
It  also  occurs  to  a  lesser  degree  in  the  teeth  of  the  nervous  and  lymphatic 
temperaments.  Due  regard,  therefore,  should  be  taken  of  this  fact  in 
the  selection  of  artificial  teeth  for  individuals  past  forty, and  a  propor- 
tionally darker  shade  of  the  color  suitable  for  each  temperament  should 
be  selected  to  correspond  with  the  age. 

Beside  the  wear  of  the  teeth,  which  is  to  be  discussed  later  and  which 
is  a  frequent  accompaniment  and  an  indirect  result  of  old  age,  another 
influence  of  age  must  be  mentioned.  This  is  the  physiologic  recession 
of  the  gums  about  the  crowns  of  the  teeth  which  occurs  as  life  goes  on. 
It  must  not,  of  course,  be  confounded  with  recession  of  the  gums 
due  to  pathological  processes.  In  individuals  past  forty  there  is  a 
recession  of  the  gum  tissue  from  about  the  necks  of  the  teeth,  exposing 
the  cementum.  The  round  full  festoons  of  the  gingiva^  characteristic 
of  youth  disappear,  and  instead,  the  line  between  the  gum  and  the  teeth 
becomes  accentuated.     This  is  more  strikingly  evident  in  some  tem- 


THE  USE  OF  THE  TEETH.  2(57 

peraments  than  in  others.  It  occurs  particularly  in  individuals  of  the 
lyiupiuiticjsanguincundhilio-lymphatic  temperaments.  In  the  arrange- 
ment of  the  gums  of  artificial  dentures  due  cognizance  should  be  taken 
of  this  peculiarity. 

THE  USE  OF  THE  TEETH. 

The  use  of  a  denture  through  the  course  of  a  human  life  must  neces- 
sarily leave  some  evidences  of  v^ear  upon  the  teeth.  Although  the 
enamel  covering  the  teeth  is  the  hardest  structure  in  the  body, yet  it  is 
unable  to  resist  the  wear  which  occurs  in  the  performance  of  the 
masticatory  function.  T  he  character  and  the  amount  of  wear  of  the  teeth 
depends  upon  three  factors:  the  food,  the  manner  of  movement  of  the 
jaw,  and  the  character  of  the  dental  tissues  themselves.  According  to 
J.  H.  WassaP  and  A.  H.  Thompson"  the  teeth  in  the  skulls  of  pre- 
historic man  show  evidences  of  great  wear.  They  wore  out  in  the 
performance  of  their  daily  duties,  because  of  the  rough  character  of 
the  food.  For  the  same  reason  skulls  of  American  Indians  display 
similar  evidences  of  attrition,  large  quantities  of  finely  divided  sand 
having  become  mixed  with  their  corn  meal  in  its  manufacture. 
Modern  conditions  of  civilization  are  not  so  conducive  to  wear  of 
the  teeth.  Individuals  are  frequently  seen  who  have  reached  the  age 
of  thirty-five  or  forty  years  and  yet  exhibit  little  evidences  of  wear. 

The  amount  of  wear  bears  no  relation  to  the  age  of  the  individual. 
It  is  more  directly  related  to  the  temperament,  or  in  other  words,  to 
the  physical  resistance  of  the  teeth  in  certain  temperaments.  Wear 
occurs  most  commonly  in  those  of  the  lymphatic  temperament,  and  in 
the  combinations  of  this  temperament  and  the  bilious  with  the  san- 
guine. 

Harrison  Allen  says,  "the  wear  is  not  related  to  the  form  of  the 
condyle  of  the  jaw,"  but  inasmuch  as  worn  conditions  of  the  teeth  are 
most  frequently  found  in  cases  characterized  by  lateral  movement  of  the 
jaw%  it  is  believed  that  they  must  be  connected  in  some  w-ay. 

The  existence  of  certain  habits,  as  that  of  tobacco  chewing,  as  pointed 
out  by  A.  H.  Thompson^  is  responsible  for  wear  of  the  teeth,  the  silica 
mixed  with  the  tobacco  exerts  an  abrasive  influence  upon  the  teeth. 
According  to  I.  B.  Davenport*,  in  a  perfect  denture  wear  proceeds 
evenly  upon  all  its  morsal  surfaces.  Thompson  describes  the  pro- 
cess as  follov/s:  "The  points  of  the  tubercles  of  the  molars  and  the 
cusps  of  the  bicuspids  and  canines  are  first  worn  off,  exposing  the  den- 
tine, which  wears  out  in  little  cups  surrounded  by  a  wall  of  enamel. 
The  edges  of  the  incisors  are  worn  to  show  a  fine  line  of  dentine."  In 
those  temperaments  in  which  the  cusps  are  short,  as  the  wear  proceeds 
further,  the  lower  jaw  moves  forw^ard,  so  that  the  incisors  are  brought 
into  the  position  of  an  edge-to-edge  bite.  Dentures  wnth  long  pene- 
trating cusps  exhibit  a  different  kind  of  wear  from  those  in  which  the 

1   The  Dental  Cosmos.Vol.  xliii.,  p.,  977.  *   The  Dental  Cosmos.  Vol.  xlii.,  p.  519. 

"  The  Dental  Cosmos,  loc.  cit.  *    International  Dental  Journal. 


268 


THE  ITlUrAN   DEXTAL    MECHANISM. 


cusps  are  short.  The  following  degrees  are  noted  by  C.  H.  Ward"; 
1st  degree,  enamel  somewhat  worn;  2d  degree,  cusps  disa})jiear 
and  dentine  exposed;  3d  degree,  teeth  reduced  in  height;  4th  degree, 
teeth  worn  off  to   the   necks. 

It  is  evident  from  the  standpoint  of  dental  j)rosthesi.s  that  the  imita- 
tion of  extreme  degrees  of  wear  is  undesirable.     It  will  seldom  be 


Fig.  237 


Fig.  238 


'ryp'cal  arch  outline  of  bilious  temperament. 
(Fhotograpti  of  a  specimen  in  the  Wistar  In- 
•stitute  of  Anatomy.) 


Typical  arch  outline  of  nervous  temper.i- 
ment.  (Photograph  of  a  specimen  in  the  col- 
lection of  Dr.  M.  H.  Cryor.) 


Fig.  239 


Typical  arch  outline  of  sanguine  temper- 
ament. (Photograph  of  a  specimen  in  the 
collection  of  Dr.  M.  H.  Cryer.) 


Typical  arch  outliiieof  lymphatic  tempera- 
ment. (Photograph  of  a  specimen  in  the  Wis- 
tar Institute  of  Anatomy.) 


found  wise  to  imitate  more  than  the  first  and  second  degrees,  inas- 
much as  the  third  and  fourth  are  seldom  seen  excepting  among  savage 
people.  Of  the  first  degree  two  t\^es  of  wear  are  noted  as  worthy  of 
imitation  so  far  as  the  incisors  are  concerned.  They  are,  first,  that 
observed  in  cases  in  which  there  is  a  pronounced  overbite.  (Fig. 
197.)      In  this  in  the  forward  and  backward  movement  of  the  jaw, 

'  The  Dental  Cosmos,  Vol.  xl.  p.  261. 


THE  USE  OF  THE  TEETH. 


269 


tlie  occlusal  ends  of  the  upper  and  lower  incisors  are  worn,  the  wear 
upon  the  up{)er  occurring-  at  the  expense  of  the  lingual  surface,  that 
upon  the  lower  beini;  at  the  expense  of  the  labial.  This  results  in  a 
straightening  of  the  line  of  occlusal  edges  of  the  incisors  in  both  jaws. 


Fig.  241 


Denture  exhibiting  first  degree  of  wear.     (Photographed  from  living  subject) 

Fig,  242 


Denture  exhibiting  second  degree  of  wear.       (Photograph  of  skull  in  collection  of  Department 
of  Dentistry,   University  of  Pennsylvania.) 


Fig.  243 


.i  '^^^!^^  '--'^'^      ■     a '■■^*^^-^  ^- 


TUhi 


Denture  exhibiting  second  degree  of  wear  on  the  right,  third  degree  on  the  left.     (Photographs 
of  skulls  in  collection  of  Department  of  Dentistry,  University  of  Pennsylvania.) 

the  labial  surfaces  of  the  upper  and  the  lingual  of  the  lower  ending 
in  a  sharp  edge  which  is  more  or  less  continuous  from  side  to  side. 
(Fig.  24L)  After  a  while  some  little  chipping  of  the  enamel  edge  of 
the  upper  may  occur  making  this  line  irregular.  The  second  type  oi 
wear  in  the  incisor  region  is  that  in  which  the  overbite  is  not  so  pro- 


270  ^^^^'  I^UMAX  DEXTAL  MECHANISM. 

nounced,  where  the  incisal  edges  of  the  lower  teeth  move  more  nearly 
directly  across  the  edges  of  the  upper.  This  results  in  the  wearing  of 
grooves  at  such  places  as  the  teeth  come  in  contact.  (Fig.  242.)  This 
is  not  so  extensive  a  degree  of  wear  as  occurs  in  the  first  type,  and  is 
more  frequently  observed. 

The  second  degree  of  wear  in  the  incisal  region  is  common  to  those 
dentures  in  which  an  edge-to-edge  bite  exists.  Here  the  enamel  is  ex- 
tensively worn  through  and  the  dentine  is  exposed.  ^Fig.  243.)  As 
the  attrition  proceeds  the  length  of  the  crown  is  gradually  reduced,-  the 
dentine  is  frequently  stained  and  a  characteristic  appearance  results. 
The  margins  of  the  enamel  are  chipped  and  an  irregular  incisal  line  is 
produced. 


CHAPTER    VI. 

THE   EXAMINATION,  PREPARATION,  AND   STUDY   OF  THE   MOUTH 
PRELIMINARY  TO  THE  INSERTION  OF  ARTIFICIAL  TEETH. 

By  a.  DeWitt  Gritman,  D.  D.  S. 

A  CAREFUL  preliminary  examination  of  the  mouth  is  a  matter  of  \'ital 
importance  to  the  successful  insertion  of  substitutes  for  the  natural 
teeth.  Two  objects  are  held  in  view  in  this  examination:  The  first 
is  to  determine  the  state  of  health  of  the  tissues  of  the  mouth,  particu- 
larly of  those  to  be  in  relation  with  the  artificial  denture.  As  the  latter  is 
at  best  a  foreign  body,  and  does  not  tend  to  improve  the  general  hygiene 
of  the  mouth  cavity,  it  is  important  that  the  tissues  with  which  it 
comes  in  contact  shall  be  perfectly  healthy  and  not  the  seat  of  patho- 
logical processes.  It  is  also  an  evident  necessity  that  the  tissues  which 
are  to  afford  support  to  the  denture,  whether  it  be  plate  or  bridge,  must 
be  sound  and  strong.  In  this  connection  must  also  be  considered 
the  means  of  bringing  these  tissues  to  a  state  of  health  and  usefulness 
in  cases  where  the  latter  condition  does  not  exist. 

The  second  object  has  to  do  with  plans  for  the  prospective  denture. 
At  this  examination  it  wdll  be  necessary  to  determine  the  type  of  denture 
which  is  to  be  employed,  the  general  plan  of  its  construction,  its  means 
of  retention,  and  whether  the  mouth  is  favorable  thereto,  together  with 
any  means  necessary  to  prepare  the  mouth  for  the  reception  of  the  den- 
ture. In  \dew  of  these  facts,  it  is  evident  that  thoroughness  in  this 
preliminary  examination  is  desirable. 

The  condition  of  the  soft  tissues  of  the  mouth  may  be  ascertained 
by  visual  examination,  either  directly  or  by  means  of  a  mouth  mirror 
and  by  palpation  wdth  the  finger. 

Familiarity  ^\ith  the  general  appearance  of  healthy  mucous  membrane, 
its  color  and  consistence,  and  ability  to  recognize  aberrations  from  this 
should  be  part  of  the  equipment  of  the  examiner.  If  the  mucous 
membrane,  which  in  the  normal  state  is  a  firm  resistant  structure 
capable  of  giving  adequate  support  to  the  denture,  is  not  in  a  state  of 
health,  it  is  evident  that  it  must  be  brought  to  this  condition  before  the 
impression  is  taken.     This  T\dll  presently  be  discussed. 

If  the  mouth  is  edentulous,  and  inspection  shows  its  tissues  to  be 
healthy,  further  examination  and  study  have  only  to  do  with  the  plans 
for  the  denture.  A  careful  digital  exploration  of  the  entire  surface  to 
be  covered  by  the  future  plate  should  be  made  to  determine  the  loca- 
tion of  hard  or  soft  areas,  as  account  must  be  taken  of  these  in  providing 
for  the  retention  of  the  plate.  Special  attention  must  be  paid  to  the 
retention  of  the  plate  in  the  lower  jaw,  and  as  this  \\ill  mainly  depend 
on  the  action  of  the  muscles  attached  to  the  mandible,  the  location 

•271 


272  THE  STUDY  OF   THE  MOUTH. 

of  the  margins  of  the  future  plate  must  be  carefully  noted,  as  well  as 
the  positions  of  the  labial  and  lingual  frsena.  These  should  be  accu- 
rately marked  ui)()n  the  cast,  for  if  these  be  neglected  in  all  probability 
the  lower  plate  will  not  rest  undisturbed  upon  the  jaw. 

If  there  are  teeth  in  the  mouth  the  examination  must  determine  if 
they  are  strong  and  healthy,  and  if  not,  whether  they  may  be  made  so. 
A  judgment  of  their  probable  tenure  of  life  and  usefulness  must  also  be 
formed  in  this  preliminary  survey.  The  presence  of  teeth  and  their 
location  must  be  accurately  mai)i)ed  and  recorded,  and  if  these  be  .scat- 
tered in  the  front  of  the  mouth  their  color  and  position  must  be  care- 
fully noted. 

MORBID  CONDITIONS  OF  THE  GUMS. 

The  condition  of  the  gums  in  the  mouths  of  many  patients  presenting 
themselves  for  prosthetic  work  is  not  always  favorable  to  the  immediate 
insertion  of  artificial  dentures.  It  is  inadvisable  to  ])lace  an  artificial 
denture  in  a  mouth  until  all  the  tissues,  especially  those  in  direct  relation 
with  the  plate,  are  in  a  healthy  condition. 

A  general  hypenemia  of  the  mucous  membrane  is  frequently  present, 
produced  by  the  presence  of  roots  or  fragments  thereof,  or  of  more  or 
less  diseased  teeth.  This  is  frequently  aggravated  by  a  general  lack  of 
hygienic  care  on  the  part  of  the  indi\  idual  l)ecause  of  a  hypersensitive 
condition  of  the  mucous  membrane  and  tenderness  of  the  remaining 
teeth.  The  removal  of  the  useless  roots  and  teeth,  and  the  use  of  an 
astringent  antiseptic  mouth-wash,  is  usually  all  that  is  necessary  to 
render  the  mouth  in  suitable  condition  to  receive  the  denture. 

Long-continued  sickness  is  frequently  responsible  for  gingival  inflam- 
mation, which  is  increased  generally  by  lack  of  proper  care  of  the  oral 
cavity  during  the  period  of  illness  and  even  during  convalescence.  It 
may  be  remarked  that  proper  care  of  the  oral  cavity  during  illness  is 
not  yet  one  of  the  sohed  problems  in  nursing. 

Stomatitis  is  not  infrefjuently  observed.  As  its  name  indicates  in  a 
general  way,  it  is  inflammation  of  the  mouth,  but  this  term  embraces  a 
large  number  of  subdiseases,  such  as  a])hthous  stomatitis,  ulcerative  sto- 
matitis, mercurial  stomatitis,  syphilitic  inflammations,  etc.,  divisions 
too  numerous  for  the  average  prosthetic  worker  to  treat  satisfactorily, 
and  they  had  best  be  referred  to  a  specialist  for  proper  treatment. 
Stomatitis  simplex,  or  ordinary  inflammation  of  the  mucous  membrane, 
is  so  common  that  it  should  come  under  his  sjx'cial  care.  If  this  exists, 
there  must  be  careful  hnage  of  the  mouth  three  or  four  times  a  day  with 
an  antiseptic  solution.  Potassium  chlorate,  15  grains  to  the  ounce  of 
water,  is  an  effective  mouth-wash.  A  2  per  cent,  solution  of  hydro- 
naphthol  in  alcohol  is  another  excellent  mouth-wash  for  all  forms  of 
gingival  inflammation.  If  this  condition  is  the  result  of  gastric  disturb- 
ance, much  help  may  be  gained  by  the  use  of  the  following  for  internal 
administration : 

H.     Acidi  hydrochlorici  dil fo'J- 

Sig. — Five  drops  well  diluted  with  water  after  ineala. 


EETEyTIOX  OE  EXTRACTION  OF  NATURAL   TEETH.         27.] 

iNIuc'h  of  the  gingivitis  found  contiguous  to  remaining  sound  teeth  is 
due  to  calcuh  at  the  free  margin  of  the  gums.  This  may  result  in  ex- 
tensive infiammation  of  the  peridental  membrane  and  finally  in  pyorrhea 
alveolaris.  A  discussion  of  the  treatment  of  the  latter  properly  belongs 
elsewhere.  Suffice  it  to  say  that  all  teeth  must  be  thoroughly  scaled, 
and  the  patient  advised  to  use  the  following  mouth-wash: 

B.     Zinci  chloridi 5-10  gr.; 

Aquse  menth.  pip 5'J- — -^I- 

Sig. — Use  as  a  mouth-wash  for  a  week. 

Another  formula  will  be  found  excellent: 

B.     Hydronaphthol gr.  xx; 

.\lcoholis oi : 

Aquae 5j. — M. 

Sig. — Twenty  drops  to  a  small  tumbler  of  water,  as  a  mouth- wash,  to  be  used  once  daily. 

Unless  teeth  so  affected  are  placed  in  a  healthy  condition,  it  is  useless 
to  attempt  to  insert  a  plate  while  they  remain  as  centers  of  disease. 

It  is  unnecessary  to  enlarge  further  in  this  direction,  as  it  would  carry 
this  chapter  too  far  afield  to  attempt  to  cover  all  the  pathological  condi- 
tions interfering  with  the  insertion  of  artificial  dentures.  Siiffice  it  to 
say  that  all  pathological  lesions  of  the  tissues  of  the  mouth  of  whatever 
natiu-e  must  be  treated  and  the  entire  mouth  restored  to  normal  health 
before  anything  is  done  in  the  way  of  substituting  artificial  for  the  nat- 
ural teeth. 

KETENTION  OR  EXTRACTION  OF  NATURAL  TEETH. 

It  would  be  difficidt  to  overestimate  the  value  of  a  thorough  prelimi- 
nary examination  of  the  mouth  for  which  an  artificial  dentiu-e  is  required, 
if  it  only  served  to  settle  the  various  questions  arising  in  relation  with 
any  natural  teeth  and  roots  which  remain  in  place.  These  teeth  and 
roots  must  be  considered  carefully  in  the  light  of  the  future  comfort  of 
the  patient,  as  well  as  in  their  bearing  upon  the  work  of  the  operator. 
There  is  probably  no  greater  problem  in  prosthetics  than  that  presented 
in  such  cases,  nor  one  reciuiring  the  exercise  of  more  judgment.  In 
some  mouths  there  T\-ill  be  presented  sound  roots  and  those  in  all  stages 
of  decay,  teeth  with  vital  pulps  and  those  with  pulps  no  longer  li^■ing. 
If  the  roots  are  healthy,  are  they  suitable  for  crowning,  and  will  crown- 
ing be  of  advantage  to  the  patient  ?  Will  the  roots  if  properly  treated 
and  crowned  be  of  se^^-ice  in  mastication,  or  will  the  artificial  crowns 
themselves  eventually  produce  pathological  conditions  ending  in  destruc- 
tion of  the  roots?  Are  the  vital  teeth  present  of  prospective  value  suffi- 
cient to  force  their  retention  in  the  mouth?  Will  the  \-ita\  teeth  aid  in 
the  retention  of  the  plate  or  prove  an  unending  annoyance  to  the  patient  ? 
These  are  queries  which  must  be  carefully  considered  and  answered  in 
all  preliminary  examinations. 

It  is  clearly  good  practice  to  first  extract  all  the  teeth  and  portions 
of  teeth  that  cannot  be  restored  to  health.  AMiether  teeth  and  roots 
which  are  healthy  or  may  be  made  healthy  are  to  be  retained  or  not  must 

.     18 


274  THE  STUDY  OF  THE  MOUTH. 

be  decided  by  two  considerations,  viz. :  whether  they  will  assist  in  the 
retention  of  the  denture  or  whether  they  will  interfere  with  its  adjust- 
ment. 

^Vhile  the  retention  of  artificial  dentures  is  not  the  subject  of  this 
chapter,  it  assumes  preliminary  importance  here  in  considering  the 
extraction  of  roots  and  vital  teeth.  The  retention  of  a  plate  is  a  matter 
of  so  great  importance  that  the  operator  who  fails  to  take  this  into  con- 
sideration invites  defeat.  It  is  well  understood  that  a  full  upper  denture 
is  more  satisfactory  in  the  ease  with  which  it  is  maintained  in  place  than 
a  partial  plate.  The  adhesion  is,  as  a  rule,  adequate  in  the  former,  but 
in  the  latter  it  is  subject  to  many  disturbing  elements.  Very  dry  mouths 
interfere  with  retention,  but  this  is  not  a  common  condition  and  does  not 
need  extended  notice.  Where  it  does  exist,  it  is  not  an  insuperable 
obstacle.  ^Mouths  in  which  the  alveolus  has  been  entirely  resorbed,  as 
is  frequently  the  case  in  both  jaws,  present  more  serious  problems,  es- 
pecially in  the  case  of  the  lower  jaw.  Properly  constructed  plates  can, 
however,  be  made  of  rubber  for  such  cases  that  will  exhibit  remarkable 
adhesion.  While  these  are  frequently  made  heavy  to  overcome  dis- 
placement, this  is  not  absolutely  required,  provided  care  is  taken  to  adapt 
them  by  wide  flanges  to  meet  the  loose  tissues  subjacent  to  the  alveolar 
ridge. 

Greater  liberty  should  be  allowed  in  extraction  in  a  mouth  favorable 
to  plate  retention,  while  great  conservatism  should  be  observed  in  cases 
in  which  stable  retention  of  the  plate  is  doubtful. 

^'ital  teeth  may  be  of  value  as  supports  either  in  bridge-work  or  in 
plates,  but  in  some  instances  they  interfere  with  the  stability  of  the 
artificial  substitute.  It  will  probably  be  wise  to  retain  these  as  long  as 
possible,  but  too  much  should  not  be  expected  in  the  way  of  their  reten- 
tion. The  idea  prevails,  not  only  with  patients  but  ^^^th  some  dentists, 
that  artificial  dentures  cannot  be  used  with  the  same  satisfaction  in  crush- 
ing articles  of  food  as  natural  teeth.  Greater  force  can  be  applied  wit\\ 
the  latter  it  is  true,  but  the  extremity  of  force  is  not  needed  in  mastica- 
tion, and  all  food,  of  whatever  kind,  can  be  comminuted  satisfactorily 
with  a  properly  arranged  set  of  artificial  teeth. 

The  permanency  of  all  isolated  teeth  and  roots  is,  and  must  always  be, 
a  question  of  doubt.  With  adjoining  teetli  lost  and  resorption  of  the 
alveolus  taking  place  continually,  the  tissues  surrounding  the  isolated 
tooth  must  eventually  give  way,  the  pericementum  becomes  detached, 
and  the  result  is  eventually  the  loss  of  the  tooth.  This  apj)lies  to  all 
teeth  and  is  one  great  obstacle  to  the  permanency  of  bridge-work. 
There  are  cases,  however,  when  an  isolated  molar  is  of  great  service  to 
the  operator,  for  a  well-advised  clasp  upon  it  may  stay  the  plate  and 
add  materially  to  the  patient's  comfort. 

It  is  difficult,  therefore,  to  give  any  opinion  except  in  general  terms  as 
to  the  advisability  of  the  extraction  or  retention  of  indiN'idual  vital 
teeth.  Each  one  must  be  judged  by  existing  conditions.  If  canine 
teeth  can  be  retained,  they  have  a  distinct  value  in  giving  form  to  the 
jaw  which  is  not  easily  obtained  by  artificial  substitutes.     Even  the 


RETENTION  OR  EXTRACTION  OF  NATURAL  TEETH.         27 o 

canine  roots  may  be  better  treated  and  crowned  than  extracted.  It  is 
time  wasted  to  attempt  to  save  a  single  anterior  tooth.  Any  isolated 
incisor  is  useless  for  appearance  or  for  mastication,  and  it  is  extremely 
difficult  to  align  artificial  teeth  mth  it  satisfactorily. 

Roots  crowned,  except  in  rare  instances,  are  of  doubtful  value  beyond 
temporary  expedients.  They  may  have  a  life  of  a  few  years,  but  e\'ent- 
ually  they  are  brought  to  the  forceps.  This  is  due  to  positive  patholog- 
ical conditions  engendered  by  undue  strain  on  the  peridental  membrane, 
or  by  direct  irritation  through  the  bands  of  the  crow-ns  and  sometimes 
from  imperfect  root  treatment. 

There  are  not  infrequently  cases,  however,  where  roots  should  be 
retained,  especially  in  the  anterior  portion  of  the  mouth.  With  care 
in  their  preparation  for  crowning  these  may  be  made  of  great  value  as  a 
support  to  the  artificial  plate  in  mastication.  Judgment  is,  however, 
necessary  here,  for  the  root  or  roots  must  be  of  the  best  quality  and 
capable  of  being  placed  in  perfect  hygienic  condition;  otherwise  their 
retention  would  be  a  mistake  and  result  unhappily. 

Whatever  may  be  decided  upon  in  this  preliminary  stage  must  be 
thoroughly  done.  If  extraction  is  chosen,  this  leaves  a  socket  of  tempo- 
rary bone  tissue  with  sharp  and  friable  edges,  which  becomes  inflamed 
and  may  become  infected  if  pains  are  not  taken  to  prevent  it.  All  the 
gums  should  be  carefully  bathed  with  an  antiseptic  wash,  the  sockets  of 
extracted  teeth  painted  with  tincture  of  iodine  or  a  1  per  cent,  solution 
of  formaldehyde.  This  latter  should  be  carefully  prepared  to  insure 
its  being  strictly  1  per  cent.,  for  beyond  this  strength  it  is  very  irritating. 
In  case  of  excessive  bleeding  tannic  acid  may  be  effectively  used,  either 
in  pow^der  or  in  solution,  the  latter  being  preferred.  Some  operators 
recommend  cutting  away  the  exposed  portions  of  the  alveolus,  but  as 
this  is  a  painful  operation  and  is  not  absolutely  necessary,  it  is  usually 
better  to  leave  the  resorption  to  nature.  A  mild  antiseptic  wash  should 
be  used  by  the  patient  three  times  a  day  until  healing  of  the  tissues  has 
occurred. 

Length  of  Time  to  Supervene  After  Extraction. — The  length  of 
time  it  is  necessary  to  wait  before  a  so-called  permanent  denture  can  be 
prepared  is  a  matter  that  can  only  be  discussed  in  general  terms.  If  the 
insertion  of  the  denture  is*  deferred  until  the  last  spicula  of  alveolar 
process  is  disposed  of  by  resorption,  it  may  be  years  before  the  final 
settling  of  the  artificial  denture  upon  the  bone  of  the  jaw  or  jaws  is 
attained.  It  is  not  only  necessary  to  wait  for  this  final  resorption,  but 
it  is  not  advisable  to  wait  at  all,  for  the  process  of  resorption  proceeds 
more  satisfactorily  if  a  temporary  plate  or  plates  be  inserted. 

It  Mill  be  necessary  to  wait  if  possible  a  week  after  the  extraction  of 
useless  teeth  has  been  completed  to  permit  partial  healing  of  the  irri- 
tated tissues.  The  exact  time  must  depend  upon  the  judgment  of  the 
operator.  There  are  cases  where  shock  supervenes  after  extraction, 
and  it  is  not  unusual  to  be  obliged  to  defer  all  operations  for  a  series 
of  weeks.  As  a  general  rule  a  temporary  denture  may  be  prepared  in 
the  time  first  named. 


276  THE  STUDY  OF  THE  MOUTH. 

The  question  of  a  temporary  plate  having  been  settled  between  the 
dentist  and  the  patient,  further  proeedure  must  be  left  to  the  judgment 
of  the  operator.  A  temporary  denture  is  not  supposed  to  be  of  mueh 
value  in  mastieation,  the  sharp  edges  of  the  alveolar  processes  forbidding 
this.  This  condition  frequently  suggests  the  surgical  operation  of  re- 
moving these  projecting  points  with  bone-cutting  forceps.  It  is  not 
uncommon,  however,  for  temporary  sets  to  be  so  satisfactory  to  the 
wearer  that  they  are  continued  in  use  for  years.  They  are  not  supposed 
to  be  in  use  for  more  than  one  year,  when  a  more  comfortable  plate  can 
be  inserted;  but  even  this  must  assume  a  semi-temporary  character,  for 
this  resorption  of  the  process  is  continuous  until  all  the  alveolus  is  re- 
moved, and  this  covers  an  uncertain  period. 

The  method  of  taking  an  impression  for  these  temporary  dentures 
does  not  differ  from  that  ordinarily  employed,  })ut  while  some  use  other 
materials  in  general  prosthetic  practice  for  this  purpose,  plaster  alone 
should  l^e  used  here,  and  for  the  excellent  reason  that  the  tissues  sur- 
rounding the  extracted  teeth  are  left  in  a  soft,  flabby  condition  which 
any  impression  material  requiring  force  will  displace.  Aside  from  this, 
it  is  well  to  have  the  sockets  of  the  extracted  teeth  produced  on  the 
cast  when  the  artificial  teeth  are  ground  to  fit  the  gum. 

It  is  sometimes  demanded  by  patients  that  the  natural  teeth  all  re- 
main in  place  until  the  temporary  set  is  completed.  ^Yhen  this  is  the 
case  it  will  be  necessary  to  take  an  impression  of  the  mouth  before  the 
teeth  are  extracted,  when  the  plaster  teeth  are  cut  ofi"  the  cast,  and  their 
sockets  carved  out  to  represent  resorption.  This  is  freciuently  resorted 
to,  but  cannot  be  recommended  for  all  cases,  although  it  may  be  used 
to  advantage,  for  example,  in  a  case  for  which  a  partial  plate  is  to  be 
inserted  after  the  removal  of  the  six  anterior  teeth. 

An  impression  in  plaster  should  first  be  secured.  This  will  give  the 
operator  the  exact  form  and  position  of  the  natural  teeth  and  enable  him 
to  reproduce  them  with  greater  satisfaction  to  the  patient,  who  is  always 
naturally  sensitive  to  any  marked  change  of  appearance.  After  the 
length,  size,  and  position  of  the  natural  teeth  have  been  carefully  noted, 
they  may  be  cut  from  the  plaster  reproduction,  and  then  the  cast  carved 
to  represent  the  possible  resorption  certain  to  follow  after  extraction. 
A  better  way,  however,  is  to  take  another  impression  after  extraction 
and  to  use  this  to  prepare  the  base  for  the  temporary  set.  Plain  teeth 
will  be  required  here,  and  these  must  be  arranged  in  anticipation  of  the 
great  amount  of  resorption  sure  to  follow.  Such  a  plate  belongs  entirely 
in  the  category  of  temporary  dentures  and  should  be  replaced  inside  the 
year.  All  temporary  plates  of  the  kind  described  have  a  value  besides 
inviting  by  pressure  more  rapid  resorption  of  the  alveolar  process,  and 
that  is  their  binding  effort  upon  the  tissues,  retaining  them  in  position 
and  protecting  them  from  the  continued  irritation  which  would  other- 
wise occur  in  mastication. 

It  is  possible  that  in  rare  instances  surgical  interference  may  be 
necessary  in  removing  adhesions  of  cicatricial  tissue,  but  these  are  not 
likely  to  occur  where  temporary  sets  are  inserted  soon  after  extraction. 


SURGICAL  COMPLICATIONS.  277 

and  even  should  such  take  place,  it  has  been  the  experience  of  the 
writer  that  the  plate  soon  finds  its  proper  bed,  removing  at  the  same 
time  all  trouble  from  adhesions.  Patients  are  very  sensitive  to  the 
thought  of  a  surgical  operation,  and  this  should  be  adopted  only  as 
the  last  resort. 

SURGICAL  COMPLICATIONS. 

The  complications  that  may  precede  or  follow  the  preparation  of  the 
mouth  for  an  artificial  denture,  while  briefly  alluded  to  on  previous 
pages,  demand  a  more  detailed  discussion.  After  the  removal  of  teeth, 
whether  firmly  implanted  or  where  inflammatory  conditions  have  pro- 
duced a  loosening  of  their  attachment,  there  is  more  or  less  swelling  of 
the  gum  which  interferes  with  the  correctness  of  any  impression  taken 
immediately.  This  necessitates  delay  to  permit  these  abnormal  condi- 
tions to  subside  before  attempting  the  insertion  of  an  artificial  substi- 
tute. 

Inflammation. — Where  many  teeth  are  to  be  removed,  the  possi- 
bility of  subsequent  inflammation  is  increased  in  direct  proportion 
to  the  number  of  teeth  involved.  It  is  important  that  the  tissues 
surrounding  the  teeth  should  be  carefully  protected  from  injury.  The 
careless  handling  of  the  forceps  may  not  only  produce  unnecessary 
sufi^ering  to  the  patient,  but  may  be  the  cause  of  subsequent  com- 
plications in  the  preparation  of  the  denture.  After  the  extracting 
has  been  done,  care  should  be  taken  to  discover  if  any  portion  of  the 
alveolus  is  fractured  and  all  loose  pieces  should  be  carefully  removed. 
Pendant  portions  of  the  gum,  the  result  of  previous  inflammatory  condi- 
tions, or  brought  about  by  the  operation,  should  be  removed,  as  their 
presence  delays  the  healing  process.  The  removal  of  portions  of  the 
alveolus  by  a  subsequent  operation  has  pre\dously  been  alluded  to,  and 
while  not  imperative,  may  sometimes  be  resorted  to  with  advantage  to 
both  patient  and  operator.  Before  attempting  this,  however,  the  con- 
sent of  the  patient  should  be  obtained,  for  while  not  a  serious  operation, 
it  involves  some  pain  and  subsequent  soreness.  For  this  reason  many 
prosthetic  practitioners  prefer  to  await  the  slower  process  of  resorption. 
If,  however,  a  surgical  operation  seems  necessary,  it  must  be  performed 
under  a  local  anaesthetic  such  as  cocaine,  or  under  nitrous  oxide  and 
oxygen,  and  be  followed  by  the  use  of  an  antiseptic  mouth-wash. 
Whether  the  surgical  procedure  be  adopted  or  the  slower  process  of 
resorption  be  allowed  to  take  place,  this  antiseptic  washing  of  the  mouth 
should  be  continued  by  the  patient  during  the  period  of  healing. 

Temporary  Denture. — Should  it  be  necessary  to  insert  a  temporary 
denture  immediately  after  the  teeth  are  removed,  and  this  not  infre- 
quently happens,  it  will  be  necessary  to  follow  a  somewhat  difterent 
procedure  from  that  described  on  a  preceding  page.  To  prepare  such 
a  denture  immediately  after  extraction  involves  many  difficulties. 
Any  attempt  to  secure  an  impression  from  which  a  plate  at  all  permanent 
in  character  can  be  made  must  necessarily  be  futile,  as  the  inflamed 
condition  of  the  gums  renders  this  impossible.     A  plate  made  at  this 


278  THE  STUDY  OF  THE  MOUTH. 

time  will,  therefore,  as  a  rule,  be  of  a  strictly  temporary  nature,  and  this 
should  be  distinctly  understood  by  the  patient. 

To  secure  a  correct  impression,  plaster  alone  should  be  used.  While 
opinions  may  differ  as  to  the  use  of  this  agent  under  other  conditions, 
there  can  be  but  one  opinion  as  to  its  use  for  these  cases,  for  it  will,  if 
properly  prepared,  cause  little  or  no  displacement  of  the  parts,  and  re- 
produce them  with  an  exactness  not  possible  with  any  other  material. 
It  is  very  important  that  protruding  portions  of  the  gums  should  not  be 
disturbed,  and  those  remaining  in  place,  in  cases  in  which  it  has  not  been 
deemed  wise  to  remove  them  surgically,  should  be  reproduced  on  the 
cast  upon  which  the  plate  is  to  be  made. 

The  insertion  of  the  temporary  denture  is  not  ordinarily  productive 
of  discomfort  to  the  patient.  The  close  adaptation  of  the  base  to  the 
gum  tissue  serves  as  a  binding  bandage  and  will,  by  its  continuous  pres- 
sure, hasten  the  healing  of  the  irritated  areas.  The  time  such  a  denture 
may  be  worn  will  vary  and  cannot  be  predetermined  with  accuracy ;  but 
when  properly  prepared,  may  serve  for  a  long  time  with  comfort  to  the 
wearer,  and  even  in  some  rare  instances  take  the  place  of  a  permanent 
plate.  It  is  not,  however,  advisable  to  continue  its  use  for  more  than 
a  year,  as  complications  may  result  which  will  interfere  with  the  more 
perfect  adaptation  of  the  permanent  denture. 

Adhesions. — There  is  occasionally  found  a  cicatricial  adhesion  be- 
tween the  mucous  membrane  of  the  cheek  and  that  of  the  aheolar  wall. 
This  may  be  a  cord-like  attachment  which  marks  the  site  of  the  fistulous 
opening  of  a  previous  aheolar  abscess.  The  adhesion  may  be  the  result 
of  extraction,  the  loosened  tissue  falling  into  the  wound  and  becoming 
attached  as  a  result.  This  may  not  be  so  situated  as  to  call  for  surgical 
interference,  but  if  it  does  interfere  with  the  proper  setting  of  the  plate 
and  endangers  its  stability,  it  should  be  removed.  Wounds  of  the 
mouth,  whether  incised  or  from  the  use  of  caustics,  may  in  healing  cause 
extensive  attachments  between  the  cheek  anfl  alveolus,  rendering  the 
wearing  of  a  plate  difficult  or  impossible.  This  condition  must  also  be 
treated  before  a  denture  is  inserted. 

The  surgical  principal  invohed  in  the  procedure  is  to  produce  a  separa- 
tion of  the  parts  and  to  continue  this  separation  by  the  insertion  of  a 
plate  which  will  prevent  contact  of  the  parts  and  consequently  a  reunion 
of  the  tissues.  This  operation  may  require  local  anesthesia  for  its  per- 
formance unless  it  be  of  minor  character;  the  use  of  a  4  per  cent,  solution 
of  cocaine  will  be  found  satisfactory  for  the  purpose.  The  incised  parts 
should  be  washed  with  an  antiseptic  solution.  The  surface  may  be 
painted  with  styptic  collodion. 

If  the  adhesions  are  extensive,  it  will  be  found  preferable  to  first  take 
an  impression  of  the  mouth  and  prepare  a  cast  for  stud>'.  The  cast  is 
then  cut  away  as  is  proposed  by  the  surgical  operation,  and  a  plate  with- 
out teeth  prepared  from  it.  The  plate  should  be  inserted  in  the  mouth 
immediately  after  the  operation  to  prevent  the  readhesion  of  the  parts. 
A  styptic  should  be  applied  after  the  operation;  a  spray  of  hydrogen 
peroxide  usually  checks  hemorrhage.    If  this  does  not  suffice,  a  solution 


CHOICE  OF  BASE.  279 

of  tannin  will  usually  be  found  effective.  The  cut  surfaces  may  be  dried 
with  pieces  of  lint  and  painted  with  styptic  collodion;  as  soon  as  this 
is  dry  the  plate  should  be  inserted.  The  patient  must  be  directed  to 
wash  the  mouth  several  times  a  day  with  an  antiseptic,  such  as  veruas, 
listerine,  or  1  per  cent,  solution  of  hydronaphthol.  The  irritatinji; 
character  of  the  latter  must  be  carefully  noted  and  its  use  discontinued 
if  the  irritation  is  marked.  This  plate  is  simply  placed  in  position  to 
promote  healing  and  prevent  adhesion  of  the  cut  parts,  and  it  should  not 
be  required  to  be  in  place  more  than  two  weeks.  Should  the  granulated 
surfaces  show  an  unhealthy  appearance,  they  should  be  painted  with 
a  solution  of  nitrate  of  silver,  4  grains  to  the  ounce.  Tincture  of  iodine 
may  also  be  found  effective  painted  upon  the  gums. 

CHOICE   OF  BASE. 

The  importance  of  the  selection  of  a  proper  base  for  the  artificial 
denture  cannot  be  overestimated.  Each  case  under  consideration  calls 
for  careful  study,  and  each  presents  a  problem  not  easy  of  solution. 
Vulcanite,  celluloid,  gold,  silver,  platinum,  aluminum,  certain  alloj^s  of 
tin,  known  as  "fusible  alloys,"  and  porcelain  have  all  been  used  as  a 
base  for  the  denture.  A  consideration  of  the  merits  of  each  of  these 
materials  will  now  be  in  order.  Vulcanite  is  the  material  in  most  com- 
mon use  for  full  sets,  and,  while  not  a  perfect  material,  justly  deserves 
a  prominent  position  in  the  list  if  care  is  taken  to  overcome  its  disad- 
vantages. 

Under  the  early  conditions  of  its  use  a  serious  objection  to  vulcanized 
rubber  developed.  In  some  cases  it  was  liable  to  produce  inflammation 
of  the  mucous  membrane,  or  what  was  known  as  "rubber  sore  mouth." 
This  pathological  condition,  manifesting  itself  shortly  after  vulcanite 
was  introduced  as  a  base  for  artificial  teeth,  became  a  problem  to  dentists 
and  a  source  of  much  complaint  on  the  part  of  the  medical  profession. 
So  serious  did  this  objection  become  that  it  threatened  to  destroy  the 
usefulness  of  this  material  in  dentistry.  The  question  was  taken  up 
by  the  Pennsylvania  Association  of  Dental  Surgeons  in  the  early  sixties, 
and  it  was  given  over  to  Professors  Wildman,  Buckingham,  and  Tru- 
man to  find,  if  possible,  any  ground  for  the  charge  that  the  inflamma- 
tion was  the  result  of  mercuric  action  arising  from  some  chemical  change 
in  the  vermilion  used  in  coloring  the  rubber.  This  research  committee 
in  its  final  report  proved  conclusively  that  mercury  had  nothing  to  do 
with  the  pathological  condition  in  question.  In  their  opinion  it  was 
due  in  part  to  the  non-conductivity  of  the  rubber,  and  possibly,  in 
addition,  to  the  rough  surface  left  after  vulcanization,  which  retained 
food  particles  in  close  proximity  to  the  mucous  membrane,  exciting  by 
their  presence  inflammatory  processes.  This  latter  conclusion  was  con- 
sequently confirmed  by  Black,  who  demonstrated  that  this  condition 
invited  microbic  development,  and  the  presence  of  toxic  matter  derived 
from  this  source  produced  the  result  complained  of  so  universally.  It 
had  been  demonstrated  that  metal  as  a  base  could  be  tolerated  by  the 


280  THE  STUDY  OF  THE  MOUTH. 

membrane  without  producing  undue  irritation,  and  this  was  explained  by 
its  superior  thermal  conductivity  and  the  fact  that  its  polisiicd  surface 
prevented  accretions. 

This  was  so  positively  manifest  in  the  use  of  metal  plates  tiiat  pros- 
thetic workers  adopted  the  use  of  tin  foil  placed  over  the  cast  before 
vulcanization.  This  became  imbedded  in  the  rubber  and  upon  removal 
left  the  surface  highly  polished,  requiring  only  the  revolving  brush  to 
complete  it.  This  was  found  largely  to  overcome  the  trouble  heretofore 
experienced,  and  vulcanite  as  a  base  has  become  almost  universal  for 
ordinary  sets.  Its  superior  quality  of  lightness,  comparative  ease  of 
manipulation,  and  adaptability  to  all  conditions  of  the  mouth,  and, 
above  all,  its  hygienic  possibilities  brought  it  into  general  use. 

The  introduction  of  rubber  as  a  base  for  artificial  teeth  resulted  in  a 
revolution  in  prosthesis.  The  old  methods  of  soldering  were  practically 
abandoned,  with  the  result,  natural  to  such  sudden  changes,  of  much 
inferior  work.  The  merits  and  demerits  of  the  material  were  not  under- 
stood, nor  were  the  proper  methods  to  be  observed  in  its  use  fully  known. 
The  material  is  still  much  abused  at  the  present  time. 

The  committee  of  the  Pennsylvania  Association,  previously  alluded 
to,  demonstrated  by  careful  research,  microscopical  and  chemical,  that 
rubber  if  properly  vulcanized  would  not  absorb  the  fluids  of  the  mouth. 
Whether  absorption  would  take  place  under  a  greater  pressure  than  is 
present  in  the  vulcanizer  remains  yet  to  be  proved ;  but  no  plate  exam- 
ined gave  any  evidence  of  moisture,  nor  was  imbibition  possible  under 
ordinary  mouth  conditions,  the  vulcanite  being  absolutely  impervious. 
This  applies,  however,  only  to  properly  vulcanized  rul)ber.  There  is 
doubtless  much  vulcanite  inserted  in  mouths  so  porous  as  to  become 
positively  foul  from  the  absorbed  fluids  and  the  decomposition  of  organic 
matter,  resembling  in  this  respect  the  early  walrus  carved  specimens 
which  are  interesting  now  only  as  exhibits  in  dental  museums. 

Aside  from  its  value  for  entire  sets,  it  is  even  more  important  in  attach- 
ing teeth  to  gold  or  platinum  plates,  completely  relegating  the  older 
processes  of  backing  and  soldering  to  ancient  history,  and  adding  there- 
by not  only  to  the  comfort  but  to  the  health  of  the  wearers. 

While  the  non-conductivity  of  vulcanite  is  the  main  objection  to  its 
use  for  entire  plates,  this  does  not  apply  to  rubber  attachments  on  metal. 

The  gold  base  is  still  extensively  used  for  a  superior  class  of  work. 
For  full  dentures  it  is  usually  employed  as  the  base-plate  proper  with  the 
teeth  attached  by  means  of  vulcanite.  This  type  of  denture  ranks  next 
to  that  of  continuous-gum  in  its  hygienic  qualities,  its  aesthetic  possibili- 
ties, and  its  general  acceptability  to  the  mucous  membrane.  Its  ability  to 
transmit  thermal  changes,  its  highly  polished  and  hence  easily  cleaned 
surface,  and  its  freedom  from  interstices  in  which  foreign  matter  might 
find  lodgment,  account  for  its  general  hygienic  value.  The  relative 
thinness  of  the  base-plates  and  its  strength,  its  unalterable  character  in 
the  mouth,  and  the  possibility  of  any  desired  arrangement  of  the  teeth 
in  the  vulcanite  attachment  are  all  advantages  associated  with  this 
type  of  denture. 


CHANGE  OF  BASE.  281 

Because  of  the  relatively  high  cost  of  the  material  it  is  not  customary 
to  insert  full  gold  dentures  until  at  least  a  year  after  the  last  teeth  have 
been  extracted,  to  allow  the  greater  portion  of  the  resorption  to  occur. 

Gold  offers  many  advantages  for  partial  plates  and  is  to  be  pre- 
ferred in  most  instances.     Where  much  strength  is  required,  as,  for  ex- 
ample, when  some  of  the  teeth  to  be  replaced  are  isolated,  it  is  impossible 
to  secure  the  desired  strength  in  vulcanite. 

Sih-er  was  the  ordinary  base  for  temporary  dentures  in  former  years 
by  reason  of  its  cheapness ;  it  was  also  used  for  permanent  plates  for  the 
same  reason.  Where  cheapness  in  a  full  metal  plate  is  now  desired, 
swaged  aluminum  has  come  into  general  use  for  this  purpose. 

With  the  development  of  exact  methods  of  casting,  cast  aluminum 
base-plates  have  also  become  a  useful  addition  to  our  list  of  cheaper 
metal  base-plates.  Opinion  is  divided  as  to  whether  they  are  as  satis- 
factory as  the  swaged  plate,  but  it  is  likely  that  if  careful  attention  is 
given  to  the  technic  of  making,  they  will  be  equally  useful. 

For  the  lower  jaw,  as  before  stated,  weight  in  the  denture  may  be 
necessary.  Base-plates  cast  of  any  of  the  fusible  alloys  recommended 
for  this  purpose  will  usually  prove  quite  satisfactory. 

Where  something  better  than  the  metals  ordinarily  used  is  desired, 
the  porcelain  continuous-gum  denture  may  be  employed  with  great 
satisfaction,  combining  as  it  does  artistic  beauty,  cleanliness,  and 
weight. 

The  high  aesthetic  quality  of  the  continuous-gum  denture,  its  freedom 
from  crevices  in  which  foreign  matter  may  be  retained,  and  its  highly 
polished  surface,  unalterable  in  the  mouth,  recommend  it  strongly  in 
suitable  cases. 

Celluloid  has  practically  become  obsolete  as  a  material  for  dental 
plates  because  of  inherent  defects  in  the  material. 


CHAPTER    VII. 

IMPRESSIONS  OF  THE   MOUTH. 

By  a.  DeWitt  Gritman,  D.  D.  S. 

The  first  step  incident  to  the  construction  of  a  successful  denture, 
and  one  that  does  not  always  receive  proper  consideration,  is  to  obtain 
a  perfect  plaster  reproduction  of  the  jaw  for  which  the  denture  is 
intended,  and  this  requires  that  an  accurate  impression  of  the  same  be 
taken. 

The  impression  of  the  edentulous  mouth,  or  of  one  requiring  a  partial 
substitute,  has  been  defined  variously  at  the  several  stages  in  the 
development  of  prosthetic  dentistry.  In  the  earlier  periods  it  was  re- 
garded as  quite  sufficient  to  have  a  counterpart  of  the  mouth  made 
with  softened  wax  (beeswax),  and  the  impression  was  ordinarily  taken 
without  much  regard  to  the  conditions  relating  to  the  retention  of  the 
plate. 

The  present  aim  in  all  impression  taking  is  the  ultimate  perfect  adap- 
tation of  the  plate,  and  in  order  to  accomplish  this  a  thorough  study  of 
the  mouth  is  a  prerequisite;  without  this  adaptation  a  comfortable 
denture  is  not  to  be  expected.  Each  mouth  requires  separate  study, 
and  no  absolute  rule  can  be  laid  down  which  will  be  of  general  value. 
The  condition  of  the  soft  tissues,  the  various  abnormal  growths,  the 
possibility  of  retention,  especially  in  the  lower  jaw,  the  difficulty  of 
overcoming  in  some  persons  the  nausea  consequent  upon  a  foreign  body 
being  placed  in  the  mouth — all  these  details  must  be  considered;  in 
fact,  no  impression  should  be  attempted  before  every  unfavorable 
condition  has  been  studied  and  provision  made  to  overcome  it. 

An  impression  of  the  mouth,  in  the  modern  acceptation  of  the  term, 
means  the  first  step  in  the  successful  retention  of  the  denture,  and  in 
order  that  this  may  be  accomplished  there  should  be  a  careful  study  of 
the  appliances  and  materials  used  for  this  purpose.  ^ 

Impression  Materials. — In  order  that  the  impression  shall  be  an  exact 
counterpart  of  the  jaw,  a  suitable  material  to  eft'ect  it  is  demanded. 
To  answer  the  requirements  of  such  usage,  the  material  must  readily 
become  plastic  and  pliable  at  a  temperature  not  injurious  to  the  tissues 
of  the  oral  cavity.  It  must  copy  accurately  the  irregular  surfaces  of 
the  jaw,  and  with  equal  accuracy  retain  its  form  after  the  impression 
has  been  removed  from  the  mouth.  It  must  also  harden  in  less  than 
five  minutes.  It  should  neither  contract  nor  expand.  The  perfect 
impression  material  has  never  been  produced,  and  prosthetic  operators 
are  compelled  to  make  use  of  present  materials — viz.,  plaster  of  Paris, 
modelling  compound,  beeswax,  and  gutta-percha.  These  substances 
group  themselves  into  two  classes  of  materials  commonly  used  for  this 
purpose:  one  made  into  a  plastic  mass  with  water,  and  the  other  through 

282 


IMPRESSION  MATERIALS.  283 

the  action  of  heat.  The  first,  plaster  (phister  of  Paris),  is  generally 
considered  to  have  the  greatest  number  of  qualities  recommending  it 
to  use.  In  proportion  to  the  difficulty  connected  with  the  impression 
will  plaster  be  found  the  best  material  to  use. 

IMPRESSION  MATERIALS. 

"Wax. — This  is  a  solid  of  animal  and  vegetable  origin.  Of  wax  from 
the  animal  sources  there  are  beeswax,  Chinese  insect  wax,  and  sperma- 
ceti. The  vegetable  waxes  are  Japanese  wax,  myrtle-berry  wax,  palm 
wax,  etc. 

Beeswax  is  secreted  by  all  honey  bees,  and  by  them  formed  into  the 
cell-walls  of  their  honeycomb.  It  is  this  that  was  formerly  the  only 
material  suitable  for  impressions,  and  the  older  practitioners  of  dentistry 
were  forced,  in  the  absence  of  better  material,  to  prepare  this  from  the 
mass  furnished  through  the  general  markets.  It  is  now  prepared  by  the 
supply  houses  in  convenient  cakes  ready  for  manipulation. 

Beeswax  is  softened  either  by  dry  heat  or  in  hot  water,  and  is  then 
kneaded  into  a  doughy  mass  and  applied  as  an  impression  material  in 
proper  trays.  It  is  not  a  satisfactory  material  for  this  purpose,  as  it 
does  not  make  a  sharp  impression,  leaving  a  degree  of  uncertainty  as  to 
the  final  result.  This  fact  has,  therefore,  placed  it  among  the  obsolete 
impression  materials,  but  it  has  not  been  entirely  driven  from  the 
prosthetic  laboratory,  where  it  still  fills  a  proper  place  in  many  of  the 
minor  operations  arising  in  practice.  While  springs  were  used  in  full 
dentures,  wax  served  imperfectly  to  give  a  reproduction  of  the  jaw. 
Since'  springs  have  become  obsolete,  and  dependence  on  adhesion 
is  the  main  reliance,  beeswax  has  been  abandoned  as  an  impression 
material  except  in  rare  instances.  Various  combinations  have  been 
prepared  to  take  its  place  as  a  heat-softened  material.  The  most 
prominent  of  these  is  what  is  termed 

Modelling-  Compound. — This  is  a  material  prepared  to  take  the  place 
of  beeswax,  as  described.  It  is  composed  of  a  resinous  gum,  such  as 
copal,  dammar,  or  kauri,  with  stearin,  French  chalk,  colored  and 
flavored. 

A  formula  of  Mr.  E.  Lloyd  Williams,  of  London,  England,  is  as  follows: 
"French  chalk,  one  and  three-quarter  parts;  kauri,  one  part;  stearin, 
one  and  a  half  parts.  j\Ielt  the  stearin  in  an  enameled  pan  and  stir 
in  the  gum.  When  these  are  thoroughly  incorporated,  stir  in  the  chalk. 
It  may  be  colored  with  carmine  and  flavored  as  desired." 

The  Use  of  Modelling  Compound. — A  proper  tray  having  been  selected, 
a  sufficient  quantity  of  the  modelling  compound  is  taken  and  softened 
by  dry  heat  and  then  placed  in  the  tray,  previously  warmed.  ^  The 
surface  of  the  compound  is  then  slightly  softened  by  passing  it  over  the 
flame  before  it  is  inserted  in  the  mouth.  It  is  then  placed  in  the  posi- 
tion desired  and  pressed  well  into  place,  care  being  taken  that  all  parts 
of  the  compound  on  the  lateral  margins  are  pressed  by  the  index-finger 
into  all  the  irregularities  of  the  jaw.      This  completed,  the  compound 


284  IMPRESSIONS  OF  THE  MOUTH. 

is  left  in  the  mouth  to  harden.  This  process  may  he  hastened  hy  the  use 
of  cold  water  ejected  from  a  syringe  or  by  the  contact  of  an  aseptic 
napkin  saturated  with  water.  When  hard  it  is  removed  in  the  usual 
way,  by  slight  pressure  downward  if  in  the  upper  jaw,  and  upward  if 
in  the  lower.  The  removal  is  effected  with  far  less  difficulty  than  with 
])laster. 

Advantages  Claimed  for  the  Compound. — It  is  claimed  that  this  model- 
ling compound  takes  a  sharp  impression,  that  is  not  subject  to  fracture 
on  removal  and  that  it  compresses  the  soft  tissues.  These  are  true, 
but  it  must  be -remembered  that  a  sharp  impression  does  not  always 
mean  a  perfect  impression. 

Disadvantages. — The  force  required  to  insert  the  compound  necessarily 
disturbs  the  relation  of  the  soft  tissues  with  the  jaw,  and  as  these  are 
moved  from  what  may  be  termed  the  normal  position  a  more  or  less 
imperfect  impression  of  the  mouth  is  obtained.  The  operator  should 
aim  to  secure  a  perfect  duplication  of  the  tissues  in  situ,  and  this  is 
always  a  question  of  uncertainty  when  a  material  like  modelling  com- 
pound is  used.  It  is  true  that  in  skilled  hands  this  material  may  suc- 
ceed in  giving  apparently  excellent  results,  but  the  general  principles 
governing  all  operations  of  this  kind  must  be  carefully  adhered  to  if  the 
best  results  are  to  be  attained. 

The  following  quotation  gives  the  method  in  use  adopted  by  the  Green 
Brothers,  and,  as  this  seems  to  meet  fully  the  requirements  of  the 
material,  it  is  given,  in  part,  as  quoted  by  George  Henry  Wilson,  D.  D. 
S.,  in  his  "Manual  of  Dental  Prosthetics": 

"The  best  position  in  which  the  operator  may  stand  while  taking  this 
form  of  impression  is  directly  back  of  the  patient.  The  partially 
taken  impression  is  removed  from  the  mouth,  thoroughly  chilled,  and 
any  excess  removed.  The  peripheral  labial  and  buccal  borders  are 
warmed  over  a  small  weak  Bunsen  flame  and  quickly  returned  to  place 
in  the  mouth.  It  is  securely  held  in  place  with  one  hand,  and  while  the 
patient  is  muscle  trimming,  the  operator  makes  interrupted  compres- 
sion over  the  lips  and  cheeks  with  the  disengaged  hand.  It  may  be 
necessary  to  rewarm  and  muscle  trim  several  times,  or  an  addition  of 
soft  dry  compoimd  may  be  needed  upon  portions  of  the  rim  of  the 
impression.  This  addition  may  be  made  by  "  tracing  on"  with  a  stick 
of  compound.  When  the  operator  is  satisfied  that  the  rim  of  the  im- 
pression is  perfectly  adapted  backward  to  the  anterior  border  of  the 
molar  processes,  the  impression  is  thoroughly  chilled,  dried,  and  a  small 
roll  of  soft  modelling  compound  placed  along  the  palatal  border,  upon 
the  maxillary  surface,  and  extended  around  the  tuberosities  to  the  malar 
processes.  This  addition  is  made  quite  soft  in  the  small  Bunsen  flame, 
carried  into  the  mouth,  and  quickly  forced  into  place,  removed,  and 
dried.  If  it  has  not  been  sufficiently  compressed,  it  is  again  softened 
and  pressed  in  the  mouth.  The  impression  may  now  be  considered 
complete.  It  is  placed  in  cold  water  until  thoroughly  cold  and,  with- 
out dr\'ing,  it  is  replaced  in  the  mouth  and  very  firm  pressure  made 
upon  the  hngual  surface  of  the  tray  while  the  hp  and  cheeks  are  lifted 


IMPRESSION  MATERIALS.  285 

and  drawn  into  position  over  the  rim  of  the  impression.  The  finjijers 
are  removed  from  the  mouth  and  the  patient  requested  to  remove  the 
impression." 

The  various  uses  to  which  modelhng  compound  may  be  appHed  will 
be  described  under  the  proper  headings. 

Gutta-percha  (Isonandra  Gutta).— This  name  is  applied  to  the  con- 
creted or  inspissated  juice  of  various  plants.  The  geographical  dis- 
tribution of  the  trees  producing  this  is  very  restricted.  The  yield  of  a 
•well-grown  tree  is  from  two  to  three  pounds  of  gutta-percha.  Its  use 
in  the  arts  is  very  important,  but  is  much  restricted  in  dentistry,  al- 
though many  attempts  have  been  made  to  use  it  as  an  impression 
material.  It  makes  a  sharp  impression,  and  on  account  of  this  has 
been  much  used  in  the  taking  of  molds  for  electrotypes,  etc. 

Its  intractable  nature  has  relegated  it  to  other  purposes  than  that 
of  impressions  in  prosthetic  work.  Plaster  of  Paris  and  modelling 
compound  have  entirely  superseded  this  as  they  have  other  materials. 

The  base-plate  gutta-percha  is  furnished  by  the  supply  houses.  It 
is  not  the  pure  gum,  but  other  ingredients  are  mixed  with  it  to  give  it 
a  firmer  body.  This  is  used  principally  for  temporary  trial  plates  in 
the  mouth. 

Impression  Plaster. — Plaster  of  Paris  has  already  been  considered  as 
to  its  general  qualities,  but  for  use  in  this  connection  it  must  now  be 
given  more  detailed  attention.  This  is  a  special  grade  of  plaster,  very 
finely  ground,  and  setting  quickly.  Properly  mixed,  it  should  set  in 
about  three  minutes,  but  is  not  nearly  so  strong  as  casting  plaster,  which 
is  used  for  the  cast  and  flasking.  When  employed  for  impression  taking 
it  should  be  colored  and  flavored.  The  advantage  of  flavoring  it  is 
that  this  gives  greater  comfort  to  the  patient,  overcoming  the  disagree- 
able taste  of  plaster  and  reducing  the  tendency  to  nausea,  which  fre- 
quently interferes  with  absolute  accuracy  in  the  impression. 

Coloring  of  Plaster. — By  coloring  the  plaster  the  operator  is  enabled 
to  remove  it  more  readily  from  the  cast,  thus  reducing  the  danger  of 
mutilating  the  latter.  The  work  can  also  be  completed  more  quickly, 
and  time  is  an  important  factor  in  all  dental  operations. 

The  preparation  of  this  coloring  fluid,  as  used  by  the  writer,  is  as 
follows:  To  one  ounce  of  carmine  add  five  ounces  of  ammonia,  and, 
when  thoroughly  dissolved,  remove  the.  cork  and  allow  the  fumes  of 
ammonia  to  pass  off.  To  one  ounce  of  this  solution  add  one  ounce  of 
Roger  and  Gallet's  violet  water. 

While  impression  plaster  sets  in  a  comparatively  short  time,  it  is 
often  desired  to  hasten  this  in  order  to  reduce  the  period  during  which 
the  impression  must  be  held  in  the  patient's  mouth.  Each  batch  of 
plaster  should  be  tested  as  to  time  of  setting,  as  this  varies  in  different 
lots  of  the  same  brand. 

Several  methods  are  employed  to  hasten  the  setting  of  the  plaster. 
Potassium  sulphate  in  powder  or,  preferably,  as  a  saturated  solution 
of  crystals  is  effective.  Chloride  of  sodium  is  used  also  for  this  purpose. 
Warm  water  also  hastens  the  setting.     Each  of  these  methods  may  be 


286 


IMPRESSIONS  OF  THE  MOUTH. 


used,  depending  upon  the  grade  of  plaster  and  the  time  desired  for  the 
completion  of  the  setting  process.  The  method  used  by  the  writer  is, 
first,  to  place  five  drops  of  the  coloring  material  in  a  bowl,  then  a 
half  teaspoonful  of  a  saturated  solution  of  potassium  sulphate.  The 
amount  of  water  necessary  for  the  average  impression,  from  one  to  one 
and  a  half  ounces,  is  then  added.  The  plaster  is  now  sifted  in  carefully 
until  the  water  has  been  completely  taken  up  by  the  plaster.  Then 
the  plaster  spatula  is  cut  back  and  forth  through  the  mass  to  eliminate 
any  air  bubbles.  Stirring  the  plaster  will  hasten  its  setting.  The 
proper  consistency  of  the  mix  for  taking  the  impression  is  attained  when 
the  batter  on  the  tray  is  thick  enough  to  permit  inserting  the  latter 
without  danger  of  the  plaster  dropping. 

PLASTER  IMPRESSIONS. 

Plaster  Spatula  and  Bowl.-  The  form  of  spatula  shown  in  Fig.  244 

was  designed  to  serve  two  purposes.     It  presents  at  its  point  two  corners, 

one  round  and  the  other  square.     The  round  corner  is  used  in  mixing 

the  plaster,  and  the  other  is  best   adapted  for  shaping  up  the  cast  on 

Fig.  244. 


Plast 


atula. 


the  glass  slab.  The  plaster  can  be  so  shaped  with  it  that  there  is  very 
little  need  of  trimming  after  it  has  hardened.  The  square  corner  is 
also  useful  and  a  great  time  saver  in  flasking,  and  will  leave  the  plaster 
in  proper  shape  to  be  varnished. 

The  plaster  bowl  made  from  rubber  (Fig.  245)  is  now  more  generally 
used  than'that  of  porcelain  or  metal.    The  advantages  of  the  porcelain 

Fig.  245. 


Rubber  plaster  bow 


bowl  consist  in  its  firmness  and  smooth  surface,  there  being  less  resist- 
ance to  the  spatula  when  stirring.  Its  great  disadvantage  is  in  the 
adhesion  of  the  material  to  the  porcelain,  and  the  difficulty  in  its  removal 
when  allowed  to  harden  in  the  bowl.     The  rubber  bowl  is  flexible,  but 


TMPEESSION  TRAYS. 


287 


is  not  as  agreeable  to  the  operator  in  handling.  Its  surface  not  being 
smooth,  more  resistance  is  offered  to  the  movement  of  the  spatula.  The 
great .  ad  vantage  of  the  rubber  bowl  over  the  porcelain  is  the  ease  with 
which  the  plaster  can  be  removed  after  it  has  hardened.  It  is  also 
possible  to  squeeze  its  sides  together  and  thus  make  a  spout  for  pouring. 
This,  combined  with  the  fact  that  it  is  unbreakable,  seems  to  have 
brought  it  into  general  use. 

IMPRESSION  TRAYS. 

An  impression  tray  is  the  receptacle  by  means  of  which  the  impres- 
sion material  is  conveyed  to  the  mouth,  and  by  means  of  which  it  is 


Fig.  246. 


Fig.  247. 


Full  upper  impression  tray. 


Full  upper  tray  with  deep  flange  for  use  with 
pla.ster. 


brought  into  relation  with  the  tissues  of  which  the  imprint  is  to  be 
made.     It  also  serves  to  retain  this  material  in  place  until  it  hardens, 


Fig.  248. 


Fig.  249. 


Full  lower  fmpression  tray. 


Tray  for  partial  upper  impressions. 


and  in  some  instances  to  remove  it  from  the  mouth.  When  an  impres- 
sion has  been  broken  in  withdrawing  it,  the  tray  serves  as  an  accurate 
matrix  into  which  these  fragments  may  be  fitted. 


288 


LVPEESSfOXS  OF  THE  MOUTH. 


There  are  two  kinds  of  im|)ression  trays  in  f^jeneral  use.  The  first  is 
the  cast  tray,  which  is  made  of  brittania  metal  or  tin.  The  main  ad- 
vantage of  this  type  is  that  it  can  very  readily  be  bent  and  shaped  to 
fit  the  case.     The  other  style  of  tray  is  that  made  of  German  silver  by 


Tray  for  partial  lower  inij'ressions. 


swaging,  and  this  is  very  strong  and  rigid.     For  typical  mouths,  where 
no  bending  or  shaping  is  required,  this  type  of  tray  is  ideal. 

In  selecting   a  tray  for  an  edentulous  mouth  great  care   should  be 
taken  to  have  it  properly  adjustefl  to  the  case  in  hand.     It  should  be 


Fig.  251. 


Full  upper  tray  with  wax  added  at  the  posterior  edge. 

about  three-sixteenths  (y\)  of  an  inch  larger  in  each  direction  than  the 
mouth  for  which  it  is  to  be  used.  For  an  upper  impression,  in  addition 
to  conforming  the  tray  to  the  case,  a  small  roll  of  yellow  beeswax  should 
be  placed  on  its  posterior  edge,  and  while  this  is  still  soft  it  should  be 
placed  in  the  mouth  and  pressed  up  into  proper  position.     The  wax  will 


CLASSES  OF  I3IPRESSI0NS. 


289 


then  receive  an  impression  of  tlie  parts  posterior  to  those  to  which  the 
denture  will  extend,  and  should  then  be  trimmed  down  to  leave  a 
narrow  rim  of  wax  at  the  posterior  edge  (Fig.  251). 

The  object  of  this  wax  is  to  prevent  the  surplus  of  plaster  from  being 
forced  beyond  the  posterior  edge  of  the  tray  and  thus  nauseating  the 
patient.  With  the  wax  properly  fitted  to  the  tray  equal  pressure  upon 
the  tissue  may  be  obtained  at  the  posterior  surface,  as  at  the  buccal  and 
labial  surfaces.  If  wax  be  not  placed  on  the  tray,  as  described,  an  im- 
perfect impression  is  almost  certain  to  result. 

A  Method  of  Making  a  Special  Tray.— In  very  difficult  cases  it  is 
sometimes  necessary  to  make  a  tray,  as  one  suitable  for  the  case  in  hand 
may  not  be  found.  An  impression  is  taken  in  wax  and  a  cast  produced, 
and  over  the  cast  a  sheet  of  wax  one-eighth  (|-)  of  an  inch  in  thickness  is 
placed.  A  zinc  die  is  then  made,  using  the  enlarged  cast  as  a  model, 
and  a  counter-die,  with  which  a  tray  is  swaged  from  German  silver  of 
about  22G.  A  handle  is  then  soldered  on  with  silver  solder,  and  the 
tray  should  exactly  fit  the  case. 

CLASSES  OF  IMPRESSIONS. 

Cases  of  -which  impressions  have  to  be  taken  for  the  making  of  plate 
dentures  may,  for  purposes  of  simplicity,  be  divided  into  four  groups: 

1.  Simple  edentulous  cases  (upper  and  lower),  in  wdiich  the  jaw  is 
typical  and  regular  in  shape,  such  as  Figs.  252  and  253. 


Fig.  252. 


Fig.  253. 


Cast  of  upper  jaw  of  regular  form. 


Cast  of  upper  jaw,  of  which   impression  is 
easily  takeii. 


2.  Complicated  edentulous  cases  with  jaw  irregular  in  shape,  such  as 
upper  cases  with  high  palatal  vaults,  with  cleft  palates,  or  with  very 
high  maxillary  tuberosities ;  cases  in  which  part  of  the  alveolar  ridge  has 
been  removed;  upper  or  lower  cases  in  which  there  has  been  great  re- 
sorption of  the  alveolar  ridge,  and  w^here  the  muscular  and  fibrous  attach- 
ments have  become  in  consequence  abnormally  prominent  (Figs.  254, 
255). 

19 


290 


IMPRESSIONS  OF  THE  MOUTH. 


3.  Simple  partial  cases  in  which  the  remaining  natural  teeth  are  parallel 
and  stand  in  columns,  and  from  which  the  gum  has  not  receded.    Cases, 


Fig.  254. 


Cast  (if  upper  jaw  witli  large  maxillary  tuber- 
osities. 


Cast  of  upper  jaw  with  median  bony  tumc^r. 


in  short,  in  which  it  is  possible  to  remove  the  impression  from  the  mouth 
upon  the  tray  (Fig.  256). 

4.  Complicated  partial  cases  exhibiting  dovetailerl  approximal  spaces 
where  the  teeth  have  been  lost,  and  cases  in  which  tlie  teeth  themselves 


Fig.   2.5G. 


Cast  of  upper  jaw,  showing  teeth  in  a  column  and  having  parallel  long  axes. 

are  bell  shaped.  These  are  the  most  difficult  cases  of  all,  from  the 
taking  of  the  impression  to  the  insertion  of  the  finished  plate  (Figs. 
257  and  258). 

Taking-  a  Full  Upper  Impression  in  Plaster.^When  the  patient 
is  seated  in  the  dental  chair  for  taking  an  upper  impression  the 
chin  should  be  on  a  level  with  the  operator's  elbow  when  the  latter's 
arm  is  dropped  at  the  side  (Fig.  259).  This  gives  full  control  over  the 
field  of  operation  and  is  the  most  convenient  position  for  the  various 
manipulations.  A  towel  or  bib  made  for  the  purpose  is  placed  over  the 
front  of  the  patient's  clothes  to  prevent  injury  from  the  plaster. 

For  an  upper  impression  the  plaster  should  be  placed  higher  on  the 


CLASSES  OF  IMPEESSIONS. 


291 


anterior  third  of  tlie  tray  (Fig.  260)  and  slope  back  to  the  posterior 
edge  of  the  tray.    With  the  left  arm  around  the  patient's  head,  the  index- 


FiG.  257. 


Fig.  258. 


Cast  of  lower  jaw  with  isolated  teeth  not  Cast  of  upper  jaw  exhibiting  several  inter- 

parallel,  dental  undercuts. 


finger  is  placed  in  the  left  angle  of  the  mouth.     The  right  distal  corner 

Fig.  259. 


Proper  relative  positions  of  patient  and  operator  for  taking  upper  impressions. 

of  the  impression  tray  is  introduced  into  the  right  angle  of  the  mouth 
(Fig.  261),  and  then  by  a  rotary  motion  the  left  distal  corner  is  carried 


292 


IMPRESSIONS  OF  THE  MOUTH. 


into  the  left  angle,  and  the  tray  brought  in  so  the  handle  occui)ies  the 
median  line.  Then,  holding  uj)  the  lip  so  that  the  alveolar  border  is 
visible,  the  tray  is  pressed  up  so  that  the  plaster  will  touch  the  anterior 


Fir..  LljlJ. 


Full  n))pLT  tray  with  c  'rirct  anion  nt  uf  plasti-r  fur  taking  an  ini]ii-(_-^ioii. 

portion  of  the  alveolar  l)order  first.     Pressure  is  continued  until  the 
entire  alveolar  ridge  has  been  covered  with  j)laster  and  the  air  has  been 


f  inscrtiiiR  the  tray  in  taking  an  npper  impression. 


forced"  out  at  the  rear,  the  plaster  beginning  to  show  over  the  posterior 
edge  of  the  tray.  Then,  with  the  posterior  edge  of  the  tray  held  firmly 
up  against  the  tissues,  the  anterior  part  of  the  tray  is  pressed  up  into 


CLASSES  OF  IMPRESSIONS. 


293 


proper  position  witli  a  slight  oscillating  motion,  and  the  surplus  plaster 
will  be  forced  over  its  anterior  and  buccal  edges.  The  cheeks  and  lips 
are  then  manipulated  in  such  a  manner  that  the  plaster  will  be  pressed 
well  up  on  the  buccal  and  labial  sides  of  the  aheolar  process.  The 
tray  is  then  to  be  held  firmly  in  position  by  pressure  with  the  fingers 
upon  its  centre  until  the  plaster  sets  (Fig.  262).  While  the  plaster 
is  in  process  of  hardening  the  patient  is  instructed  to  lean  the  head 
forward,  and,  should  signs  of  nausea  be  manifested,  the  request  is  made 
to  breathe  hard  through  the  nose  and  to  hold  the  tongue  down  quietly. 


Fig.   262. 


Correct  method  of  holding  an  upper  impression  tray  in  place  during  the  setting  of  the  plaster. 


If  these  suggestions  are  given  to  the  patient,  ordinarily  there  will  be 
little  trouble  on  the  score  of  nausea. 

After  the  impression  has  been  properly  hardened,  if  it  cannot  be  easily 
removed  by  slight  pressufe  upward  on  the  handle  of  the  tray,  the  finger 
is  passed  up  under  the  lip  to  admit  air  over  the  edge  of  the  impression, 
and  in  this  way  the  adhesion  is  broken  up  and  the  impression  can  ordi- 
narily be  removed  with  ease.  If,  however,  it  should  have  been  left  in 
too  long  and  found  difficult  to  remove,  then  by  the  use  of  a  water  syringe, 
placing  the  nozzle  over  the  edge  of  the  plaster  impression  and  injecting 
a  small  quantity  of  water  on  both  sides  of  the  mouth,  the  impression 
may  be  removed  without  further  difficulty.  A  good  impression  should 
appear  as  in  Fig.  263. 


294 


IMPRESSIONS  OF  THE  MOUTH 


An  accurate  impression  is  absolutely  essential  to  obtain  satisfactory 
adhesion  in  the  phite  denture. 


Fi<!.  263. 


Full  upper  impression. 


Full  Lower  Impressions.— The  i)osition  of  the  patient  for  takint.'  a 
lower  impres.sion  is  sligJitly  different  from  that  required  for  an  upper. 


Fig.  264. 


Relative  positions  of  patient  and  operator  for  taking  lower  impressions. 

The  patient's  chin  should  be  as  high  as  the  operator's  shoulder  (Fig.  264), 
in  order  that  the  tray  may  be  inserted  with  ease  and  that  the  operator 
may  see  clearly  all  parts  of  the  field  of  operation. 


CLASSES  OF  IMPRESSTONS. 


295 


The  selection  of  tlie  tray  is,  as  has  been  previously  stated,  an  import- 
ant part  of  the  operation.  It  must  be  selected  for  and  fitted  to  the  case. 
By  "fitting  trays"  is  here  meant  by  mechanical  means  as  well  as  by  wax 
additions.  After  this  is  properly  adjusted  the  plaster  must  be  mixed 
thick  enough  to  remain  on  the  tray  while  it  is  being  conveyed  to  the 
mouth.  Sufficient  plaster  should  be  placed  on  a  lower  tra>-  to  enable  the 
operator  to  press  the  soft  tissues  out  of  the  way  and  still  have  plaster 
left  to  secure  a  perfect  impression. 

Standing  in  front  of  the  patient,  the  thumb  of  the  left  hand  presses 
back  the  right  angle  of  the  patient's  mouth.  The  left  side  of  the  tray 
is  carried  well  back  into  the  mouth,  and  with  a  rotary  motion  the  right 
side  of   the  tray  is  carried   to  its  place  (Fig.-  265).      The  lower  ho 


Fig.  265. 


Method  of  inserting  the  tray  in  taking  lower  impressions. 

should  be  pulled  down  to  enable  the  operator  to  view  the  alveolar  border, 
and  with  an  oscillating  motion  (Fig.  266),  produced  by  placing  the  index- 
fingers  on  the  tray,  with  the  thumbs  under  the  chin,  the  tray  is  forced 
down  into  .the  desired  position.  The  tray  must  then  be  held  firmly  in 
position  until  the  plaster  is  sufficiently  hardened  to  allow  it  to  be  safely 
removed  (Figs.  267,  268). 

In  edentulous  lower  cases  the  jaw  often  exhibits  at  various  places 
areas  of  hard  and  soft  tissues.  In  such  instances  after  the  tray  is 
fitted,  an  impression  is  taken  either  in  wax  or  in  modelling  compound: 
this  is  removed  and  slightly  enlarged  and  thus  a  perfectly  fitting  tray 


296 


IMI'IiESSIONS  OF  THE  MOUTH. 

Fio.  266. 


Operator  iioldiug  down  lower  lip  mid  bringing  the  plaster  in  contact  with  alveolar  ridge. 

Fig.  267. 


Holding  lower  impression  tray  in  place  during  setting  of  plaster. 


CLASSES  OF  IMPRESSIONS. 


297 


is  secured.     A  thin  coat  of  impression  j)Iaster  is  then  placed  over  its 
surface,  the  tray  returned  to  the  mouth,  and  pressed  into  position.     By 
this  means  an  impression  of  excellent  quality  is  obtained  (Fig.  270). 
The  adhesion  of  the  lower  plate  may  he  greatly  increased  by  extending 


Fig.  26S. 


Full  lower  impression. 


the  lateral  flanges  to  press  upon  the  muscles  of  either  side,  thus  increasing 
the  possibility  of  its  adhesion  and  adding  firmness  to  the  fixture. 

Taking  Partial  Impressions  in  Plaster. — Partial  trays  differ  in  shape 
from  those  used  tor  edentulous  cases,  as  they  are  deeper  and  are  designed 
to  fit  over  the  natural  teeth.     Each  tray  must,  of  course,  be  carefully 


Fig. 

270. 

^^V!&P^^ 

S 

11 

^m£''M(^ 

^ 

t'"^^ 

r   J^tb 

^^^^^ 

p      ■ 

L     wf 

1^  Jj 

H 

^mII 

Cast  of  lower  jaw  with  good  alveolar  ridge. 


Cast  of  lower  jaw  -with  great  resorption  of  the 
alveolar  ridge. 


fitted  to  the  mouth  before  the  impression  is  attempted.  This  should 
be  done  even  at  the  risk  of  mutilating  the  tray  and  destroying  its  future 
value.  The  tray  and  plaster  must  be  regarded  as  simply  a  means  to 
secure  a  perfect  cast,  and  should  be  treated  as  such,  and  there  should  be 
no  hesitation  in  mutilating  a  tray  by  cutting  or  bending  it  to  fit  the  indi- 
vidual case.    When  fitted  the  tray  should  be  three-sixteenths  (y\)  of  an 


298 


IMPRESSIONS  OF  THE  MOUTH. 


iiicli  lar<i;(T  in  each  direction  tlian  tlie  jaw  containin*;;  tlie  natural  teeth,  to 
give  sufficient  bulk  of  plaster  to  enable  the  oi)erator  later  to  replace  the 
broken  pieces  i)roi)erly  in  position  in  the  tray. 

In  takino;  a  i)artial  u])per  impression,  the  position  of  the  ])atient  is  the 
same  as  heretofore  (lescril)e(l  for  an  edentulous  case.  The  tray  having 
been  coated  with  vaseline,  to  insure  its  sei)aration  from  the  plaster, 
and  filled  with  plaster,  is  inserted  into  the  mouth,  as  has  been  already 
described  for  an.edentulous  case.     It  is  then  })ressed  uj)  until  the  natural 


Fig.  272. 


Fig.  271. 


/ 


/ 


Double-end  knilV  used  in  removing 
partial  impre.ssions  :  side  view. 


Impression  knife : 
profile  view. 


Small  pliers. 


teeth  come  in  contact  with  its  floor.  The  cheeks  and  lip  are  manii)u- 
lated  so  the  plaster  will  be  forced  well  up  on  the  buccal  and  labial  sur- 
faces of  the  teeth  and  alveolar  process,  aiul  then  the  tray  is  held  firmly 
in  position  until  hardening  of  the  plaster  has  taken  i)lace.  The  tray 
can  usually  be  easily  detached  from  the  plaster,  which,  of  course,  is  left 
in  the  mouth.  The  plaster  has  now  to  be  removed,  and  this  can  be 
accomplished  best  by  dividing  it  into  sections.  The  knife  shown  in 
Figs.  271  and  272  will  be  found  a  useful  adjunct  to  this  operation. 


CLASSES  OF  IMPRESSIONS. 


299 


With  this  knife  a  groove  is  cut  in  the  pUister  over  the  incisive  e(ig;es  of 
the  anterior  and  the  masticating  surface  of  the  posterior  teeth,  and  over 
the  alveolar  ridges  in  the  approximal  spaces  where  teeth  are  missing. 
The  knife  is  made  strong,  so  that  the  operator  can,  after  cutting  a  groove 


Fig.  274. 


Partial  lower  impression  removed  from  the  mouth  in  sections. 

in  the  plaster,  pry  with  its  blade  and  thus  cause  the  plaster  to  break  and 
be  easily  removed.  Vertical  incisions  should  be  made  in  the  outer 
wall  to  divide  it  into  several  pieces,  thus  permitting  the  buccal  and 

Fig.  276. 


Partial  lower  cast  obtained  from  impression 
shown  in  Fig.  274. 


Partial  lower  impression  assembled  upon  the 
tray. 


labial  walls  to  be  easily  removed,  and  subsequently  the  lingual  portion 
can  be  taken  out  in  one  piece. 

A  small  pair  of  pliers,  such  as  shown  in  Fig.  273,  will  be  needed  to 
remove  the  small  particles  of  the  impression  from  the  mouth. 


300 


iMi'Ri':ssroNs  of  the  mouth. 


Partial  Lower  Impressions.  'I'he  inethod  of  takiii^^  a  lower  impres- 
sion does  not  dift'er  niatcriallN'  from  that  described  for  an  upper.  The 
tray  is  fitted  to  tlie  mouth  and  \aseHne  used  as  ])efore.  When  the  pUister 
is  mixed  and  placed  in  the  tray  there  should  he  ample  surj)lus.  It  is 
placed  in  ])()sition  as  described  for  an  edentulous  lower,  and  held  firmly 
until  the  plaster  has  sufficiently  hardened.  After  the  tray  is  withdrawn 
a  groove  is  cut  over  the  posterior  teeth,  extending  along  the  alveolar 
border,  and  the  pieces  so  obtained  are  removed. 

For  cases  where  the  six  anterior  teeth  are  in  place  and  in  good  con- 
dition the  operation  of  taking  an  impression  is  one  of  some  difficulty. 
This  type  of  case  is  one  of  rather  common  occurrence,  and  unless  the  tray 
is  properly  fitted  the  difficulties  of  the  case  are  increased.  That  which 
is  most  desired  is  a  correct  impression  of  the  partly  edentulous  jaw,  the 
lingual  surfaces  of  the  anterior  teeth,  and  a  tooth  on  either  side,  which 


Fig.   277. 


Partial  lower  tray  prepared  for  taking  impression  of  cast  with  anterior  teeth  remaining. 

may  eventually  be  used  for  clasping.  A  perfect  impression  of  the  labial 
surfaces  of  the  anterior  teeth  is  not  especially  important,  being  of  no 
value  in  fitting  the  piece.  When  a  tray  similar  to  Fig.  277  is  used,  no 
effort  is  made  to  secure  a  correct  impression  of  the  labial  surfaces  of 
the  anterior  teeth.  If  the  surplus  plaster  is  pressed  over  the  labial 
surfaces  it  should  be  cut  away,  leaving,  however,  the  teeth  designed  for 
future  clasping  intact.  TkAing  the  labial  portion  of  the  impression 
cut  away  gives  the  operator  an  opportunity  to  build  the  plaster  cast  out 
as  far  as  may  be  required  to  give  the  desired  strength.  In  this  way 
the  cast  will  be  many  times  stronger  than  if  secured  in  the  ordinary  way. 

The  upper  tray  should  appear  as  in  Fig.  278.  When  this  tray  has 
been  fitted  and  the  wax  added  it  would  present  the  appearance  shown 
in  Fig.  279. 

In  placing  the  impression  plaster  in  the  mouth,  having  the  labial  sur- 


CLASSES  OF  IMPRESSIOXS. 


301 


face  of  the  tray  removed  enables  the  operator  to  perfectly  see  where  to 
place  the  tray  and  press  it  into  position  until  it  comes  in  close  contact 
with  the  teeth.  When  it  is  ready  to  remove,  by  pressing  down  on  the 
posterior  portion  of  the  upper  tray  the  plaster  on  the  sides  will  break, 
the  impression  remaining  in  the  tray.  In  the  lower,  press  upon  the 
posterior  portion  of  the  tray,  and,  with  the  exception  of  small  pieces  being 
broken  at  the  sides,  the  impression  will  remain  in  the  tray  and  may 
be  easily  removed. 

In  some  cases  it  is  found  extremely  difficidt  to  carry  sufficient  plaster 
on  the  tray  into  the  mouth  to  secure  a  perfect  impression.     Especially 


Fig. 


Fig.  278, 


Partial  upper  tray  prepared  for  upper  case 
with  anterior  teeth  remaining. 


Tray  shown  in  Fig.  278  with  wax  added  to  pre- 
vent plaster  from  being  forced  posteriorly. 


is  this  true  if  there  is  a  high  palatal  arch,  or  in  partial  cases  where  the 
remaining  teeth  have  extrtided  to  a  considerable  extent.  This  class  of 
impressions,  while  diffictdt,  is  made  comparatively  easy  by  first  placing 
as  much  plaster  on  the  tray  as  can  be  comfortably  inserted.  Then, 
with  the  spatida,  plaster  is  carried  into  the  mouth  and  placed  in  the 
palatal  vault.  Then  the  tray  is  inserted,  and  the  plaster  in  the  tray  will 
unite  with  that  already  placed  in  position  and  a  correct  impression 
should  result. 


CHAPTER    VIII. 

THE   MAKING  OF   PLASTER  CASTS. 
By  a.  DeWitt  Gritman,  D.  I).  S. 

After  a  plaster  impression  has  been  removed  from  the  mouth  it 
must  be  prepared  for  pouring  the  plaster  cast.  If  it  has  been  removed 
intact  upon  the  tray,  as  is  usually  the  case  in  full  upper  and  lower  im- 
pressions, it  is  only  necessary  to  allow  it  to  set  thoroughly  but  not  to 
dry  out  before  it  undergoes  the  several  steps  of  this  preparatory  treat- 
ment. For  reasons  which  will  presently  become  evident,  not  more  than 
half  an  hour  should  elapse  before  this  is  undertaken. 

An  impression  that  has  been  removed  from  the  mouth  in  sections 
should,  as  a  rule,  be  assembled  in  the  tray.  This  aft'ords  an  accurate 
matrix  into  which  the  pieces  may  be  fitted.  The  broken  pieces  should 
have  their  surfaces  carefully  brushed,  to  free  them  from  any  small 
particles  of  plaster  which  may  adhere  to  them.  The  brush  best  suited 
to  this  purpose  is  a  soft  bristle  brush  about  half  an  inch  in  diameter. 
The  camel's  hair  pencils  frequently  employed  for  this  purpose  are  too 
soft  and  will  not  remove  all  the  particles  of  plaster,  and  thus  the  sur- 
faces cannot  be  accurately  fitted  together.  The  tray  upon  which  the 
broken  impression  is  to  be  assembled  should  also  be  perfectly  clean  and 
free  from  particles  of  plaster.  The  assembling  should  be  done  prefer- 
ably within  five  or  ten  minutes  after  the  impression  has  been  removed 
from  the  mouth.  If  the  impression  has  been  allowed  to  dry  a  few  hours 
its  pieces  should  be  moistened,  as  by  so  doing  the  broken  surfaces  may 
be  more  easily  and  perfectly  fitted  together. 

Beginning  with  the  largest  pieces,  as  they  are  more  easily  joined  by 
reason  of  the  greater  area  of  the  fractured  surfaces,  these  are  carefully 
fitted  into  place  in  the  tray.  The  smaller  pieces  can  usually  be  placed 
in  position  later,  although  the  fitting  together  of  the  pieces  may  require 
some  change  in  this  order  of  procedure.  When  the  assembling  has  been 
completed,  the  lines  of  fracture  should  appear  only  as  hair-lines.  Each 
piece  is  to  be  waxed  firmly  to  the  rim  of  the  tray  as  it  is  put  in  place  by 
flowing  melted  yellow  or  adhesive  wax  at  the  joint  between  the  periphery 
of  the  impression  and  the  rim  of  the  tray.  No  substance,  however,  such 
as  wax,  varnish,  or  plaster,  should  be  interposed  between  the  frac- 
tured surfaces,  nor  between  the  plaster  surface  and  that  of  the  tra>'  to 
which  it  fits,  as  accurate  joining  of  the  parts  would  then  be  impossible. 
Nor  should  any  wax  be  allowed  to  flow  upon  the  surface  of  the  impression 
which  is  to  give  form  to  the  cast.  Great  care  also  should  be  taken  to 
have  the  impression  firmly  waxed  to  the  tray,  so  it  will  not  be  displaced 
while  the  plaster  is  being  thrown  out  of  the  impression  at  the  time  the 
cast  is  poured. 

302 


SEPARATING  MEDIA.  303 

Considerable  care  and  accuracy  are  required  to  assemble  the  parts  of 
a  badly  broken  impression,  and  much  patience  is  necessary  to  obtain 
satisfactory  results,  \yhen  it  is  remembered  that  only  by  attention  to 
the  miiuitest  details  of  assembling  can  a  perfect  cast  be  i)roduced,  the 
profitable  employment  of  time  necessary  to  do  this  is  Tnade  manifest. 

SEPARATING  MEDIA. 

Before  pouring  the  cast  it  is  necessary  to  coat  the  surface  of  the 
plaster  impression  with  some  medium  which  will  prevent  the  aflhesion 
of  the  plaster  of  the  cast  to  that  of  the  impression.  This  medium 
must  be  of  such  a  character  as  not  to  obliterate  any  of  the  details 
of  the  surface  of  the  impression  and  yet  permit  its  separation  from  the 
cast.  Soap  has  been  used  as  a  separating  medium  for  this  purpose,  being 
employed  as  a  solution  of  one  ounce  of  Castile  soap  in  a  pint  of  water 
heated  until  the  soap  is  dissolved.  A  lather  made  by  dipping  a  brush 
in  water  and  rubbing  it  upon  a  cake  of  soap  may  also  be  applied  to  the 
impression.  Thin  liquid  silex  is  also  used  as  a  separating  medium. 
Collodion  may  also  be  used.  The  most  satisfactory  method  employed 
at  the  present  time  is  that  of  double  varnishing  the  impression,  using 
shellac  and  sandarac  varnishes.  By  this  method  the  impression  is  first 
varnished  with  a  solution  of  gum  shellac  in  alcohol,  which  serves  to 
stain  the  plaster  by  soaking  into  its  substance  about  a  sixty-fourth  of 
an  inch,  and  establishes  a  line  of  demarcation  between  the  impression 
and  the  cast,  and  thus  reduces  the  danger  of  marring  the  cast  when 
separating.  The  shellac  serves  also  as  a  filler,  infiltrating  the  surface  of 
the  porous  plaster  and  rendering  it  non-absorbent  for  the  sandarac  var- 
nish which  is  to  follow.  It  should  all  sink  into  the  plaster  and  should 
never  be  thick  enough  to  glaze  it.  After  two  or  three  coats  of  shellac 
have  been  placed  on  the  impression,  and  have  thoroughly  dried,  the 
surface  is  treated  to  a  thin  coat  of  sandarac  varnish.  This  serves  to 
glaze  the  surface  of  the  plaster,  which  in  turn  imparts  a  smooth  surface 
to  the  cast.     The  sandarac  is  also  the  separating  medium  proper. 

One  of  the  most  satisfactory  ways  to  use  shellac  and  sandarac  var- 
nishes is  the  method  employed  by  the  author,  and  that  is  to  use  them 
mixed  in  equal  parts  for  the  first  coat  and  to  use  sandarac  alone  for  the 
second  coat.  The  advantage  of  this  method  is  in  the  saving  of  time,  as 
shellac  and  sandarac  when  mixed  in  equal  parts  will  dry  as  quickly 
as  sandarac  alone.  Great  care  should  be  taken  to  have  the  varnishes 
of  the  proper  consistency.  A  very  safe  rule  is  to  have  them  so  thin 
that  when  placed  on  the  impression  the  first  and  second  coats  will  sink 
into  the  plaster,  and  not  until  after  the  third  coat  will  there  be  any 
gloss  on  the  surface  of  the  impression.  Varnish  that  is  too  thick  will 
obliterate  the  fine  lines  of  the  impression  and  give  an  imperfect  cast. 

Two  varnish  bottles  such  as  are  shown  in  Fig.  280  will  be  found  very 
useful  containers  of  the  media.  The  glass  cap  largely  prevents  the 
evaporation  of  the  alcohol,  which  would  result  in  a  thickening  of  the 
varnish.     Bottle  No.  1  should  contain  sandarac  and  shellac  in  equal 


304 


THE  MAKISG   OF  PLASTER   CASTS. 


parts,  while  No.  2  contains  sandarac  alone.  P^ach  should  be  supplied 
with  a  larjje  and  a  small  brush  for  ap])l ying  the  varnish  ( Fig.  281 ).  These 
brushes  should  be  hung,  by  means  of  wire  hooks  inserted  in  their 
shafts,  upon  a  wire  support  stretched  across  the  mouth  of  the  bottle. 
The  suspension  of  the  brushes  prevents  their  bristles  being  bent  out  of 
shape  b\-  the  weight  of  the  brushes  upon  them.  Very  soft  bristle  brushes 
will  be  found  most  satisfactory.  The  large  brush  is  to  be  used  for  eden- 
tulous cases  and  for  partial  cases,  except  at  the  j)ortions  exhibiting  the 
impressions  of  teeth.  In  these  cases  the  small  brush  will  be  found  very 
advantageous  to  carry  the  varnish  down  into  the  tooth  impressions. 


Fig.  280. 


a 


r 


Vanilsli  bottle  witli  brushes  iiantjing  mi  wire  support. 


Varuish  hruslies. 


From  five  to  ten  minutes  after  the  impression  has  been  rem()\ed  from 
the  mouth  it  may  be  varnished,  first  with  No.  1  (shellac  and  sanda- 
rac), and  five  minutes  later  it  will  be  dry  enough  to  varnish  with  No.  2 
(sandarac),  and  in  five  minutes  more  it  will  be  dry  enough  for  the 
next  step. 

Before  pouring  a  plaster  impression  it  should  now  be  thoroughly 
soaked  in  water  for  not  less  than  from  three  to  five  minutes.  The 
objects  of  this  soaking  are  threefold:  first,  it  enables  the  plaster  to  flow 
freely  over  the  surface  of  the  impression,  as  plaster  flows  poorly  over  a 
dry  surface;  second,  the  impression  does  not  absorb  the  water  from  the 
cast,  thus  allowing  the  plaster  to  harden  naturally  and  to  develop  its 
greatest  possible  strength  (a  dry  impression  would  absorb  the  water  from 


POURING   THE  CAST.  305 

the  cast  and  make  it  worthless);  third,  soaking  the  impression  softens  it, 
and  it  can  be  removed  with  greater  ease  and  with  less  danger  of  break- 
ing the  cast. 

Impressions  of  modelling  compound  receive  no  treatment  preparatory 
to  pouring  the  cast,  save  to  be  thoroughly  wetted  and  to  have  the  excess 
of  water  carefully  shaken  out.  Wax  impressions  receive  a  very  thin 
coat  of  sandarac  varnish,  which  glazes  the  surface  and  permits  an  easy 
separation  from  the  cast. 

Plaster  for  Casts. — Casting  plaster  should  be  much  coarser  and 
stronger  than  that  used  for  impressions,  and  should  set  in  about  twenty 
to  twenty-five  minutes.  It  should  be  the  strongest  and  hardest  plaster 
that  it  is  possible  to  obtain. 

The  author  has  been  recently  using  a  plaster  made  by  mixing  a  very 
coarse  builder's  plaster  with  a  finer  grade  of  casting  plaster,  and  the  casts 
obtained  with  it  have  been  exceptionally  hard. 

POURING  THE  CAST. 

The  technic  of  pouring  the  cast  is  the  same,  irrespective  of  the  material 
of  the  impression,  so  one  description  will  suffice  for  all.  After  the 
impression  has  been  made  ready  the  proper  amount  of  water  is  placed 
in  a  plaster  bowl  and  the  casting  plaster  is  sifted  in  slowly,  so  that  each 
particle  becomes  saturated  with  water  and  settles  to  the  bottom  of  the 
bowl.  Nothing  should  be  added  to  the  water  to  hasten  the  setting  of 
the  plaster,  as  this  will  be  at  the  expense  of  hardness  in  the  cast.  The 
proper  amount  having  been  added  to  absorb  the  water,  the  spatula  is 
used  to  cut  through  the  batter  a  few  times  to  make  the  mix  homogeneous. 
If  the  bowl  is  jarred  on  the  table  any  air  bubbles  present  will  rise  to 
the  surface.  It  is  infinitely  better  to  do  no  stirring  at  all  than  to  stir 
too  much. 

The  operation  of  pouring  the  cast  may  be  divided  into  two  stages 
to  correspond  with  the  two  objects  in  view  in  this  procedure.  In  the 
first  the  surface  is  to  be  perfectly  covered  with  the  soft  plaster.  Ac  u- 
racy  in  this  step  will,  of  course,  determine  largely  the  trueness  of  the 
surface  of  the  cast,  as  any  air  confined  next  to  the  impression,  or  any 
water  left  in  the  tooth  depressions,  or  any  failure  to  have  the  surface 
covered  with  plaster  free  of  air  bubbles,  will  result  in  a  corresponding 
defect  in  the  cast.  The  second  stage  is  simply  to  add  enough  plaster 
to  give  the  cast  proper  bulk. 

In  pouring  a  full  upper  or  lower  cast,  plaster  is  placed  in  the  impres- 
sion at  one  distal  corner,  and  should  follow  the  alveolar  border  around 
to  the  opposite  corner.  By  slightly  jarring  the  impression,  as  it  is  held 
in  the  hand,  by  striking  the  latter  upon  the  work-table,  the  plaster 
is  easily  made  to  flow  over  the  surface  of  the  impression  in  a  thin  coat. 
Most  of  the  plaster  is  then  thrown  out  of  the  impression  by  inverting 
the  tray  and  by  jarring  it  slightly,  leaving  only  a  thin  film  co^'e^ing 
the  surface.  INIore  plaster  is  added.  This  is  also  largely  thrown 
from  the  impression.  This  is  repeated  a  few  times  until  all  traces 
20  .  . 


306 


THE  MAKING   OF  PLASTER  CASTS. 


of  air  bubbles  have  been  removed,  and  the  thin  fihn  of  plaster  re- 
maining on  the  impression  is  smooth.  In  an  edentulous  case  the 
plaster  is  now  added  very  carefully  with  the  spatula,  jarring  each  por- 
tion into  place,  until  it  is  at  least  one-half  inch  thick  in  the  thinnest 
place.  A  mass  of  plaster  batter  is  then  placed  upon  a  glass  slab,  and 
the  partly  poured  impression  is  inverted  o\'er  it  and  pressed  down  on  the 
glass  slab  until  the  cast  is  of  the  desired  thickness,  the  size  and  shape  of 
the  cast  being  determined  by  the  purpose  to  which  it  is  to  be  devoted. 
The  bottom  of  the  tray  should  then  be  parallel  to  the  glass,  in  order 
that  the  alveolar  ridge  of  the  cast  may  be  parallel  to  its  base  (Fig.  282). 
The  square  edge  of  the  spatula,  shown  in  Fig.  244,  is  then  used  to  shape 
up  the  cast  for  metal  or  for  vulcanite  work,  as  desired  in  accordance 
with  the  shape  later  to  be  advised  ff)r  these  two  classes  of  work.  A  slab 
3j  by  4  inches  of  thick  window-glass  will  be  found  very  convenient  for 


Fig.  282. 


Lower  impression  poured  and  inverted  on  glass  slab. 

this  work.  When  the  cast  has  hardened,  glass  of  that  thickness  can  be 
bent  by  placing  the  index-finger  in  the  centre  of  the  glass  and  the 
thumb  and  the  middle  finger  on  opposite  edges  of  the  slab.  By  pressing 
down  with  the  finger  and  raising  up  with  the  thumb  the  glass  can  be 
bent  enough  to  break  up  its  adhesion  and  separate  it  from  the  cast. 
The  object  of  the  use  of  glass  for  this  purpose  is  to  give  a  smooth 
glazed  finish  to  that  surface  of  the  plaster  which  in  the  completed  cast 
will  be  denominated  its  "base." 

In  pouring  partial  upper  and  lower  impressions  great  care  must  be 
taken  to  remove  all  of  the  water  and  air  from  the  tooth  impressions. 
This  is  done  by  flowing  the  plaster  carefully  into  the  impressions  of  the 
teeth,  and  then  by  throwing  it  out  by  jarring  the  inverted  impression. 
This  should  be  repeated  until  all  the  air  and  water  have  been  removed, 
leaving  a  thin  film  of  plaster  over  the  entire  surface  of  the  impres- 


POURING   THE  CAST. 


307 


FiQ.  283. 


angmQ 


sion.  Then  plaster  is  added  to  the  depth  of  one-half  of  an  inch,  care 
being  taken  that  no  air  is  confined  in  the  impressions  of  the  teeth.  Steel 
brads,  such  as  are  shown  in  Fig.  283,  are  then  placed  in  the  soft  plaster, 
from  one  to  four  in  the  impression  of  each  tooth,  with  their  points  toward 
the  incisive  and  masticating  surfaces  of  the  teeth.  Then  the  proper 
amount  of  plaster  is  added  and  the  cast  is  inverted  on 
a  glass  slab  and  shaped  up  with  a  spatula,  as  already 
described.  Steel  brads  for  strengthening  the  teeth  in 
partial  cases  are  about  fourteen  or  fifteen  gauge,  and 
about  three-fourths  or  one  inch  in  length.  These  are 
to  be  preferred  to  brass  brads,  as  they  rust  in  the 
plaster  and  its  attachment  to  them  is  very  secure. 

Removing  the  Impression  from  the  Cast. — After  the  plaster  has  hard- 
ened from  twenty  to  thirty  minutes  (depending  upon  the  quality  and 
the  manner  of  mixing  of  the  plaster)  the  glass  slab  is  removed  by  bending 
it  slightly.  The  edges  of  the  tray  are  freed  of  the  overhanging  plaster, 
and  then,  by  tapping  the  handle  of  the  tray  on  its  upper  surface,  this 
may  be  easily  removed  from  the  impression. 

The  next  step  is  to  remove  the  impression  from  the  cast.  If  it  be  an 
edentulous  upper  or  lower  case,  the  operation  is  a  very  simple  one. 

Fig.  284. 


Brads  used  in  reinforc- 
ing partial  casts. 


Tray  removed  from  impression,  and  plaster  of  latter  cut  down  to  shellac  stain. 


First,  the  outer  edge  of  the  plaster  of  the  cast  is  trimmed  down  so  as  to 
expose  the  outer  edge  of  the  impression  all  the  way  round  and  to  release 
all  undercuts.  The  impression  is  then  cut  down  over  the  alveolar  bor- 
der until  the  warning  yellow  stain  made  by  the  shellac  is  reached  (Fig. 
284).  A  vertical  groove  is  cut  at  each  canine  eminence.  By  tapping 
the  impression  ^^ith  the  handle  of  the  knife  gently  over  the  entire  sur- 
face, then  by  placing  the  point  of  the  knife  at  the  edge  of  the  impression 
and  pressing  away  from  the  cast,  the  buccal  and  labial  portions  of  the 


308 


THE  MAKING   OF  PLASTER  CASTS. 


impression  are  removed.  In  a  full  upper  case  the  palatal  portion  can 
be  removed  in  a  single  piece.  In  a  full  lower  case  one  or  more  grooves 
are  cut  on  the  lingual  surface  of  the  impression,  and  that  portion  can 
then  be  easily  removed  in  sections. 

In  partial  cases  greater  care  should  be  taken  in  this  operation,  as  the 
plaster  teeth  are  very  easily  broken.  The  fact  that  the  im])ression  has 
been  fractured  in  removing  it  from  the  mouth  will  be  of  great  assistance 
in  remo\ing  it  from  the  cast.  After  the  tray  has  been  removed,  and 
the  border  of  the  impression  freed  of  the  overlying  plaster  of  the  cast, 
the  plaster  over  the  incisive  edges  and  masticating  surfaces  of  the  teeth 
is  trimmed  away  very  carefully  until  the  shellac  stain  appears  as  an  in- 
dication that  the  teeth  are  near  at  hand.  Then  the  work  should  be 
directed  to  removing  the  plaster  from  about  the  teeth,  so  they  will  not 
be  caught  in  the  large  masses  of  the  impression  and  broken  off  when  the 
latter  are  removed.  The  plaster  should  be  chipped  from  about  them 
until  this  danger  is  completely  avoided.     Especially  about  isolated  teeth 

Fig.   285. 


Plaster  casts  trimmed;  <iii  left,  for  model  for  die;  on  right,  for  vuleaiiite  wijrk. 

should  the  impression  plaster  be  removed  until  they  are  free  down 
to  their  gingival  margins,  before  any  attempt  to  remove  the  larger 
portions  is  made. 

Trimming  the  Cast. — After  the  impression  has  been  removed  from  the 
cast  the  next  step  is  to  mark  the  plan  of  the  plate,  and  then  the  cast  is 
to  be  trimmed  to  proper  shape  for  vulcanite  or  metal  work.  The 
trimming  is  to  give  proper  form  to  what  are  called  the  sides  of  the 
cast.  The  "face,"  or  that  representing  the  tissues,  and  the  base  of  the 
cast  obtained  by  contact  with  the  glass  slab  have  already  been  deter- 
mined. The  sides  are  determined  by  trimming  away  the  surplus  plaster. 
The  use  for  which  the  cast  is  designed  should  be  considered  in  giving 
form  to  its  sides. 

Casts  for  vulcanite  work  are  trimmed  so  they  are  narrower  at  the 
base,  and  the  face  is  trimmed  to  within  one-eighth  of  an  inch  of  the 
plate  outline.  This  is  in  order  that  they  may  be  set  in  the  vulcanite 
flask  without  further  cutting  (Fig.  285). 


POURING   THE  CAST. 


309 


Casts  for  metal  work  are  trimmetl  so  that  they  are  broader  at  the  base 
than  at  the  face,  in  order  that  they  may  be  withdrawn  from  the  mold. 
The  outline  of  the  base  should,  in  the  first  instance,  be  a  reduced  edition 
of  the  outline  of  the  alveolar  ridge;  in  the  latter,  it  is  to  be  an  enlarged 
edition.  The  sides  should  have  a  uniform  slope  all  around  and  be  made 
quite  smooth.  The  trimming  should  be  done  as  soon  as  the  cast  has 
been  freed  of  the  impression,  as  the  plaster  may  then  be  cut  more  easily 

Fig.  286. 


Plaster  knife. 


and  with  less  brittleness  than  when  it  has  dried  out.  If  the  trimming 
is  deferred  until  this  d^^^ng  out  has  occurred,  it  may  be  better  to  first 
wet  the  cast,  though  it  must  be  remembered  that  this  unfits  it  for  use 
until  it  has  dried  out  again.  It  is  generally  considered  better,  how- 
ever, to  trim  the  cast  without  wetting,  in  which  instance  a  coarse  flat 
double-sided  rasp  will  be  of  great  service  in  shaping  up  the  cast  for 
use.  The  knife  shown  in  Fig.  286  will  be  found  a  very  useful  pattern 
for  this  work. 


CHAPTER    IX. 

DIES,  COUNTER-DIES  AND  MOLDING. 
By  William  H,  Trup:man,  D.D.S. 

The  dies  and  counter-dies  used  in  a  dental  work-room  are  reproduc- 
tions in  metal  of  that  portion  of  a  cast  of  the  mouth  over  which  it  is  de- 
sired to  adapt  by  the  process  of  swaging,  a  sheet  metal  plate  or  appliance. 
These  dies  and  counter-dies  differ  from  those  used  in  the  industrial  arts 
for  a  like  purpose  in  that  they  serve  a  temporary  purpose  only.  As  they 
are  not  designed  to  produce  a  large  number  of  duplicates,  they  do  not 
require  to  be  made  of  a  wear  resisting  metal.  They  are  not  required  to 
produce  upon  the  surface  of  the  sheet  metal  a  sharply  defined  embossed 
design  calling  for  accurate  adaptation  of  the  die  to  the  counter-die.  All 
that  is  required  is  an  accurate  adaptation  of  the  sheet  metal  to  the  sur- 
face of  the  cast,  and  as  this  surface  is  a  series  of  easy  curves  and  rounded 
elevations  and  depressions,  the  force  of  repeated  well  directed  ham- 
mer blows  is  quite  sufficient  to  accomplish  the  swaging.  This  being  the 
case,  the  size  and  shape  of  the  bodies  of  these  dies  and  counter-dies  is 
not  restricted  by  the  mechanism  of  a  stamping  press,  and  their  construc- 
tion is  thereby  very  much  simplified.  If  that  part  of  the  die,  techni- 
cally termed  its  face,  is  an  accurate  duplicate  of  the  corresponding  por- 
tion of  the  model,  and  the  die  is  sufficiently  rigid,  and  is  convenient  to 
handle,  its  size  and  shape  in  other  respects  is  immaterial.  The  dies  are 
made  directly  from  the  model  by  a  process  of  open  mold  casting,  and 
are  usually  made  of  zinc.  The  counter-dies  are  made  by  casting  over 
the  die  a  softer  metal,  and  one  with  a  lower  fusing  point  to  avoid  any 
risk  of  union  of  the  two  by  a  partial  fusing  of  the  die.  The  object  of 
using  a  softer  metal  for  the  counter-die  is  that  it  may,  by  a  change  in 
form  during  the  swaging,  become  slightly  larger  than  the  die,  and  so 
accommodate  itself  to  the  thickness  of  the  sheet  metal.  If  the  die  and 
counter-die  exactly  fit,  and  are  made  of  unyielding  metals,  they  become 
a  punch  and  matrix,  and  cut  and  tear  the  sheet  metal  instead  of  forming 
it  into  the  desired  shape.  The  dies  and  counter-dies  of  the  sheet  metal 
worker's  stamping  press,  to  avoid  this,  are  so  constructed  that  when 
the  press  is  closed  there  is  sufficient  space  between  them  to  accommo- 
date the  metal  used. 

The  process  of  constructing  dies  and  counter-dies  in  the  dental  lab- 
oratory may  be  briefly  stated  as  follows: — 

The  model  is  embedded  in  moldinjj-sand  contained  in  a  tool  termed 
a  molding-flask.  The  model  is  removed,  leaving  a  space  in  the  sand 
known  as  the  mold,  into  which  molten  metal  is  poured,  producing  a 
casting,  the  desired  die.  This  is  now  embedded  in  molding-sand,  only 
leaving  exposed  that  portion  Avhich  is  to  be  included  in  the  counter-die. 

310 


METAL    USED  FOE  DIES  AND   COUNTER-DIES.  311 

A  properly  shaped  metal  ring,  a  casting  or  molding-ring,  is  placed  over 
it  and  molten  metal  poured  in  until  of  sufficient  depth  for  the  counter- 
die.  We  shall  now  consider  in  detail  these  various  steps,  and  the  mate- 
rials and  appliances  used  in  the  process  of  constructing  dental  dies 
and  counter-dies. 

METAL  USED  FOR  DIES  AND  COUNTER-DIES. 

A  metal  suitable  for  denta)  dies  should  possess  the  following  charac- 
teristics : — it  should  be  hard  enough  to  withstand  the  force  of  swaging 
without  marked  bruising  of  its  surface ;  it  should  be  tough  and  not 
brittle,  so  that  it  will  not  break ;  it  should  neither  contract  or  expand 
in  passing  from  its  fusing  temperature  to  that  at  which  it  is  used  ;  finally, 
it  should  be  readily  fusible  in  the  common  heating  appliances  of  a  dental 
laboratory,  and  when  molten  should  possess  a  quick  fluidity,  which  shall 
permit  of  its  flowing  freely  into  small  spaces.  Of  all  the  available  metals 
zinc  possesses  these  several  features  to  the  greatest  degree,  and  is,  there- 
fore in  general  use  for  the  making  of  dental  dies.  jMuch  has  been  said 
and  written  on  the  evil  effects  of  the  contraction  of  zinc  dies.  Dr.  T.  L. 
Buckingham/  by  a  series  of  carefully  conducted  experiments  determined 
that  a  bar  of  zinc  five  inches  in  length  contracted  in  casting  one-eighteenth 
of  an  inch,  or  one-ninetieth  of  its  length.  He  estimated  that  a  die 
two  inches  across  and  two  and  a  half  inches  in  length  on  the  surface 
where  the  plate  is  to  be  made,  contracted  one-forty-fifth  of  an  inch  across 
and  one-thirty-sixth  of  an  inch  in  length.  Such  an  infinitesimal  change 
may  be  wholly  disregarded. 

The  zinc  of  commerce  contains  impurities  varying  greatly  in  amount 
and  in  character  M^iich  somewhat  affect  its  physical  properties  when 
formed  into  dies.  That  sold  as  "the  best,"  costing  a  few  cents  a 
pound  more,  will  generally  prove  satisfactory. 

The  importance  of  properly  caring  for  the  zinc  is  not  generally  ap- 
preciated. To  obtain  the  best  results  the  zinc  should  not  be  overheated. 
If  it  is  allowed  to  become  red-hot,  it  never  works  quite  so  well  after- 
ward. It  oxidizes  rapidly  at  that  temperature,  and  also  alloys  with 
the  iron  of  the  pot.  These  combined  make  it  less  fluid,  it  does  not 
pour  as  well  or  make  so  smooth  a  die.  The  ^'arious  remedies  for  this 
condition  found  in  dental  text-books  have  proved  useless  to  the  writer. 
The  late  Mr.  Joseph  Richards,  an  expert  metallurgist  and  chernist  of 
Philadelphia,  invented  and  patented  a  method  for  improving  oxidized 
zinc,  which  is  used  extensively  and  with  satisfaction.  He  found  that 
the  addition  of  a  very  small  portion  of  aluminum  had  a  very  marked 
deoxidizing  effect  and  quickly  restored  the  zinc  to  its  normal  con- 
dition.^  An  alloy  is  made  of  nine  parts  new  zinc  and  one  part  aluminum. 
To  the  old  and  ozidized  zinc,  while  it  is  in  a  molten  condition,  approx- 
imately one-twenty-fifth  of  its  weight  of  this  alloy  is  added,  and  the 

1  The  Dental  Cosmos,  Vol.  ii.,  p.  144. 

2  The  loss  of  fluidity  in  zinc  when  subjected  to  a  high  temperature  in  melting  is  partly  due  to  its 
alloying  wtth  the  iron  of  the  melting  pot,  a  verj'  small  portion  of  iron  producing  a  marked  effect.  The 
same  loss  of  fluidity  occurs  during  the  process  of  galvanizing  sheet-iron,  in  which  the  sheet  iron  is  dipped 
into  molten  zinc;  after  a  time  the  zinc  looses  its  fluidity.  Mr.  Richard's  method  of  restoring  the  zinc 
to  a  usable  condition  is  largely  used  by  those  engaged  in  this  industry. 


312  DIES,    COUNTER-DIES  AM)   MOLDLXO. 

wliole  thorouijlily  stirred.  Its  effect  is  quickly  noticed,  tlie  zinc  be- 
comes more  Hui(l,  and  the  dirt  and  oxide  separate.  Small  amounts  are 
added,  if  needed,  until  the  zinc  is  in  a  suitable  condition  for  use,  when  it 
may  be  poured  into  ingots,  or  the  separatetl  dross  removed  and  the 
metal  immediately  cast  into  dies.  The  aluminum  acts  as  a  deoxidizing 
agent,  the  amount  needed  is  too  infinitesimal  to  have  any  effect  as  an 
alloy,  and  the  ol)ject  in  first  alloymg  the  aluminum  with  zinc  is  that  it 
may  be  (juickly  disseminated  throughout  the  mass.  Cast-iron  melting 
pots  are  preferable  to  those  made  of  thin  sheet-iron,  as  they  do  not  so 
quickly  become  overheated,  and  are  usually  of  a  more  convenient 
shape.  Before  being  u?ed,  the  inside  of  that  designed  for  the  zinc 
should  be  coated  with  a  paste  of  whiting  and  water,  well  rubbed  in. 
This  should  be  renewed  several  times,  or  until  the  iron  forms  a  protec- 
tive coating  of  its  own  oxide.  Unless  this  precaution  is  taken  the  zinc 
alloys  with  or  eats  into  the  iron,  and  in  a  little  while  makes  a  hole,  usu- 
ally where  the  bottom  of  the  pot  joins  its  sides.  It  is  very  important  to 
keep  one  pot  exclusively  for  the  zinc,  and  another  for  the  lead,  and  to 
have  them  so  plainly  marked  that  the  mistake  of  using  either  for  any 
other  purpose  is  not  likely  to  occur.  They  should  be  frecjuently 
emptied,  and  the  oxide  and  dirt  which  collect  at  the  })ottom,  and  are 
non-conductors  of  heat,  should  be  removed.  When  the  molding-sand  is 
sieved,  and  the  scraps  of  metal  found  therein  returned  to  their  respective 
pots,  any  merely  supposed  to  be  zinc,  or  supposed  to  be  lead,  had  better 
be  discarded. 

Zinc  is  not  a  desirable  addition  to  lead  used  for  counterdies,  while 
zinc  contaminated  with  lead  is  a  very  provoking  mixture  in  a  dental 
laboratory.  A  small  portion  of  zinc  unites  with  lead,  forming  an 
alloy  that  is  no  improvement  over  zinc  for  die  making  ;  the  larger 
proportion  of  the  lead,  however,  remains  as  a  mere  admixture,  and  the 
lead  having  a  lower  fusing  point  and  a  higher  specific  gravity,  remains 
fluid  after  the  zinc  has  set,  and  has  a  tendency  to  settle  to  some  part  of 
the  face  of  the  die.  When  this  takes  place,  if  the  die  remains  in  the 
mold  until  it  has  cooled  below  the  melting  point  of  lead,  the  lead  forms 
a  soft  spot;  if  the  die  is  removed  from  the  mold  at  an  earlier  stage,  the 
still  molten  lead  runs  out  and  leaves  a  vacancy;  in  either  case  the  die 
is  spoiled.  The  method  this  suggests  for  separating  the  two,  i.  e.,  casting 
the  mixed  metals  in  a  cone  shape  mold  and  overturning  it  as  soon  as 
the  zinc  sets,  so  as  to  allow  molten  lead  to  run  out,  and  which  is  recom- 
mended by  metallurgists,  is  very  unsatisfactory  in  dental  laboratory 
practice.  With  ordinary  care  the  metals  used  for  dies  and  counter-dies 
add  so  little  to  the  laboratory  expense  account  that  it  is  economy  to  re- 
new them  when  they  are  found  to  be  in  an  unsatisfactory  state. 

Various  alloys  have  been  recommended  for  tiental  dies  as  preferable 
to  zinc  on  account  of  being  non-shrinking;  perhaps  the  most  note- 
worthy is  a  modification  of  Bab])itt  metal  advocated  by  Dr.  L.  P.  Has- 
kell, of  Chicago,  with  the  following  fornuda: — 

Copper 1  pound 

Antimony 2  pounds 

Tin 8  pounds 


METAL    USED  FOR  DIES  AND   COUNTER-DIES.  318 

Dr.  Haskell  conteiuls  for  this  alloy,  in  addition  to  its  not  shrinking, 
a  decided  advantage  in  its  low  fusing  point.  On  account  of  a  marked 
tendency  of  its  components  to  separate,  he  directs  that  after  it  has  been 
fully  fused,  avoiding,  however,  over-heating,  it  should  be  thoroughly 
and  vigorously  stirred  with  a  wooden  paddle  until  it  is  about  to  set, 
but  still  quite  fluid,  and  then  quickly  poured  into  the  mold.  By  this 
procedure  the  full  advantage  of  the  alloy  is  secured.  If  this  is  not  done, 
the  alloy  quickly  deteriorates  and  produces  rough  and  unsatisfactory 
dies.  For  counter-dies  he  uses  lead  alloyed  with  a  portion  of  tin  to 
reduce  its  fusing  point  and  increase  its  hardness.  It  is  only  with 
great  care  that  lead  alone  can  be  used  for  making  counter-dies  over 
dies  of  this  alloy. 

The  writer,  after  several  years  use  of  this  alloy  for  the  finishing  die  in 
cases  retained  by  a  vacuum-chamber,  abandoned  it,  finding  it  expen- 
sive and  troublesome,  and  of  no  practical  advantage. 

For  small  dies  the  various  fusible  alloys  are  extensively  used,  some 
operators  prefer  to  make  their  working  models  of  these  alloys  instead  of 
plaster,  because  they  are  stronger  and  better  able  to  resist  wear;  or  as 
a  time  saver  where  in  special  cases  the  model  is  wanted  quickly. 
Some  fuse  at  so  low  a  temperature  that  w4th  care  they  may  be  success- 
fully cast  in  modelling  compound  impressions. 

For  counter-dies,  lead  is  generally  used.  The  addition  of  tin  has 
been  recommended  to  increase  the  hardness  of  the  lead.  It  is  of 
doubtful  value.  It  will  generally  be  found  most  satisfactory  to  avoid 
complicating  the,  routine  of  the  workshop  by  adding  materials  seldom 
needed.  In  the  few  cases  where  lead  proves  too  soft  a  metal  for  the 
counter-die,  a  second,  or  a  third  counter-die,  for  the  same  die,  will,  in 
most  cases  overcome  the  difficulty  quickly;  or  in  special  cases  a  counter- 
die  may  be  made  of  zinc,  or  a  low  fusing  alloy. 

A  little  more  than  a  score  of  years  ago  a  peculiar  non-metallic  com- 
pound known  as  Spence's  metal  was  introduced  for  making  dental  dies. 
It  is  non-shrinking,  melts  at  a  low  temperature,  and  is  quite  hard. 
Owing  to  its  being  rather  brittle,  these  dies  will  not  stand  hammer  blows; 
they  can  be  used  only  in  a  press,  and  even  then  require  to  be  protected 
by  iron  boxes,  which  form  part  of  the  press-mechanism. 

Spence's  metal  dies  are  of  use  only  as  finishing  dies  after  the  plate  has 
been  fvdly  swaged  in  the  ordinary  way  with  zinc  and  lead  dies.  The 
fact  that  it  has  only  been  used  to  a  very  limited  extent  may  be  accepted 
as  evidence  that  it  is  not  of  practical  usefulness. 

Lead  having  a  lower  fusing  point  than  zinc,  does  not  oxidize  quite  so 
rapidly,  and  is  not  so  seriously  injured  by  overheating,  nor  is  it  quite 
so  sensitive  to  admixtures.  While  the  accidental  addition  of  a  little 
zinc  is  no  improvement,  it  is  not  a  serious  detriment.  Various  expe- 
dients have  been  recommended  to  prevent  the  lead  oxidizing,  or  to  re- 
duce the  oxide  to  a  metallic  state.  The  writer's  experience  with  them 
has  been  unsatisfactory.  Lead  is  inexpensive,  and  with  care  the  waste 
is  not  a  serious  matter. 


314 


DIES,    COUNTER-DIES  ASD  MOLDING. 


TOOLS   AND   APPLIANCES. 

Where  making  metallic  dies  and  counter-dies  is  a  frequent  operation, 
it  is  a  convenience  to  have  a  bench  especially  designed  for  this  work, 
such  a  one,  for  instance,  as  shown  in  Fig.  287.  The  box-like  upper 
portion  of  this  is  divided  into  two  metal-lined  compartments;  that  at 
the  right  for  the  sand  ready  for  use  (C);  between  the  two  is  located 
a  solid  block  of  wood  upon  which  the  molding  is  done  (A) ;  the  com- 
partment at  the  left  is  covered  by  a  removable  cast-iron  tray,  upon 


Fig.  287 


Molding-bench:  A,  Molding-blofk;  B.  iron  tray;  C,  compartment  for  molding-sand  ready  for  use. 

which  the  molds  are  placed  when  ready  to  receive  the  molten  metal  (B); 
after  the  sand  has  been  used  it  is  passed  into  the  box  beneath  through 
a  square  hole  in  the  tray,  to  remain  until  the  day's  work  is  done,  when 
it  is  sieved  into  compartment  C,  and  damped  so  as  to  be  ready  for  future 
use.  A  drawer  is  provided  for  the  tools,  and  shelves  for  the  metals, 
flasks,  etc.  These  shelves  should  be  covered  with  sheet  zinc.  As  the 
molten  metal  is  liable  to  be  accidentally  spilled  into  the  upper  compart- 
ments, they  should  be  lined  with  copper.  A  wooden  tray  about  two 
feet  square,  with  a  ledge  all  round  about  three  inches  high,  and  lined 
with  copper,  which  may  be,  when  needed,  supplemented  by  an  earthen 
crock  to  hold  the  sand,  makes  a  simple  and  satisfactory  arrangement 
when  space  in  the  work-room  is  limited.  The  tools  used  exclusively  for 
molding  are  few  in  number: — 


TOOLS  AND  APPLIANCES. 


315 


1.  A  Sieve. — This  should  have  about  twelve  meshes  to  the  inch, 
and  to  avoid  rusting,  should  be  made  preferably  of  brass  wire. 

2.  The  Flasks. — These  are  boxes  of  wood  or  iron  in  which  the  mold 
is  made.  If  made  of  wood,  they  may  be  from  four  to  six  inches  square 
and  four  inches  high.  The  wood  should  be  half  an  inch  thick,  and  well 
seasoned.  The  iron  casting-rings  sold  at  the  dental  depots  in  nests  of 
four  or  five  sizes  are  inexpensive  and  make  by  far  the  most  convenient 
molding-flasks.  (Fig.  288.)  Now  and  again  a  model  may  be  encoun- 
tered too  large  for  these,  for  which  a  larger  box  of  wood  may  be  provided. 
These  iron  casting-rings  answer  also  for  making  the  counter-dies.  As 
they  are  liable  to  be  broken  now  and  again,  it  is  best  to  have  a  liberal 
supply,  at  least  four  sets. 

3.  Trowels, — One  or  more  small  trowels,  such  as  are  used  by  iron 
and  brass  founders. 

4.  A  Small  Brush. — To  brush  the  sand  from  the  model  or  the  die  in 
molding  and  making  counter-dies,  a  small  round  paint  brush  or  a 
common  shaving  brush  answers  admirablv. 


Fig.  288 


Set  of  cast-iron  moldinE-rincs. 

5.  A  Wooden  Rule.— This  should  have  straight  edges,  be  from  four 
to  six  inches  long,  and  just  large  enough  to  be  rigid,  say  half  an  inch 
wide  and  one-fourth  inch  thick.  This  is  used  to  level  off  the  sand  in 
making  the  mold,  and  also  to  gently  jar  the  model  before  attempting 
to  remove  it.  The  scraper  shown  in  Fig.  289,  suggested  by  Dr.  A. 
DeWitt  Gritman,  is  a  convenient  tool  for  this  purpose  also. 

6.  A  Glass  Tube.— This  may  be  from  six  to  eight  inches  long,  and  a 
quarter  of  an  inch  in  diameter,  and  is  used  to  blow  out  sand  that  may 
have  fallen  into  the  deeper  portions  of  the  mold. 

7.  A  Point.— A  worn-out  four  or  five-inch  half-round  bench  file  an- 
swers admirably.     The  shank  end,  somew^hat  pointed,  is  used  to  lift 


316 


DIES,   COUNTER-DIES  AND  MOLDING. 


the  model  from  the  mold;  the  other  end  is  often  more  convenient  than 
a  molder's  trowel  in  repairing  molds. 


Fig.  289 


Trowel  and  scraper  use<'ul  in  making  molds. 


8.  An  Iron  Spoon. — The  purpose  of  this  is  to  remove  the  oxide  or 
dross  from  the  surface  of  the  molten  metal,  or  to  remove  it  from  the 
lip  of  the  melting  pot  immediately  before  pouring. 


Fig.  290 


Melting  pots  for  zinc  ami  lead,  with  handle. 

In  addition  to  these,  a  camel's-hair  pencil,  a  small  hammer  or  mal- 
let, a  small  cold  chisel,  and  a  good  hack-saw  are  needed. 


TOOLS  AND  APPLIANCES. 


317 


The  necessary  melting  pots  are  referred  to  elsewliere.  (Chapter  I.) 
The  importance  of  having  separate  pots  for  the  lead  and  the  zinc,  and 
of  having  them  sophiinlj  marked  that  the  one  may  not  be  mistaken  for 
the  other,  cannot  be  too  strongly  enforced.  There  are  many  melting 
pots  on  the  market  lettered  "lead,"  "zinc,"  but  in  letters  so  small  that 
they  are  not  readily  seen  after  the  pots  have  been  some  time  in  use.  A 
marked  difference  in  size  or  shape,  that  can  be  seen  at  a  glance,  is  a  bet- 


FiG.  291 


Fig  292 


Fir,.  29:^ 


LEAD 


ZlNC 


Bailey's  flask. 


Fig.  294 


Fig.  295 


The  Lewis  flask. 


ter  distinction.  (Fig.  290.)  The  pot  containing  zinc  will  need  renew= 
ing  more  frequently  than  that  used  for  the  lead.  After  a  time  the  zinc 
seems  to  alloy  with  the  iron  on  the  inside  where  the  bottom  joins  the 
sides,  and  the  pot  begins  to  leak. 

The  indispensable  tongs  for  handhng  the  melting  pots,  etc.,  is  an  im- 
portant tool.  Those  usually  found  on  the  market  made  of  malleable 
cast-ironarenot  trustworthy.  To  have  the  tongs  break  while  carrying  a 
pot  of  molten  metal  from  the  heating  arrangement  to  the  molding 
bench  is  a  serious  accident.  A  pair  made  to  order  of  wrought  iron  by 
a  blacksmith,  who  is  informed  of  the  use  they  are  to  be  put  to,  will  cost 
but  little  more,  and  will  be  lighter,  more  convenient  to  handle,  and  far 
more  reliable.  They  should  be  from  twenty  to  thirty  inches  long,  of 
which  length  from  three  to  four  inches  may  be  given  to  the  beaks.  ^ 

Among  the  various  special  forms  of  molding  flasks  designed  to  give  a 
definite  shape  to  the  body  of  the  die  may  be  noted  the  Bailey  flask,  in- 
vented by  Dr.  Edward  N.'  Bailey  about  half  a  century  ago.  The  purpose 
of  this  flask  is  to  provide  a  wide  bearing,  extending  beyond  the  face  of 


318 


DIES,    COUNTER-DIES  AND  MOLDING. 


Fig.  296 


Fig.  297 


The  Pearsall  flask 
FiQ.  300 


Lower  half  of  Hawes'  flask 
Fig.  301  Fig.  302 


Hawes'  flask. 


TOOLS  AND  APPLIANCES.  319 

the  (lie  and  resting  upon  the  counter-die,  to  prevent  the  die  tilting  dur- 
ing swaging.  (Figs.  291,  292,  and  293.)  A  later  device,  the  Lewis  flask 
(Figs.  294  and  295),  on  the  contrary,  so  shapes  the  body  of  the  die  that  its 
contact  with  the  counter-die  is  limited  to  the  face,  so  that  all  the  force 
applied  in  swaging  is  expended  in  forcing  the  die  into  the  counter-die. 
A  still  later  device,  by  ^Ir.  W.  Booth  Pearsall,  F.R.C.S.I.,  is  a  rather 
more  complicated  arrangement  to  accomplish  the  same  purposes. 
(Figs.  29G,  297,  298,  and  299.)  The  practical  usefulness  of  these  devices 
is  very  questionable. 

The  Hawes  sectional  molding-flask,  invented  by  George  E.  Hawes, 
of  New  York  City,  to  facilitate  making  dies  for  cases  with  marked  over- 
hanging alveolar  border,  although  complicated,  is  a  practical  device. 
(Figs.  300,  301,  and  302.)  To  one  who  is  expert  in  its  use  it  affords  op- 
portunity of  securing  an  accurate  mold  in  these  difficult  cases  more 
quickly  than  by  the  use  of  cores.  It  requires,  however,  careful  manip- 
ulation to  attain  success. 

MOLDING-SAND. 

A  sand  for  this  purpose  should  be  fine-grained  enough  to  give  a 
smooth  surface  to  metals  poured  over  it,  and  yet  possess  sufficient  poros- 
ity when  packed  in  a  molding-ring  to  permit  the  escape  of  steam 
formed  when  molten  metal  is  poured  into  a  moist  mold, -and  should 
form  a  mass  of  sufficient  coherence  to  maintain  a  given  form  and  to 
permit  the  withdrawal  of  a  properly  shaped  model  from  it  without 
fracture. 

Several  varieties  of  sand  are  used  in  the  dental  laboratory  for  making 
molds.  The  first  and  oldest  is  the  finest  grade  of  iron-founder's  black 
sand;  the  second,  the  brass-founder's  brown  sand;  and  third,  marble 
dust,  or  marble  flour,  made  by  manufacturers  of  fine  plaster  for  building 
and  art  purposes.  The  last  has,  of  late  years,  to  a  great  extent  supplanted 
ihe  others.  While  it  is  no  better,  and  in  some  respects  perhaps  not  as 
good,  it  has  the  merit  of  being  more  cleanly.  Within  a  few  years,  sev- 
eral substitutes  for  molding-sand  have  been  offered  by  the  dental 
supply  houses,  which  are  claimed  to  be  superior  to  it  in  cohesiveness, 
more  cleanly,  to  make  a  smoother  and  sharper  mold,  and  not  to  re- 
quire moistening  before  use.  The  origin  and  composition  of  these  are 
trade  secrets.  While  a  little  more  costlv  than  molding-sand  or  marble 
dust,  in  some  localities  they  may  be  more  readily  obtained,  and  it  can  be 
said  of  them  that  they  answer  the  purpose  very  well. 

Preparing  the  Sand. — Upon  the  preparation  of  the  molding-sand 
will  depend  much  of  the  success  of  die-making.  The  sand  should  be 
moistened  uniformly  and  sufficiently  to  give  a  sharp  line  of  fracture 
when  a  mass  made  by  squeezing  in  the  hand  is  broken,  and  yet  be  in 
such  a  condition  that  it  will  readily  pass  through  the  meshes  of  a  fine 
flour  sieve.  By  far  the  best  plan  to  obtain  this  condition  is  to  moisten 
it,  pass  it  through  a  sieve,  and  let  it  remain  well  packed  in  a  covered 
box  over  night.     When  so  treated  it  acquires  a  certain  "mellowness,' ' 


320  DIES,   COUNTER-DIES  AND  MOLDING. 

anil  greater  {'olicsiveiiess,  makes  a  sniootlier  mold,  and  is  less  liable  tC 
cause  bubbling  when  the  hot  metal  is  poured  over  it.  If  it  is  dry,  and 
re(juired  for  immediate  use,  it  should  be  sifted  so  as  to  break  up  any 
hard  lumps  and  to  remove  any  fragments  of  metal  or  other  foreign  sub- 
stances. Then  water  is  added,  a  little  at  a  time,  thoroughly  diffusing 
each  portion  throughout  the  mass  before  adding  the  next;  when  it  seems 
to  have  nearly,  but  not  quite  enough,  it  is  again  passed  through  the  sieve. 
If  it  is  not  sufficiently  cohesive,  add  a  little  more  water  and  repeat  the 
process.  Thoroughly  working  the  mass  by  rubbing  it  between  the 
hands  or  working  it  over  with  a  trowel  and  sieving  it,  imparts  the  de- 
sired cohesiveness  with  much  less  water  than  if  this  is  not  thoroughly 
done.  If  made  too  moist,  the  casting  will  be  spoiled  by  })ubbling,  that 
is,  owing  to  the  large  amount  of  moisture  present  more  steam  is  genera- 
ted wdien  the  hot  metal  is  poured  over  it  than  can  escape  through  the 
sand,  it  therefore  escapes  through  the  metal  in  bubbles  until  the  metal 
hardens  sufficient  to  prevent  this,  then  the  steam  raises  the  metal  from 
the  surface  of  the  mold  and  makes  an  inaccurate  cast. 

There  is  an  indescribable  feel  to  properly  prepared  molding-sand 
when  a  mass  is  squeezed  in  the  hand,  with  which  the  experienced  molder 
becomes  familiar. 

It  has  been  recommended  to  substitute  oil  for  water  in  the  prep- 
artion  of  molding-sand,  asthe  sand  so  prepared  is  always  ready  for  use. 
This  single  advantage  does  not  compensate  for  the  dirty  working  of  the 
material  tempered  by  that  medium.  Its  odor  when  heated  by  the  mol- 
ten metal  is  also  objectionable.  Glycerine,  or  glycerine  and  water  is  also 
recommended.  It  is  far  less  objectionable  than  oil,  and  while  sand 
prepared  with  it  can  hardly  be  said  to  be  always  ready  for  immediate 
use,  it  does  not  become  unworkably  dry  so  quickly,  nor  so  thoroughly 
dry  as  when  water  alone  is  used,  and  is  to  that  extent  of  decided  advan- 
tage. 

It  is  best  to  sieve  the  sand  immediately  after  it  has  been  used,  and 
then  to  sprinkle  over  it  enough  water  to  keep  it  in  a  proper  condition,  and 
every  night  before  leaving  the  workroom  to  see  that  it  is  damp  enough  to 
be  in  good  working  condition  the  next  day.  If  it  is  allowed  to  become 
quite  dry  and  the  water  added  just  before  using,  it  is  not  so  cohesive; 
the  very  dry  portions  do  not  take  up  water  readily,  and,  although  there 
may  be  more  water  mixed  with  it  than  should  be,  it  will  be  friable  and 
apt  to  make  a  rough  mold;  with  sand  in  this  condition  a  model  which 
would  leave  the  sand  clean  if  it  was  in  good  order,  will  drag  badly.  On 
this  account  it  is  best  to  keep  the  sand  in  a  water-tight  vessel  cf  earthen- 
ware or  metal  or  metal  lined ,  and  tightly  covered.  In  a  wooden  box  it 
becomes  dry  at  the  edges,  and  with  the  small  quantitiy  usually  found  in 
a  dental  laboratory,  this  impairs  very  much  its  working  properties. 

PREPARING   THE   MODEL. 

Apart  from  the  manipulation  which  a  plaster  cast  of  the  mouth  re- 
quires to  impart  to  it  a  desirable  size  and  shape,  more  or  less  prepara- 
tion is  needed  preparatory  to  the   molding  and  casting  process   for 


PREPAniXG   THE  MODEL.  321 

makino-  a  die.  First,  tlie  outline  of  the  plate  or  appliance  for  the 
construction  of  which  the  die  is  required  and  the  position  of  the 
vacuum-cavity,  clasps,  etc.,  must  be  accurately  traced  on  the  model, 
in  order  to  know  how  much  of  the  surface  of  the  model  should  be 
included  in  the  metallic  die.  The  model  should  be  level,  that  is,  its 
face  and  its  bottom  should  be  quite  parallel;  if  it  is  not,  it  should  be 
made  so  by  adding  to  or  cutting  from  the  bottom.  (Fig.  303.)  This 
is  important.  If  the  model  is  not  level,  the  dies  will  have  the  same 
defect,  and  no  matter  how  accurate  they  may  be  in  other  respects,  it 
will  be  a  difficult  task  to  form  with  them  a  plate  that  will  fit.  During 
the  swaging  process  there  will  be  a  constant  tendency  to. drive  the 
plate  toward  that  portion  of  the  die  lowest  in  the  counter-die, 
resulting  in   a  rock  or  spring  very  difficult  to  correct.  "WTiether  the 

Fig. 303 


Full  upper  cast  prepared  as  model  for  a  die. 


model  is  high  or  shallow,  is  a  matter  of  no  moment,  if  it  has 
sufficient  strength.  Regardless  of  the  size  of  the  plaster  model, 
the  die  can  readily  be  given  sufficient  mass  for  strength  at  the  time  of 
castincr.  As  a  matter  of  neatness  and  convenience,  the  model  should 
not  be  much  larger  than  is  actually  required.  About  one-eighth  to  one- 
quarter  of  an  inch  margin  at  the  posterior  line  of  the  plate  in  full  den- 
tures, and  the  width  of  at  least  one  tooth  in  partial  cases  and  regulating 
appliances,  is  usually  sufficient.  The  sides  should  slope  slightly  so  that 
it  will  readily  leave  the  sand.  Fill  up  all  acute  undercuts  not  needed 
on  the  die  that  may  tend  to  prevent  the  model  freely  leaving  the  sand, 
although  they  may  be  at  points  distant  from  the  face  of  the  model- 
If  they  are  not  essential  parts  of  the  model,  fill  them  up  with  either 
plaster  or  wax;  if  they  are,  enlarge  without  deepening  them,  and  with- 
out encroaching  upon  any  portion  of  the  model  to  be  covered  by  the 
plate,  give  them  a  rounded  form.  A  marked  undercut  due  to  a  over- 
21 


322  DIES,    COUNTER-DIES  AND  MOLDING. 

hanginjj  alveolar  ridge,  or  at  the  lingual  asj)ect  of  lower  cases,  may  often 
be  accurately  reproduced  in  the  die  if  so  rounded  as  to  leave  room  for  a 
larger  body  of  sand.  Again,  where  this  cannot  be  done,  the  undercut 
may  be  sufficiently  reduced  in  depth  by  filling  in  with  wax  to  permit 
an  accurate  mold  to  be  made,  and  the  full  dej)th  of  the  undercut  re- 
stored ui)on  the  die  in  a  few  minutes  with  suitable  cutting  tools  before  the 
counter-die  is  made.  If  the  form  for  a  vacuum-cavity  is  desired  on 
the  die,  this  should  be  built  up  on  the  model  with  bees-wax,  or  bees- 
wax and  paraffin,  the  wax  being  added  drop  by  drop  until  of  sufficient 
mass,  and  then  carved  with  a  wax  knife  to  the  desired  shape  and 
thickness.  (Fig.  303.)  Make  its  surface  smooth,  and  to  conform 
somewhat  to  the  contour  of  the  model;  the  sides  slightly  beveled  so  as  to 
leave  the  sand  freely,  and  when  finished,  make  a  shallow  groove  all 
round  with  a  sharp  point,  accurately  following  the  margin  of  the  wax. 
This  will  facilitate  swaging  the  margin  of  the  vacuum-cavity  to  closely 
fit  the  palatal  surface,  and  so  increase  its  usefulness.  Of  the  many 
methods  from  time  to  time  recommended  for  producing  a  vacuum- 
cavity  form  on  a  metallic  die,  this  is  by  far  the  simplest  and  most 
practical.  With  care  and  practice  the  form  for  the  cavity  can  be  neatly 
and  quickly  carved  in  wax  so  as  to  leave  a  sharp  impression  in  the 
sand  and  has  the  further  advantage,  that  any  change  in  its  form 
found  necessary  during  the  molding  process  is  readily  made,  and  the 
model  itself  is  not  marred  or  })ermanently  injured. 

It  will  frequently  be  found  advisable  to  make  additions  of  wax  to 
prominent  points  of  the  model  to  be  used  for  die  making,  because 
these  may  be  bruised  or  slightly  battered  down  in  the  swaging  process. 
The  points  especially  indicated  are  the  rugtie  in  an  upper  and  the  top  of 
a  thin  alveolar  ridge  in  a  lower  model. 

The  preparation  of  models  for  partial  cases  is  complicated  by  the 
presence  of  plaster  models  of  the  natural  teeth.  In  some  cases  this  is 
not  a  serious  matter,  in  others  it  is  quite  so.  In  all  but  notably  un- 
favorable cases  it  is  well  to  first  make  a  trial  mold.  Skillfid  manipu- 
lation learned  only  by  care  and  constant  practice,  enables  an  expert  to 
overcome  many  difficulties;  there  is  an  art  in  molding  and  casting 
which  it  is  well  worth  a  dental  mechanic's  efforts  to  acquire. 

If  the  teeth  lean,  or  are  so  shaped  that  the  model  cannot  be  with- 
drawn from  the  sand  without  displacing  it  so  as  to  impair  the  accuracy 
of  the  mold,  endeavor  to  correct  this  by  so  changing  the  shape  of  the 
teeth  or  the  spaces  between  them  by  adding  wax,  that  a  satisfactory 
mold  can  be  made.  Judgment  is  needed  to  rightly  place  the  wax,  and 
care  to  trim  it  neatly  and  smoothly.  The  wax  may  be  added  a  little 
at  a  time  at  such  places  as  it  is  seen  to  be  needed ;  it  is  better  to  do  so 
than  to  add  an  unnecessary  amount  at  the  beginning.  A  very  little 
will  often  accomplish  the  purpose,  and  not  unfrequently  the  addi- 
tion does  not  materially  encroach  upon  the  face  of  the  die;  where 
it  does,  however,  correction  should  be  made  on  the  die  by  means 
of  files  and  gravers  before  the  counter-die  is  made.  In  extreme  cases 
it  may  be  permissible  to  break  oft'  the  offending  tooth  or  teeth,  but 


MAKING   THE  MOLD.  323 

a  careful  workman  will  avoid  this  wherever  possible.  Mutilating 
the  model  to  facilitate  one  operation  too  often  invites  a  more  serious 
coni])lication  later  on.  Now  and  again  cases  are  met  with  where 
it  is  ad\isable  to  take  a  plaster  impression  of  that  portion  of  the  model 
essential  in  the  die,  and  from  this  make  a  new  model  from  which  the 
dies  are  made.  It  is  well  to  bear  in  mind  that  any  portion  of  a  model 
broken  off,  especially  a  portion  representing  a  natural  tooth,  can 
seldom  be  accurately  replaced.  INlinute  portions  may  crumble  from 
the  fractured  surfaces,  or  foreign  matter  adhere  to  them,  or  the  cement 
prevent  close  contact. 

As  a  final  preparation  for  the  molding  the  model  should  receive  a 
coat  of  thin  quick-drying  spirit   varnish.     Sandarac  varnish  is  gen- 

FiG.  304 


Partial  lower  cast  prepared  as  model  fm-  a  die. 

erally  used  for  this  purpose.  An  unvarnished  plaster  model  has  a  rough 
absorbent  surface  to  which  molding-sand  tends  to  cling.  If  it  is  neces- 
sary to  add  to  or  change  the  surface  of  the  wax  additions  during  the 
process  of  molding,  a  coat  of  varnish  should  be  applied  to  the  disturbed 
surface,  and  allowed  to  dry,  before  again  using  the  model.  This  oc- 
casions, how^ever,  but  a  few  moments  delay. 

MAKING  THE  MOLD. 

Place  the  model  on  the  bench  with  the  back  toward  you  and  its 
face  uppermost;  place  over  it  the  flask,  so  that  it  occupies  a  central 
position,  selecting  a  flask  sufficiently  large  to  allow  a  half-inch  thick- 
ness of  sand  on  all  sides  of  the  model.  Now  take  up  a  handful  of  sand 
and  sift  it  through  the  fingers  upon  the  model,  making  it  as  fine  as  pos- 
sible by  rubbing  it  between  the  hands  until  the  model  is  entirely  covered ; 
then  with  the  fingers  press  it  down  firmly,  packing  it  especially  well  be- 


324  DIES,   COUNTER-DIES  AND  MOLDING. 

tween  the  sides  of  the  flask  and  the  model.  After  the  model  is  covered 
the  sand  may  be  added  more  rapidly  until  the  flask  is  full.  Press  the 
sand  down  firmly  and  evenly,  but  not  too  solidly.  If  it  is  not  packed 
firmly  enough,  the  mold  will  be  rough,  the  model  inclined  to  "drag", 
that  is,  it  will  not  leave  the  sand  freely,  and  the  sand  is  liable  to  be  dis- 
placed when  the  metal  is  poured  in.  If  it  is  packed  too  solidly,  the 
vapor  caused  by  the  hot  metal  will  not  be  able  to  escape  through  the 
sand,  and  there  is  danger  of  the  die  being  injured  by  its  bubbling  through 
the  metal.  The  desirable  mean  between  these  two  extremes  can  only 
be   learned   by   experience. 

AVlien  the  flask  is  full,  level  off  the  surface  with  the  wooden  rule  pre- 
viously mentioned,  or  with  a  suitably  shaped  trowel,  and,  lifting  the 
flask  with  its  contents,  brush  away  the  sand  from  that  part  of  the  bench, 
and  turning  the  flask  over,  carefully  lay  it  down  with  the  bottom  of  the 
model  up.  Next  run  the  point,  held  at  an  angle  of  about  4.0°,  all  round 
the  model,  so  as  to  make  a  bevel  in  the  sand  one-fourth  of  an  inch  deep 
and  from  one-fourth  to  one-half  of  an  inch  wide.  Brush  off  the  sand  the 
point  has  loosened,  or  the  flask  may  be  raised  and  the  sand  thrown  off 
by  a  quick  motion,  care  being  taken  that  the  model  is  not  disturl^ed. 
Now  with  the  fingers  press  the  sand  firmly  all  around  the  model,  and 
see  that  there  are  no  loose  particles  to  fall  mto  the  mold  as  the  model  is 
removed.  Then  take  the  point  in  the  left  hand,  and  resting  the  wrist 
firmly,  place  the  point  about  the  centre  of  the  model,  and  with  a  small 
hammer  gently  tap  it  so  that  it  will  be  driven  slightly  into  the  model, 
and  thus  make  a  handle  with  which  to  lift  it  from  the  sand.  It  need 
enter  but  very  Uttle  to  hold  firmly  enough  for  this  purpose.  Now  care- 
fully raise  the  model  a  very  Httle,  at  the  same  time  gently  tapping  the 
end  of  the  point;  if  it  does  not  readily  leave  the  sand,  let  it  fall  back,  and 
endeavor  to  humor  it  as  it  is  slowly  raised,  so  that  it  will  leave  the  sand 
in  the  direction  of  least  resistance.  These  manipulations  must  be 
made  carefully  and  gently,  or  the  model  may  be  tilted  or  rocked  in  the 
sand  and  so  make  a  false  impression.  In  simple  cases,  if  the  flask  is 
held  with  the  model  downward  and  gentle  tapped,  the  model  will  fall 
out;  in  such  cases  hold  the  flask  over  a  bed  of  sand  that  the  model 
may  not  be  injured  by  the  fall.  In  more  difficult  cases,  especially  those 
for  partial  dentures,  before  attempting  to  remove  the  model,  gently  jar 
it  by  taking  the  wooden  rule,  and,  resting  one  end  of  it  against  the  edge 
of  the  model,  at  the  front,  for  instance,  having  the  other  slightly  raised, 
gently  tap  it  with  a  small  hammer  or  mallet;  repeat  this  at  the  back, 
and  then  at  the  sides;  then  give  the  bottom  of  the  model  a  few  taps 
evenly  distributed.  These  taps  should  be  very  gentle,  they  should  not 
move  the  model:  the  object  is  to  jar  it  so  that  it  will  readily  part  from 
the  sand. 

This  jarring  serves  another  useful  purpose:  the  sand  broken  from 
the  mold  by  an  undercut  or  a  leaning  tooth  may  by  this  jarring  be 
dislodged  and  fall  so  nearly  in  its  proper  place,  that  it  can  be  accurately 
adjusted  in  position  by  the  point,  and  securely  held  by  letting  fall  a  drop 
of  water  on  the  line  of  fracture.     When  this  has  been  done  it  will  not  do 


MAKING   THE  MOLD.  325 

to  invert  the  mold,  any  particles  of  sand  that  may  have  fallen  in  can  be 
removed  by  a  camel's  hair  pencil  moistened  by  hiAng  dipped  in  water; 
when  this  is  touched  to  the  sand, the  sand  will  adhere  to  it.  Extra  care 
will  be  needed  in  pouring  in  the  metal  to  avoid  displac^ing  these  frac- 
tured portions  of  the  mold.  Instead  of  filling  the  mold  at  once,  pour 
in  enough  to  nearly  cover  the  fractured  portion,  then  stop  a  moment  to 
let  the  metal  approach  the  setting-point,  then  add  a  little  more,  just  to 
cover  it,  and  in  a  few  moments  the  operation  may  be  completed.  If 
this  precaution  is  not  observed,  in  all  probability  the  broken  portion 
will  be  floated  from  position  and  the  die  spoiled. 

Having  removed  the  model,  observe  if  any  sand  clings  to  it  on  those 
portions  included  within  the  line  of  the  plate.  If  so,  before  dis- 
turbing it,  examine  the  mold;  if  that  is  not  badly  broken,  proceed 
to  consolidate  the  loose  sand  around  the  edge  of  the  mold  with  the 
fingers,  rounding  the  bevel  made  with  the  point,  and  being  careful 
while  doing  so  that  no  sand  falls  in.  This  accomplished,  the  flask  may  be 
carefully  lifted,  if  it  can  in  that  way  be  more  conveniently  examined. 
First  look  for  any  fractured  portions  that  may  be  restored,  and  make 
them  secure;  then  note  whether  the  sand  brought  out  by  the  model 
seriously  impairs  its  accuracy;  if  it  should  be  at  points  readily  corrected 
in  the  die,  and  the  mold  is  otherwise  satisfactory,  it  may  be  accepted. 
If,  however,  this  is  not  the  case,  an  effort  may  be  made  to  dislodge  the 
sand  from  the  model  without  breaking  it  up  and  adjusting  it  to  place 
in  the  mold.  If  these  expedients  fail,  the  mold  must  be  rejected. 
Before  proceeding  to  a  second  trial,  note  if  any  permissible  changes  in 
the  model  will  overcome  the  difficulty.  It  is  quite  frequent  that  the  first 
effort  fails,  and  yet  suggests  some  little  change  in  the  manipulation  that 
makes  subsequent  efforts  successful  without  any  change  in  the  model. 
A  delicate  sense  of  touch  to  quickly  detect  the  point  where  the  removal 
of  the  model  from  the  mold  is  resisted,  and  judgment  in  overcoming 
the  resistence,  should  be  carefully  cultivated.  In  some  cases,  as  for 
instance,  a  partial  upper  denture  with  a  deep  vault  and  prominent 
rugse,  it  is  necessary  to  press  the  model  forward  and  at  the  same  time  to 
lift  it  from  the  mold  by  raising  the  front  first;  a  similiar  movement 
will  best  serve  for  a  full  lower  denture  with  a  marked  undercut  at 
its  lingual  aspect.  A  full  upper  denture  with  a  marked  overhanging 
in  front,  requires  the  manipulation  to  be  reversed.  At  times  a  broken 
mold  can  be  repaired  by  adding  sand  to  replace  that  broken  away. 

There  are  cases  in  which,  despite  repeated  attempts,  good  molds 
are  not  secured.  One  class  of  these  cases  is  formed  of  those  having  an 
overhanging  alveolar  ridge,  particularly  at  the  frontal  portion.  If  the 
undercut  is  not  too  marked,  the  front  of  the  model  may  be  raised, 
bringing  the  axis  of  this  portion  of  the  ridge  nearer  to  a  vertical  line. 
An  inclined  bed  of  sand  is  made,  the  front  of  the  model  resting  upon 
its  highest  portion,  the  heel  of  the  model  upon  the  floor  of  the  sand 
tray;  it  is  enclosed  by  a  molding-ring  or  flask,  and  the  sand  packed  as  be- 
fore described.  By  this  expedient  the  position  of  the  model  in  the 
mold  favors  its  removal  in  line  with  the  projecting  ridge.     If  the  mold 


326 


DIES,   COUXTER-DIES  AND  MOLDING. 


is  accurate,  it  is  set  on  an  inclined  })e(l  of  sand  so  that  the  line,  C,  D 
is  almost  or  quite  horizontal  as  at  A,  B  (Fiji;.  305),  before  casting  the  die. 
This  may  be  modified  by  placing  the  model  within  the  flask  as  usual, 
and  making  a  chalk  mark  on  the  side  of  the  flask  accurately  in  line 
with  the  projecting  ridge.  When  ready  to  remove  the  model,  place 
the  flask  and  its  contents  upon  an  inclined  bed  of  sand  so  that  the  chalk 
line  is  vertical.  After  this  has  been  accomplished  the  flask  is  restored 
to  the  floor  of  the  molding  bench.  All  the  advantages  of  the  first 
method  are  secured  by  the  second,  with  the  added  advantage  that  the 
mold,  in  its  relation  to  the  flask,  is  more  convenient  for  pouring  the 
metal,  and  the  cast  will  be  level. 

The  undercut  may  be  so  marked  that  this  exj)edient  does  not  suffice. 
The  device  known  as  the  Hawes  flask  is  now  in  order.  This  device 
consists  of  two  sections.     Fig.   300   represents  the  lower  section  of 


Diagram  showing  method  of  tilting  model  to  avoid  undercut 


the  flask,  slightly  open,  to  show  the  joints;  Fig.  301  is  the  upi)er  sec- 
tion. When  ready  for  use  the  lower  section  is  closed  and  confined  by  a 
pin,  and  the  plaster  model  is  placed  in  it,  as  represented  in  Fig.  302. 
Slips  of  thin  but  stiff  paper  are  placed  between  the  jaws  of  the  three 
flanges  projecting  inward  toward  the  model,  cut  to  approximately  fit 
the  sides  of  the  moilel,  and  just  touching  it,  to  part  the  sand  when  open- 
ing the  flask  for  the  removal  of  the  model.  The  model  should  be  ad- 
justed as  to  height  so  that  the  most  prominent  part  of  the  alveolar  ridge 
is  about  level  with  the  upper  edge  of  the  flask.  The  sand  is  now  packed 
into  the  space  between  the  model  and  the  flask  until  it  is  level  with  its 
upper  edge,  and  finished  oft'  to  a  smooth  even  surface.  As  the  mold 
is  to  be  divided  horizontally  at  this  point,  the  level  of  the  sand  should  be 
so  adjusted  that  the  edge  next  to  the  model  is  thick;  this  usually  requires 
that  the  parting  should  be  a  litde  below  the  most  prominent  portion  of 


GORE-MOLDING.  327 

tlie  ridg'e.  Carefully  remove  all  particles  of  loose  sand  from  the  face 
of  the  model  and  the  finished  surface  of  sand.  The  sand  and  face  of 
the  model  must  now  be  covered  with  dry,  pulverized  charcoal,  sifted 
evenly  over  the  whole  surface.  Holders  keep  it  in  a  bag  which  they 
shake  over  the  flask.  When  this  is  done,  the  upper  section  of  the  flask 
is  placed  upon  the  lower,  three  guide  pins  holding  it  securely  in  place 
while  it  is  carefully  filled  with  sand.  It  is  then  raised  from  the  lower 
section  and  laid  aside.  The  long  guide  pin  is  now  withdrawn  and  the 
lower  section  carefully  opened  and  the  model  removed.  The  lower 
section  is  then  closed,  the  pin  replaced,  and  the  upper  section  adjusted, 
and  the  flask  inverted.  It  is  now  ready  to  receive  the  metal.  With 
this  flask  accurate  molds  may  be  made  of  models  having  quite  marked 
projecting  or  overhanging  alveolar  borders;  to  accomplish  this, however, 
some  little  practice  and  great  care  is  required.  The  edges  of  the  sand 
where  the  mold  is  divided  are  very  friable  and  apt  to  be  displaced  in 
opening  and  closing  the  mold.  It  is,  moreover,  useful  in  few  cases  other 
than  full  upper  dentures.  On  this  account  it  is  but  little  used.  A 
more  generally  applicable  method  of  overcoming  such  molding  difficul- 
ties is  by  the  use  of  cores. 

In  most  cases  two  zinc  dies  are  required,  and  two  molds  must  be 
made.  It  not  unfrequently  happens  that  repeated  efforts  must  be 
made  before  satisfactory  molds  are  secured,  and  now  and  again  one 
must  be  satisfied  with  the  best  that  can  be  obtained  and  depend  upon 
correcting  the  defects  of  the  mold  by  carving  the  die  cast  in  it.  It  may 
be  a  question  whether  it  is  best  to  do  this  or  to  spend  a  great  deal, 
more  time  in  the  eflFort  to  secure  a  better  mold  by  the  troublesome 
process  of  making  cores.  After  satisfactory  molds  have  been  made 
they  should  be  laid  aside  where  they  will  not  be  injured  before  the 
metal  is  poured  in.  It  should  be  remembered  that  a  sand  mold  is 
quite  friable,  and  becomes  more  so  if  allowed  to  dry.  It  is,  therefore, 
prudent  to  make  the  casting  as  soon  as  possible. 

In  these  difficult  cases,  as  the  labor  of  pouring  the  metal  in  the  mold 
is  but  trifling,  it  is  well  to  make  several  dies  and  select  the  two  best. 


CORE-MOLDING. 

In  cases  where  it  is  otherwise  impossible  to  obtain  a  sufficiently  accurate 
sand  mold  owing  to  sharp  undercuts,  leaning  teeth,  etc.,  recourse  is 
had  to  core-molding.  Cores  are  temporary  additions  made  to  the 
model  which  so  change  its  shape  at  the  points  where  difficulty  exists 
that  an  accurate  sand-mold  can  be  made.  These  cores  are  in  position 
on  the  model  when  the  sand  mold  is  made;  they  are  then  removed 
and  placed  in  the  prints  they  have  made  and  then  become  part  of  the 
mold.  They  are  made  of  a  quick  hardening  plaster  that  can  be  molded 
to  the  model,  has  sufficient  strength  to  bear  the  necessary  handling, 
and  will  not  interfere  with  the  process  of  casting.  Plaster  of  Paris,  to 
which  has  been  added  about  two-thirds  of  its  bulk  of  either  pulverized 


328  DIES,   COUNTER-DIES  AND  MOLDING. 

pumice  or  soap  stone,  molding-stone,  whiting,  asbestos  flour,  or  any 
similar  substance  that  will  mix  with  the  plaster  and  enal)le  it  to  bear  a 
red  heat  without  cracking  or  shrinking,  is  in  common  use  in  dental 
laboratories.  The  investment  materials  recently  introduced  are  ad- 
mirable for  this  purpose.  In  order  to  avoid  bubbling  '  the  cores  must 
be  thoroughly  dried  or  baked  before  the  molten  metal  is  brought  in 
contact  with  them,  and  as  the  sand  molds  must  be  used  very  soon  after 
they  are  made,  the  core  material  must  admit  of  this  being  done  quickly 
without  change  of  bulk  or  shape.  The  drying  is  conveniently  done 
over  a  gas  flame,  or  by  means  of  the  blow-pipe,  care  being  taken,  how- 
ever, not  to  burn  off  or  destroy  the  sharp  edges.  This  is  usually  done 
after  the  mold  has  been  made,  as  the  baking  make  the  cores  friable 
and  easily  broken,  or  if  this  is  avoided  by  careful  handling,  if  the  cores 
are  long  in  contact  with  the  damp  sand,  they  may  take  from  it  sufficient 
moisture  to  bubble  as  freely  as  though  they  had  not  been  baked. 

^Miatever  is  added  to  the  plaster  used  in  making  cores  must  be  in  a 
fine  powder,  free  from  lumps,  and  must  be  thoroughly  mixed  with  it. 
The  usual  precautions  of  first  preparing  the  model  by  varnishing  or 
oiling,  that  the  material  of  the  core  will  not  unite  with  it,  must  be  ob- 
served. While  cores  must  extend  as  far  as  needed  to  facilitate  molding, 
it  is  desirable  to  keep  them  as  smali  as  is  consistent  with  strength 
and  their  ready  replacement,  and  to  so  shape  them  that  they  will  leave 
in  the  sand  an  impression  that  will  hold  them  accurately  and  securely 
in  place  when  the  metal  is  poured  into  the  mold.  As  these  cores  when 
baked  are  hght  compared  with  the  metal,  unless  securely  held,  they  are 
apt  to  float  out  of  position  when  the  casting  is  made.  To  prevent  this 
the  metal  should  be  poured  in  the  mold  slowly,  a  little  at  a  time,  so 
that  the  first  portion  wdll  have  commenced  to  set  and  assist  in  holding 
the  core  in  place  before  the  mass  of  metal  is  added,  and  yet  this  must 
not  be  done  so  deliberately  that  the  various  portions  do  not  unite  as 
thoroughly  as  though  the  pouring  was  continuous. 

Cores  are  needed  for  models  of  edentulous  upper  jaws  more  frequently 
on  account  of  a  marked  overhanging  ridge.  In  these  cases  it  is  usually 
best,  and  is  usually  practicable,  to  make  one  large  core  to  embrace 
the  front  of  the  model  so  far  as  the  overhang  extends,  as  shown  in  Fig. 
306.  Occasionally,  however,  the  depression  of  each  side  may  be  so 
marked  that  it  is  necessary  to  divide  this  on  the  median  line.  Occa- 
sionally, a  core  may  be  needed  for  a  very  deep  vault,  but  they  are  not, 
however,  very  satisfactory.  A  slight  displacement  of  a  core  from  this 
position  seriously  impairs  the  accuracy  of  the  die,  while  a  like  displace- 
ment in  any  other  position  would  be  of  little  moment.  It  is  generally 
best  to  accept  the  lesser  evil  of  judiciously  adding  wax  to  the  model  until 
a  sand  mold  can  be  made.  The  resulting  inaccuracy  seldom  proves 
a  serious  fault,  as  close  adaptation  of  the  plate  is  not  imperative  in 
this  position,  indeed,  in  some  cases  it  is  not  desirable.    Models  of  the 

i-  When  hot  metal  is  poured  into  a  mold,  any  moisture  present  is  converted  into  steam,  and  this 
escapes  through  the  sand.  The  material  of  which  the  cores  are  made  is  too  dense  to  permit  this;  it 
therefore  bubbles  or  boils  up  through  the  metal,  and  usually  spoils  the  die.  To  avoid  this,  the 
cores  are  thoroughly  baked  at  a  heat  higher  than  that  of  the  molten  metal. 


CORE-MOLDING. 


329 


lower  edentulous  jaws  with  a  marked  inward  lean  of  the  ridge  may 
require    cores    to    secure    accuracy    of   its    lingual    aspect.     In    such 


Fia.  306 


Full  upper  model  with  alveolar  undercut,  showing  form  of  core  to  fill  in  undercut. 

cases  it  is  usualfy  best  to  make  the  core  in  two  sections  shaped  as 
shown  in  Figs.  307  and  308,  so  as  to  permit  of  their  removal  without 


Fig   307 


Full  lower  model  with  lingual  alveolar  undercut,  and  core  in  two  pieces  in  place. 

injury  to  the  model.  The  conditions  calling  for  cores  in  partial  cases  of 
either  jaw  are  so  various  that  only  general  instructions  for  making  them 
can  be  given.     They  should  be  so  arranged  that  they  can  be  readily 


330  DIES,    COUyTER-DIES  AND  MOLDING. 

removed  without  injury  to  the  model;  they  shoukl  be  as  small  as  is  con- 
sistent with  the  correction  of  the  trouble  requiring  their  use  and  their 
secure  adjustment  in  the  mold.  Thin  edges  of  either  the  core  or  the 
sand  niohl  are  to  be  avoided,  and  the  general sliajx'  .should  be  such  that 
they  can  be  accurately  replaced  in  the  mold. 

Now  and  again,  especially  with  models  for  partial  lower  cases  with 
leanintr  teeth,  it  is  expedient  to  let  the  core  take  the  form  of  an  impres- 
sion in  sections.  The  separate  portions  accurately  united  and  held 
together  with  adhesive  wax  applied  on  the  inside,  form  a  mold  to  be 
imbedded  in  a  mass  of  the  same  material  of  which  they  are  made.  This 
is  thoroughly  dried  and  the  metal  poured  in.  For  convenience, 
just  before  pouring  this  mold  may  be  imbedded  in  molding-sand, 
and  a  casting-ring  used  to  give  the  die  a  proper  size  and  shape. 

At  times,  it  is  better  in  such  cases  to  take  a  plaster  impression  of 
the  model  in  sections  from  which  to  make  a  new  model  of  that  portion 

Fig.  .308 


Under  view  of  two-piece  core  for  full  lower  model  .shown  in  Fig.  307. 

to  be  covered  by  the  plate,  and  from  this  to  remove  the  teeth.  This  sim- 
plifies very  much  the  making  of  the  dies.  The  plate  is  made  on  this  new 
model,  the  portion  extending  upon  the  teeth  being  afterward  added  in 
theformof  soldered-on  collars,  made  and  adjusted  to  theoriginal  model. 
In  some  cases  of  marked  leaning  teeth  very  firm  in  position,  exact 
accuracy  is  not  required,  as  an  accurately  fitting  plate  cannot  be  forced 
over  them. 

Theoretically,  cores  offer  a  ready  means  of  obtaining  accurate  dies  of 
difficult  cases.  Practically,  however,  they  are  troublesome,  and  very 
uncertain.  It  is  much  better  if  a  die  sufficiently  accurate  can  be  ob- 
tained without  them,  even  though  the  file  and  graver  must  be  freely  used 
to  correct  the  short-comings  of  the  casting.  The  actual  manipulation  of 
making  cores  differs  in  nowise  from  the  usual  plaster  working  of  the  dental 
laboratory.  The  plaster  should  be  applied  to  the  model  neatly,  and 
be  confined  to  that  portion  requiring  a  core.  When  fully  set,  it  should 
be  removed,  ("arved  to  proper  shape  to  freely  part  from  the  sand  mold 


CASTING   THE  DIES.  331 

and  to  lea\e  an  impression   fa\oring  its  accurate  replacement.     All 
the  outer  surfaces  should  be  made  smooth  and  then  varnished. 


CASTING    THE    DIES. 

AMien  ready  to  begin  casting,  the  molds  are  arranged  on  the  casting 
bench  in  convenient  positions  for  pouring  the  metal.      Suitable  casting- 
rings  should  be   close  at  hand,  together  with  a  supply  of  molding-sand 
with  which  to  close  any  openings  between  the  molds  and   the  casting- 
rings  through  which  the  metal  might  escape.     The  metal  having  been 
fused  in  the  melting  pot,  is  brought  to  the  bench.     With  an  iron  spoon, 
or  some  such  tool,  remove  any  oxide  or  dirt  floating  on  the  surface  of 
the  metal,  especially  from  near  the  lip  of  the  pot.     If  the  metal  is  very 
hot,  it  is  best  to  delay  pouring  until  it  has  somewhat  cooled.     It  is  desir- 
able that  the  metal   shall  quickly  set  when  poured  into  the  mold,  so 
that  its  principal  shrinkage  shall  take  place  in  the  centre  of   the  mass. 
Pour  the  metal  in  a  gentle  stream  into  the  mold  at  one  of  its  back  cor- 
ners, holding  the  lip  of  the  melting  pot  as  close  as  possible  to  the  sand. 
If  the  metal  is  poured  in  from  a  height,  or  in  too  heavy  a  stream,  the 
sand  of  the  mold  is  liable  to  be  disturbed  and  the  die  rendered  thereby 
rough  and  inaccurate;  on  the  other  hand,  the  pouring  must  be  done 
quickly  enough  for  the  metal  to  ficw  into  position  before  being  chilled.^ 
When  the  sand  mold  is  filled,  if  the  die  is  not  thick  enough,  immedi- 
ately place  over  it  a  casting-ring,  the  largest  end  down,  pressing  it  gently 
into  the  sand  so  that  the  metal  will  not  escape  under  it,  and  continue 
the  pouring  until  enough  metal  has  been  added.     A  little  sand  packed 
around  the  outside  of  the  ring  will  quickly  arrest  a  flow  of  metal  under 
it.     If  bubbling  occurs,  stop  pouring  for  a  few  moments  when  the  mold 
is  about  half  full,  and  just  before  the  metal  in  the  mold  begins  to  set, 
pour  in  more  metal,  holding  the  melting  pot  at  a  little  height  over  the 
mold.     If  the  bubbling  has  been  slight  this  will  frequently  save  the 
die;  if,  however,  it  has  been  quite  marked  the  die  is  usually  worthless. 
It  is  time  saved  to  have  the  melting  pot  large  enough  to  hold  sufficient 
metal  for  several  dies,  and  to  pour  several  from  the  one  melting.     When 
the  dies  are  fully  set,  turn  them  out  of  the  mold,  and  examine  their  con- 
dition.     Zinc,   when  quite  hot   is  far  easier  to  work  than  when  cold; 
expert  workmen  take  advantage  of  this  by  cutting  off  the  teeth  of  dies 
for  partial  cases  with  a  pair  of  large  wire  cutters,  or  a  cold  chisel,  or 
hack-saw,  and  with  file  and  gravers  roughly  correct  any  inaccuracies 
that  may  be  noted.     This  can  readily  be  done  while  the  die  is  far  too 
hot   to   handle   by  holding   it   in   the   large   bench    vise,   and    much 

1  Dr.  A.  DeWitt  Gritman,  of  Philadelphia,  suggests  the  following  method  of  casting  zinc  dies:  He 
does  not  empty  the  zinc  pot,  but  keeps  it  at  least  about  one-third  full  at  all  times,  so  that  there  is  alwa>-s 
a  quantity  of  zinc  in  immediate  contact  with  the  walls  of  the  pot.  This  more  promptly  melts  than  would 
a  mass  not  in  contact,  and  the  pot  does  not  become  overheated.  He  begins  to  pour  the  metal  when 
sufficient  is  melted  to  partly  fill  the  mold,  then  returns  the  pot  to  the  fire  until  another  portion  is 
melted;  this  he  pours,  and  continues  to  melt  and  pour  until  the  casting  is  complete.  By  this  pro- 
cedure the  zinc  is  never  overheated,  but  is  poured  at  as  low  a  temperature  as  possible,  and  may  be  used 
for  years  without  deterioration.  He  claims  also  that  there  is  less  shrinkage  on  the  face  of  the  die. 
Care  is  needed  that  the  portion  poured  does  not  chill  before  another  portion  is  added. 


332  DIES,    COUyTEIi-DIEJS  AND  MOLDISU. 

time  and  labor  are  saved.  Wlien  cold,  the  die  is  critically  examined,  and 
any  corrections  needed  before  making  the  counter-die  arc  lunv  made. 
If  for  a  partial  plate,  the  teeth  may  now  be  cut  from  the  least  desirable 
die,  or  this  may  be  deferred  until  after  the  counter-die  has  been  made. 
Any  places  where  wax  has  been  added  to  facilitate  making  the  mold 
should  now  be  corrected  by  cutting  out  the  zinc  to  make  it  conform  to 
the  model.  Inaccuracies  due  to  imperfect  molding  on  that  portion 
of  the  die  to  be  covered  by  the  plate  will  also  need  attention.  Spaces 
between  teeth,  undercuts,  and  the  margin  of  vacuum-cavities,  should  be 
carefully  compared  with  the  model,  and  made  to  correspond  as  nearly 
as  possible.  In  making  these  corrections  the  cold  chisel  may  be  used 
where  much  has  to  be  removed;  as  a  rule,  however,  the  files  and  gravers, 
and  occasionally  a  bur  in  the  dental  engine,  will  prove  effective  tools. 
It  is  just  as  important  not  to  remove  too  much  as  it  is  to  remove  enough, 
and  very  important  not  to  encroach  upon  any  portion  of  the  die  that 
does  not  need  correction.  When  these  corrections  have  been  made, 
casting  the  counter-die  will  be  next  in  order. 


CASTING   THE   COUNTER-DIES. 

in  making  a  counter-die  three  points  are  to  be  considered  regarding 
its  office  during  swaging: — First,  it  is  to  force  the  plate  into  contact 
with  the  die;  second,  to  accomplish  this  it  must  hold  the  die  in  position; 
and  third,  it  must  by  its  shape  and  mass  make  for  the  die  a  solid  foun- 
dation. It  must  take  in  all  the  face  of  the  die  that  is  to  be  covered  by 
the  plate,  and  sufficient  beyond  this  to  prevent  the  die  changing  its 
position.  This  usually  requires  that  it  shall  extend  about  half  an  inch 
over  the  sides  of  the  die.  In  mass,  it  should  be  a  full  half  inch  thick 
over  the  most  prominent  portions  of  the  die.  Convenience  of  handling 
and  an  eye  for  neatness  will  suggest  that  neither  die  nor  counter-die 
should  be  unduly  massive;  they  should,  however,  be  properly  propor- 
tioned to  the  size  of  plate  to  be  swaged,  and  well  able  to  bear  without 
breaking  or  change  of  form,  the  impact  of  a  heavy  hammer. 

The  first  step  in  making  a  counter-die  is  to  place  the  die  in  a  casting- 
ring,  face  up,  elevated  by  packing  sand  beneath  it  until  the  plate  line  is 
about  one-fourth  of  an  inch  above  the  edge  of  the  ring.  In  cases  in  which 
the  plate  is  confined  to  the  face  of  the  die,  as  in  partial  plates,  the  dies 
should  be  from  one-half  to  three-quarters  of  an  inch  above  the  ring.  The 
die  will  extend  into  the  counter-die  just  as  far  as  it  extends  above  the 
ring.  While  it  is  necessary  that  it  should  extend  into  the  counter-die 
sufficiently  far  to  be  firmly  held  in  position,  if  this  is  overdone,  it  will 
prove  embarrasing  in  separating  the  die  and  counter-die  and  in  removing 
the  plate  from  the  counter-die  after  swaging.  After  the  die  is  adjusted 
as  to  height,  see  that  its  face  is  quite  level,  and  then  firmly  pack  molding- 
sand  between  the  die  and  casting-ring,  filling  the  space  solidly.  With  a 
point  or  small  molding-trowel,  smooth  off  this  sand  level  with  the  top  of 
the  ring.     xAfter  carefully  removing  any  sand  that  may  have   fallen  on 


LOW  FUSFNG  ALLOY  DIES  AND  COUNTER-DIES.  333 

the  face  of  the  die,  place  over  it,  large  end  down,  a  casting-ring  just  large 
enough  to  leave  about  one-half  of  an  inch  of  space  all  around  the  die. 

The  die  is  now  ready  for  casting  the  counter-die.  While  there  is  a 
fair  margin  between  the  fusing  temperature  of  lead  and  of  zinc,  thev 
will  unite  if  the  lead  is  poured  too  hot.  If  all  the  lead  in  the  pot  is 
molten,  it  is  safe  to  conclude  that  it  is  too  hot  to  be  safely  poured  over 
the  die.  It  is  best  to  wait  until,  on  tilting  the  melting  pot,  the  metal  is 
seen  to  cling  to  its  sides.  When  this  condition  has  been  reached,  the 
metal  is  poured  into  the  ring  until  it  is  about  half  an  inch  thick  over  the 
most  prominent  portion  of  the  die.  As  in  making  dies,  time  is  saved  by 
arranging  on  the  molding  bench  as  many  dies  as  are  to  be  covered 
and  pouring  a  number  in  succession.  After  the  counter-die  has  set, 
the  die  and  counter-die  are  removed  from  the  sand,  the  casting-ring 
removed,  and  after  brushing  from  them  the  loose  sand,  if  needed  im- 
mediately, they  may  be  chilled  in  cold  water.  Before  separating  the 
die  from  the  counter-die,  if  two  have  been  made  from  the  same  model, 
one  set  should  be  marked  by  a  hammer  blow  on  the  edge  of  both  die 
and  counter-die  so  as  to  know  to  which  die  each  counter-die  belongs. 
The  die  and  counter-die  are  readily  separated  by  a  few  sharp  blows  on 
the  die  with  the  swaging  hammer  in  a  direction  to  drive  the  die  out  of 
the  counter-die.  In  most  cases  thty  fall  apart  readily;  in  some  cases, 
however,  where  there  are  undercuts,  they  must  be  cautiously  coaxed 
apart  by  light  blows  first  on  one  side  and  then  on  the  other,  otherwise 
the  die  may  be  broken  and  ruined. 

The  dies  should  now  receive  a  careful  inspection,  and  the  final  prepa- 
ration for  use.  Where  two  have  been  made  from  the  same  model, 
the  best  is  reserved  for  the  final  swaging.  If  not  previously  done,  the 
teeth  should  be  cut  from  the  first  die  used  for  partial  plates,  and  any 
carving  necessary  to  correct  inaccuracies  completed. 

LOW   FUSING  ALLOY    DIES   AND   COUNTER-DIES   FOR 
SPECIAL   USE. 

Now  and  again,  the  so-called  fusible  metals  can  be  advantageously 
used  for  making  dies  and  counter-dies.  Dies  for  small  plates  to  be 
made  of  thin,  soft,  high  carat  gold,  may  be  made  of  these  low  fusing 
alloys  cast  into  plaster  or  moldine  impressions  of  that  portion  of  the 
model  which  the  plate  is  to  cOver,  the  counter-die  being  also  made  of 
the  same  alloy,  saving  not  only  time,  but  the  expense  and  trouble  of 
melting  the  less  fusible  metals.  In  repair  work,  the  low  fusing  alloy 
may  be  cast  upon  a  gold,  silver,  or  vulcanite  plate  with  perfect  safety, 
when  a  die  is  needed  to  fit  a  re-enforcing  piece  to  an  irregular  surface. 
It  may,  in  some  cases,  be  cast  upon  a  plaster  model  direct,  thus  mak- 
ing the  counter-die  first,  the  die  being  made  by  using  it  as  an  impres- 
sion. Wliile  dies  and  counter-dies  of  low  fusible  alloys  are  not  hard 
enough  for  serious  work  in  swaging,  and  are  too  brittle  to  withstand  heavy 
hammer  blows,  they,  nevertheless,  serve  a  useful  purpose  in  forming 


334  DIES,    COUyTEIl-DIES  AND   MOLDING. 

soft  and  pliable  nu'tals.  Instead  of  usinji;  a  liammer,  the  swaging  may 
be  done  l)etween  the  jaws  of  the  bench  vise,  or  in  tlie  "shot-swage."  To 
get   the  best    results   with  low  fusing  allovs  thev  should  not  be  over- 

^^  Oil 

heated,  nor  yet  poured  when  quite  fluid.  Just  before  setting  they 
assume  a  plastic  condition,  and  then  make  a  harder  and  smoother 
die.  In  order  to  prevent  the  two  dies  from  uniting  when  both  are 
made  of  low  fusing  alloy,  the  first  cast  should  })e  (|uite  cold,  and  the 
alloy  used  in  making  the  second  casting  should  be  as  cool  as  it  can  be 
poured.  Painting  the  surface  with  whiting  is  helpful,  but  unnecessary, 
if  proper  care  is  observed. 


CHAPTER    X. 

SECURING   THE   VARIOUS   DATA   TO  BE   USED   IN   CONSTRUCTING 
ARTIFICIAL  DENTURES.     TAKING  THE  BITE.     ARTICULATORS. 

By  Charles  R.  Turner,  D.D.S.,  M.D. 

In  addition  to  the  plaster  casts  which  represent  the  jaws  of  the 
patient,  other  data  are,  of  course,  necessary  for  the  design  and  con- 
struction of  artificial  dentures.  These  casts  must  be  placed  and  main- 
tained in  the  same  relative  position  to  each  other  during  the  subsequent 
stages  of  arranging  the  artificial  teeth  in  occlusion  as  the  jaws  they 
represent  are  to  occupy  when  the  finished  dentures  ha\'e  been  inserted 
and  are  brought  into  occlusion.  We  have  seen  in  Chapter  1\.  that 
when  the  natural  teeth  are  in  the  mouth  the  so  called  "position  of 
occlusion"  is  fixed  by  a  certain  definite  fitting  together  of  the  occlusal 
surfaces  of  the  teeth.  When  the  natural  teeth  have  been  lost,  the 
position  of  occlusion  no  longer  exists,  and  it  is  necessary  to  determine 
for  the  mandible  by  considerations  presently  to  be  discussed  a  position 
in  relation  with  the  maxilla  which  will  answer  the  requirements  of  an 
occlusal  position  for  the  artificial  dentures.  The  operation  of  securing 
a  record  of  this  relationship  in  accordance  with  which  the  casts  may  be 
molmted  upon  an  articulator,  an  instrument  designed  to  maintain 
them  in  it,  is  commonly  called  "taking  the  bite." 

Besides  the  securing  of  a  record  of  this  relationship,  it  is  necessary  to 
obtain  also  an  estimate  of  the  fulness  which  the  artificial  dentures  must 
possess  to  restore  the  external  contour  of  the  lips  and  cheeks,  and  to 
record  both  the  location  of  the  median  line  of  the  mouth  and  the  amount 
of  the  dentures  which  will  be  displayed  during  the  ordinary  movements 
of  the  lips  in  laughter  and  speech. 

But  it  is  not  enough  that  the  artificial  teeth  shall  occlude  properly; 
they  must  also  be  arranged  to  be  capable  of  functionating  to  the  best 
advantage  during  the  various  mandibular  movements  in  which  the  food 
is  masticated.  This  necessitates  during  their  arrangement  the  use  of 
a  so-called  "anatomical  articulator,"  an  instrument  which  is  capable 
of  reproducing  the  movements  of  the  mandible  of  the  person  for  whom 
the  dentures  are  being  constructed.  The  instrument  must  be  adjusted 
so  that  its  joint  mechanism  reproduces  the  temporo-mandibular  joint 
of  the  case  in  hand,  and  hence  the  movements  of  the  mandible.  A 
record  of  the  path  of  the  mandibular  condyles  during  these  movements 
or  its  equivalent  is  therefore  necessary.  In  order  that  the  casts  may 
be  mounted  upon  such  an  articulator  in  the  same  relationship  to  its 
joint  mechanism  as  the  jaws  they  represent  bear  to  the  temporo- 
mandibular joint,  a  record  of  this  relationship  must  also  be  obtained. 

.335 


336  JJATA   TO  BE   USED  IN  CONSTRUCTING  DENTURES. 

As  a  matter  of  convenience,  it  is  usually  customary  at  this  time  to 
select  the  shade  of  artificial  teeth  suitable  for  the  patient  under  con- 
sideration in  accordance  with  principles  to  be  outlined  in  a  succeeding 
chapter. 

To  recapitulate,  the  data  which  are  to  be  obtained  are: 

1.  Relationship  of  the  jaws  in  the  position  of  occlusion. 

2.  Fulness  of  plates  necessary  to  restore  external  contours. 

3.  Median  line  of  mouth. 

4.  Amount  of  dentures  displayed  in  movements  of  lips.  (High  lip 
line.) 

5.  Relationship  of  the  jaws  to  the  temporo-mandibular  joint. 

6.  ^Movements  of  the  mandible. 

7.  Shade  of  artificial  teeth. 

These  are  usually  included  under  the  term  "taking  the  bite,"  which  by 
an  extension  of  its  old  meaning  has  now  come  to  commonly  cover  these 
several  operations.  It  originally  referred  to  the  first  of  these  pro- 
cedures, which,  as  first  in  point  of  time  and  probably  of  importance,  is 
now  to  be  discussed. 

SECURING  THE  RELATIONSHIP  OF  TI^E  JAWS  IN  THE  POSITION 
OF    OCCLUSION.     TAKING    THE    BITE. 

If  it  were  required  to  make  an  artificial  denture  for  an  edentulous 
case  immediately  after  the  teeth  were  lost,  and  if  it  were  possible  to 
obtain  a  record  of  what  the  occlusal  relationship  of  the  jaws  was  before 
the  loss  of  the  teeth,  this  would  of  course  serve  for  the  setting  up  of  the 
artificial  teeth,  and  the  dentures  would  then  establish  the  mandible  in 
a  correct  occlusal  position.  As  no  data  are  obtainable  which  will 
enable  the  dentist  to  tell  what  this  was,  and  as  the  changes  in  the  tissues 
following  the  loss  of  the  teeth  soon  alter  the  requirement  of  an  occlusal 
relationship  of  the  jaws  for  artificial  dentures,  an  occlusal  position  for 
the  mandible  must  be  determined  by  the  considerations  now  to  be 
discussed. 

^Vhen  the  teeth  have  been  lost,  the  position  of  the  mandible  is 
determined  by  the  balance  estabhshed  between  the  muscles  which 
actuate  it  within  the  restriction  offered  by  the  temporo-mandibular 
joint.  One  characteristic,  however,  of  the  occlusal  position  when  the 
natural  teeth  remain  is  that  the  condyles  occupy  the  most  distal  posi- 
tion in  the  glenoid  fossae  which  they  can  assume.  This  distal  position 
of  the  condyles  is  one  of  the  requirements  for  the  occlusal  position  of 
the  mandible  for  an  edentulous  case.  It  is  only  in  such  a  position 
that  the  muscles  can  be  free  from  strain  and  the  jaw  be  in  a  state  of 
equilibrium.  This  position  of  the  condyles  is  the  ultimate  one  reached 
by  them  from  the  various  movements  incident  to  mastication,  and  the 
artificial  teeth  must  be  arranged  so  that  w^hen  the  condyles  reach  this 
point  the  teeth  Avill  fit  together  in  proper  occlusal  relationship. 

With  the  condyles  of  the  edentulous  mandible  in  their  most  distal 
position  in  the  glenoid  fossae,  only  the  movement  of  its  anterior  end  as 
it  is  raised  or  lowered  bv  the  muscles  has  to  be  reckoned  with.     This 


BITE-PLA  TES.  337 

simply  means  that  It  has  to  be  estahhshed  a  certaui  (Hstance  from  the 
upper  jaw,  and  this  distance  is  determined  wholly  by  considerations 
relating  to  the  appearance  of  the  tissues  of  the  face.  This  latter  is  the 
only  available  guide  by  which  the  position  of  the  mandible  can  be 
fixed,  and  it  must  be  such  that  the  contours  and  proportions  of  the  face 
are  harmoniously  arranged.  Were  it  possible  to  keep  the  condyles  in 
the  back  part  of  their  fosste  at  all  times  during  the  determination  of  the 
position  of  its  anterior  end,  it  would  be  simple  enough  to  secure  a  satis- 
factory occlusal  position  for  the  mandible.  It  would  then  be  only 
necessary  to  hold  the  jaws  apart  the  amount  dictated  by  a  correct 
judgment  of  the  case  in  hand  when  the  occlusal  position  would  have 
been  found.  But  as  will  be  seen  later,  it  is  very  difficult  to  get  and  to 
keep  the  condyles  back  in  their  fossae  during  such  manipulations,  so  it 
is  necessary  to  solve  the  problem  by  a  different  method.  This  consists 
in  providing  a  means  of  maintaining  the  jaws  a  certain  distance  apart 
(already  ascertained  as  proper  for  the  case  in  hand)  and  then  to  induce 
the  condyles  to  slide  back  to  their  most  distal  position.  This  is  the 
rationale  of  all  proper  bite-taking  methods. 

In  securing  this  relation  it  is  necessary  to  make  use  of  plates  which  fit 
the  jaws,  and,  by  aftording  mutual  bearing  surfaces,  provide  a  means  of 
keeping  them  a  definite  distance  apart.  If  these  plates  are  fixed  to- 
gether while  the  jaws  are  in  the  occlusal  position,  they  thus  make  a  record 
of  it,  so  that  the  casts  may  be  mounted  in  the  articulator  in  accordance 
therewith.  They  serve  also  as  a  means  of  recording  the  other  data 
mentioned  above,  and  as  a  guide  in  mounting  the  teeth.  They  are  called 
"bite-plates." 

BITE-PLATES. 

By  reason  of  the  temporary  nature  of  its  service  it  is  desirable  that 
the  bite-plate  should  be  made  of  a  material  which  will  admit  of  being 
molded  into  requisite  form  over  the  cast  and  without  injury  to  it. 
Sufficient  rigidity  at  the  temperature  of  the  mouth  to  insure  the  firm 
retention  of  the  bite-plate,  and  sufficient  hardness  to  prevent  change 
in  its  shape  while  in  use,  are  qualities  which  it  must  possess.  Be- 
cause of  the  fact  that  its  original  form  is  wholly  tentative,  as  the  plate 
must  be  trimmed  or  enlarged  to  meet  indications  when  the  bite  is 
taken,  the  material  should  also  readily  allow  these  changes.  Wax  and 
its  various  combinations,  as  pink  paraffin  and  wax,  white  wax,  etc.,  are 
the  substances  in  most  common  use  for  this  purpose,  but  they  are  open 
to  the  objection  that  they  are  not  hard  enough,  nor  are  they  sufii- 
ciently  rigid  at  body  temperature  unless  used  in  such  amounts  as  to 
make  the  plates  unwieldly.  Gutta  percha  and  wax,i  ideal  base  plate,' 
and  other  materials  of  greater  stiffness  have  been  used.  Of  the  molded 
materials,  modelling  compound  seems  to  possess  the  largest  number  of 
qualities  to  recommend  it,  while  objections  to  it  may  be  overcome  by 
attention  to  the  details  of  its  use,  as  vdW  be  seen  later.  Because  of  their 
rigidity,  bite-plates  swaged  of  ^-acuum-chambe^  metal^  and  other  soft 

1  Evans.  2  Head. .  ^  Essig. 

22 


>38 


DATA    TO  BK    USED   L\   CONSTRUCTISG   DENTURES. 


metals  have  been  used,  the  occlusal  portion  of  the  plate  beinij  made  of 
one  of  the  heat-softened  materials.  The  amount  of  time  necessary  to 
execute  the  various  steps  in  the  making  of  swaged  bite-plates  for  den- 
tures to  be  made  of  one  of  the  molded  bases  is  so  serious  a  drawback  to 
the  method  that  in  most  instances  it  is  impracticable,  but  their  advan- 
tages should  not  be  forgotten  in  deaHng  with  difficult  cases. 

For  the  Upper  Jaw. — To  construct  a  bite-plate  of  modelling  com- 
pound for  the  upper  jaw,  the  cast  should  be  placed  upon  its  base  on 
the  work  bench  with  the  distal  portion  toward  the  operator.  (Fig. 
309.)  The  plate  outline  should  have  been  marked  upon  it,  but  the 
placing  of  the  vacuum-chamber  form,  and  any  alteration  of  the  face 
of  the  cast  by  additions  of  tin-foil  for  retention  purposes,  should  be 


Fig.  309 


Steps  in   t 


deferred  until  a  subsequent  time,  because  they  would  probably  be  dis- 
turbed in  the  forming  of  the  bite-plate.  The  method  of  making  the  })ite- 
plate  in  one  piece  proposed  by  Dr.  W.  W.  Evansi  is  to  be  recommended. 
Three-fourths  of  a  cake  of  modelling  compound  is  softened  in  warm 
water,  kneaded  in  the  hands  until  homogeneous,  anrl  rolled  into  an  ellip- 
soid about  two  inches  long.  One  side  of  this  should  be  thinned  out  by 
pressure  between  the  fingers,  and  the  mass  so  i)laced  upon  the  cast  that 
the  thinned  portion  ])rojects  slightly  beyond  the  posterior  margin  of  the 
plate  outline.  By  manipulation  with  the  thumbs  the  remainder  of  the 
compound  is  gradually  worked  forward  so  that  the  vault  of  the  cast  is 
covered  by  it  to  the  thickness  of  about  ^\  of  an  inch.  The  thickness 
of  this  maV  be  readily-  gauged,  for  the  cast  chills  the  material  as  it  come? 

•  International  Dental  Journal.,  vol.  xx.,  p.  221. 


BITE-PLATES.  339 

ill  contact  with  it,  thus  liardcMiini;-  it,  wliile  tlie  overlyiiis^  soft  portion 
may  he  pushed  forward.  When  the  top  of  the  alveohir  ridge  has 
been  reached,  the  compound  should  be  carried  over  it  and  sUghtly  be- 
yond the  jJate  outUne,  along  the  labial  and  buccal  surfaces,  the  most 
of  the  mass,  however,  remaining  upon  the  ridge  and  being  shaped  to 
represent  tlie  occlusal  portion  of  the  bite-plate.  The  pr()l)al)le  relation 
of  this  part  of  tlie  artificial  denture  to  the  alveolar  ridge  and  the  prob- 
able fulness  of  the  buccal  and  labial  portions  should  be  borne  in  mind 
and  the  compound  disposed  accordingly,  since  the  bite-plate  when 
completed  should  be  a  rough  model  for  the  denture  in  these  particulars. 
It  should  be  taken  from  the  cast,  chilled  in  cold  water,  and  trimmed 
around  its  periphery  to  the  plate  outline.  It  ought  then  to  be  replaced 
upon  the  cast  and  its  margin  brought  into  close  contact  therewith, 
around  the  plate  outline.  This  is  to  insure  firm  retention  of  the  plate 
in  the  mouth,  which  is  of  the  greatest  importance,  and  should  be  secured, 
even  if  it  be  necessary  to  make  at  this  time  the  changes  in  the  sur- 
face of  the  cast  which  provide  for  the  adhesion  of  the  future  denture. 
The  form  of  the  bite-plate  at  this  time  is  largely  tentative,  as  it  is  pur- 
posed to  complete  its  modelling  when  the  bite  is  taken,  in  accordance 
with  the  requirements  which  shall  then  be  indicated.  During  the 
process  of  forming  the  plate,  to  prevent  adhesion,  the  hands  should  be 
wet  and  the  compound  occasionally  taken  off  the  cast  to  break  up  its 
adhesion  while  it  is  soft,  and  then  replaced,  but  under  no  circum- 
stances must  the  cast  be  wet,  as  this  will  injure  it  for  subsequent  use. 
Rubbing  its  surface  with  soapstone  or  talcum  powder  will  effectually 
prevent  the  adhesion  of  the  compound. 

It  is  possible  to  construct  the  plate  in  two  portions,  that  in  contact 
\\\t\\  the  mucous  membrane  being  made  of  one  piece  of  modelling  com- 
pound rolled  into  a  thin  sheet  and  adapted  to  the  cast,  that  representing 
the  occlusal  portion  being  formed  of  a  roll  bent  to  the  shape  of  the  ah-eo- 
lar  ridge,  and  made  to  adhere  by  dry  heat.  The  occlusal  portion  is 
made  of  wax  by  some  practitioners  because  of  the  greater  ease  with 
which  it  may  be  carved,  but  its  softness  and  tendency  to  yield  under 
pressure  make  it  less  safe  than  modelling  compound  in  preserving  a 
fixed  distance  between  the  jaws. 

The  Lower  Bite-plate. — The  lower  bite-plate  is  more  easily  made 
than  the  upper.  With  the  cast  face  up  on  the  work-bench,  a  piece  of 
compound  equal  to  about  one-half  of  a  sheet  is  softened  and  worked 
into  a  long  uniform  r.oll,  bent  to  the  shape  of  the  alveolar  process,  and 
placed  upon  its  summit.  (Fig.  310.)  With  the  thumbs  and  fingers 
it  is  worked  down  the  lingual  and  labial  sides  to  a  point  slightly  be- 
yond the  plate  outline,  that  portion  over  the  ridge  being  shaped  to 
represent  this  part  of  the  future  lower  plate  and  made  to  correspond  in 
outline  to  the  arch  of  the  upper  bite-plate.  It  is  removed  and  trimmed 
to  the  plate  outline  like  the  upper,  its  occlusal  surface  being  left  rough. 
If  the  lower  plate  must  be  very  thin,  it  may  be  strengthened  by  im- 
bedding in  it  a  piece  of  iron  or  brass  wire  shaped  to  conform  to  the 
alveolar  outline. 


S-tO  DATA    TO  BE   USED  IN  CONSTRUCTING  DENTURES 

In  taking  the  bite  for  a  swaged  or  cast  metal  plate,  for  a  continuous- 
gum  denture,  or  for  a  vulcanite  plate  where  the  base-plate  has  been 
previously  vulcanized,  the  base-plate  itself  is  used  for  the  bite-plate 
with  an  addition  of  modelling  compound  ovev  the  alveolar  ridge  to  give 
it  an  occlusal  surface. 

Technique  of  the  Operation. — The  securing  of  the  relation  between 
the  jaws  may  be  divided  into  two  stages — the  fitting  and  shaping  of  the 


Steps  in  the  formation  of  a  bite-plate  for  a  full  lower  case 


bite-plates,  and  the  use  of  them  in  securing  the  relation  of  the  jaws  in 
the  position  of  occlusion. 

The  patient  should  be  seated  in  an  erect  position  in  the  dental  chair. 
(Figs.  311,  312.)  The  upper  bite-plate  is  first  tried  in  and  the  plate 
outline  followed  by  it  verified  or  corrected  if  necessary.  It  is  essential 
to  the  success  of  the  operation  that  the  bite-plate  should  remain  firmly 
in  position  and  it  should  be  trimmed  where  any  movable  tissues  tend  to 
displace  it.  Its  adhesion  may  be  improNed  by  scraping  from  the  centre 
of  the  palatal  side  to  relieve  pressure  at  this  point  and  by  accentuating 
the  contact  of  its  periphery  by  bending.  It  should  then  be  observed 
whether  the  buccal  and  labial  portions  of  the  plate  restore  the  contours 
of  the  lip  and  cheek  tissues  which  they  support,  in  accordance  mth  prin- 


TECHNIQUE  OF  THE  OPERATION. 


341 


ciples  contained  in  Chapter  XII.,  and  the  plate  added  to  or  trimmed  as 
may  be  indicated.  ^Yhile  the  modellinf>'  in  these  regions  cannot  be 
completed  at  this  stage,  it  is  advisable  to  have  the  form  answer  the  re- 
quirements of  contour  as  fully  as  may  be  possible.  The  inclination  of 
the  occlusal  portion  of  the  plate  to  the  ridge  may  be  changed  by  reheat- 
ing in  water  and  bending  after  replacing  it  upon  the  cast,  but  additions 
of  compound  to  the  plate  should  be  made  to  adhere  by  means  of  dry 
heat  applied  to  the  two  surfaces,  by  which  means  its  adhesive  property 
is  best  developed.  Any  trimming  may  be  easily  done  while  the  mate- 
rial is  slightly  warm,  as  it  may  be  cut  with  a  knife  without  dragging 
at  this  stage,  and  as  it  becomes  brittle  and  hard  when  cold. 

A  most  important  point  of  reference  which  will  be  utilized  in  the  con- 
struction of  the  denture  and  which  determines  the  length  of  the  occlusal 


Fig.  311 

K 

1^^^. 

1^1 

^ 

M 

*. 

^^^1hi^^» 

p^.,.^^ 

Fig.  312 


Patient    with   edentulous   jaws.     Front    view. 
Preparatory  to  taking  the  bite. 


Patient   with   edentulous   jaws.     Profile   view. 
Preparatory  to  taking  the  bite. 


portion  of  the  bite-plate  is  now  noted.  This  is  the  lower  margin  of  the 
upper  lip  when  in  repose.  This  should  be  marked  upon  the  labial 
surface,  and  the  occlusal  portion  of  the  plate  trimmed  to  wdthin  one-six- 
teenth of  an  inch  of  this,  so  that  the  plate  will  project  that  amount 
below  the  lip.^  (Fig.  313.)  The  anterior  portion  of  the  bite-plate 
should  not  be  trimmed  or  added  to  in  subsequent  fitting  together  of  the 
two  plates,  as  the  lower  margin  of  this  surface  is  to  indicate  the  position 
of  the  incisive  edges  of  the  anterior  teeth  of  the  artificial  denture. 
The  distal  portions  of  the  occlusal  surface  should  be  trimmed  to  curve 
upward  in  accordance  with  the  probable  plane  of  occlusion  of  the  future 
denture. 

The  lower  bite-plate  is  now-  tried  separately  in  the  mouth,  the  plate 
outline  verified,  and  then  the  two  are  put  in  together.     The  length  of 

1  Dr.  A.  D.  Gritman. 


342 


DATA    TO  BE   USED  IX  CONSTRUCTING   DENTURES. 


the  iii)por  l)ite-j)late  haAin^;  been  (Infinitely  fixed,  it  is  i)ur[)()se(l  to  trim 
the  lower  one  so  that  when  in  oeclnsion  with  the  ui)per,  when  the 
condyles  are  in  the  most  distal  part  of  the  glenoid  fossae,  the  jaws 
will  be  held  apart  the  distance  it  has  been  decided  is  proi)er  for  them. 

If  it  were  possible  to  ascertain  what  the  occlnsal  position  of  the  man- 
dible was  when  the  natural  teeth  were  in  ])lace,  it  is  probable  tiiat  this 
would  fulfil  the  requirements  of  occlusion  for  the  artificial  dentures 
in  a  majority  of  cases,  although  when  the  teeth  have  been  out  some 
time  the  tissues  of  the  lips  and  cheeks  ha\e  contracted  and  accom- 
modated themselves  to  a  lessened  distance  between  the  jaws.  It  will 
be  necessary  to  determine  this  distance  by  a  judgment  based  upon 
the  external  appearance  of  the  face  and  particularly  that  of  the  mouth, 
and  as  this  is  affected  by  the  fulness  of  the  bite-plates  as  well  as  by 
their  length,  these  two  dimensions  should   l)e  considered   conjointly. 


Patient  with  full  upper  bite-plate  trimmed  to  one-sixteenth  inch  below  the  upper  lip. 

The  tentative  form  of  the  upper  bite-plate  is  sufficient  guide  in  the 
matter  of  contour  to  begin  with,  so  the  lower  plate  is  trimmed  to  what 
is  judged  to  be  its  proper  length,  and  the  contours  readjusted  subse- 
quently if  necessary,  or  if  later  alteration  of  the  buccal  or  labial  surfaces 
should  show  that  the  bite-plates  are  too  short,  they  must  receive  addi- 
tions to  meet  the  indications.  In  judging  of  the  final  contours,  three 
places  require  especial  attention.  (1)  The  lips  need  to  be  supported 
at  their  point  of  contact,  as  the  margins  fall  in  when  the  teeth  have  been 
lost.  This  is  provided  for  by  the  amount  of  projection  of  the  bite- 
plate  at  the  point  corresponding  to  the  edges  of  the  upper  incisors,  and 
by  the  inclination  of  its  labial  surface.  (2)  As  a  great  deal  of  resorption 
has  taken  place  at  the  site  of  the  canine  tooth,  this  area  should  be  held 
out  by  the  bite-plate,  and  the  corner  of  the  mouth  given  proper  fulness. 
The  upper  bite-plate  must  be  fuller  and  higher  here  than  anywhere  else. 


TECHNIQUE  OF  THE  OPERATION. 


343 


(3)  The  other  place  at  which  fuhiess  is  often  required  is  at  the  site  of  the 
bicuspids  and  first  mohirs,  where  the  cheek  may  be  sunken  in. 

When  the  labial  surfaces  of  the  bite-plates  have  been  built  out  to 
proper  ])r()porti()ns,  the  distance  between  the  nose  and  chin  siiould  be 
such  that  the  lips  just  come  in  contact.  (Fig.  '314.)  When  the  proper 
position  has  been  obtained  an  equal  amount  of  the  mucous  surface  of 
both  lips  is  displayed,  the  upper  lip  is  inclined  outward  slightly  from  its 
base,  and  the  lower  lip  is  sufficiently  everted  to  bring  out  the  graceful 
curve  between  it  and  the  chin.  (Fig.  315.)  If  the  bite  is  too  long  the 
lips  will  be  strained  in  trying  to  cover  the  plates,  or  if  too  short,  they 
will  appear  compressed  or  curled  upon  themselves.  Where  the  teeth  have 
been  out  a  long  time  and  wdiere  the  tissues  have  wrinkled  in  consequence, 
it  is  impossible  to  take  out  all  the  wrinkles  or  to  establish  the  ideal  con- 
tour and  proportions  above  suggested;  and  this  is  also  true,  of  course, 


Fig.  314 


Patient    with    full    upper    and    lower   bite-plates 
in  place.     Front  view. 


Patient    with   full    upper    and    lower   bite-plates 
in  place.     Profile  view. 


where  they  were  not  originally  possessed.  It  should  be  remembered  that 
during  the  fitting  and  trimming  of  the  plates  the  condyles  of  the  lower 
jaw  must  be  kept  in  their  most  distal  position.  When  they  have  once 
been  secured  in  this  position,  the  lower  bite-plate  should  have  its  labial 
surface  marked  and  trimmed  or  built  out  until  it  is  flush  with  that  of  the 
upper  bite-plate.  During  subsequent  manipulations  the  relationship  of 
these  labial  surfaces  is  a  guide  as  to  whether  or  not  the  condyles  are  in 
their  correct  distal  position.  In  some  cases  patients  have  contracted  the 
habit  of  protruding  one  condyle,  thus  throwing  the  lower  bite-plate  to 
one  side.  In  such  instances  it  will  be  found  advantageous  to  mark  the 
median  line  of  the  face  upon  upper  and  low'er  bite-plates  at  this  junc- 
ture, being  certain  that  both  condyles  are  retruded  at  the  time.  Dur- 
ing subsequent  procedures  lack  of  correspondence  in  these  two  lines 
will  at  once  indicate  a  protrusion  of  one  condyle. 


344 


DATA    TO  BE   USED  IN  CONSTRUCTING  DENTURES. 


The  lower  bite-plate  must  be  trimmed  to  occlude  e\enly  with  the 
upper  throughout  its  whole  extent,  and  when  the  mouth  is  closed  the 
contact  between  the  two  should  be  equal  at  all  points.  It  is  important 
that  the  bite-plates  should  be  evenly  trimmed ,  since  there  is  danger 
that  they  may  be  in  contact  anteriorly  and  aj)pcar  to  be  i:)()steriorly, 
when  they  are  really  too  short,  and  have  been  forced  oft'  the  ridge  by 
leverage  on  their  anterior  portions,  and  it  is  wise  to  leave  the  lower 
bite-plate  longer  behind  than  in  front  and  trim  it  to  accord  therewith. 
\Vhen  the  plates  have  been  fitted  by  trimming  as  closely  as  possible,  an 
absolute  fit  may  be  obtained  by  removing  the  lower  bite-plate  and 
very  slightly  softening  its  occlusal  surface  over  an  open  flame,  quickly 
returning  it  to  the  mouth,  and  having  the  patient  close  in  the  occlusal 
position,  gently  pressing  the  plates  together.     It  is  important  tliat  in 


Fig.  31G 


Fig.  317 


Patient    with   bite-plates   of  correct    fulnes.s,  but 
too  .short. 


Patient    with   bite-plates  of   correct    length   not 
full  enough. 


this  procedure  the  uj^per  bite-plate  be  kept  cool  enough  not  to  ha\e  its 
form  altered  at  all.  The  final  fitting  may  be  conveniently  judged  by 
placing  the  index-finger  of  each  hand  in  the  mouth  in  contact  with  the 
buccal  surfaces  of  the  two  plates,  which  serves  to  hold  them  on  the  al- 
veolar ridges,  and  by  pressing  the  ball  of  the  finger  slightly  l)etween  the 
occlusal  surfaces  of  the  plates  as  the  patient  is  directed  to  close  the 
mouth  slowly,  they  are  held  apart  at  places  where  they  do  not  fit  prop- 
erly. These  occlusal  portions  afford  rigid  and  unyielding  surfaces  that 
maintain  the  jaws  apart  the  distance  which  has  been  decided  upon. 
The  bite-plates  so  fitted  should  now  be  removed  from  the  mouth. 
Their  occlusal  portions  should  be  trimmed  down  from  the  inside  until 
they  are  not  more  than  three-eighths  of  an  inch  wide.  This  is  to 
give  room  to  the  tongue  and  to  make  them  as  comfortal)le  as  possible 
for  the  patient.     It  may  be  stated  that  the  more  nearly  they  approx- 


TECHNIQUE  OF  THE  OPERATION.  345 

imate  the  future  denture  in  form  and  size,  the  greater  will  be  the  hke- 
lihood  of  accuracy  in  taking  the  bite.  They  should  have  grooves  cut 
upon  their  occlusal  surfaces,  as  illustrated  in  Figs.  31S  and  .319,  trans- 
verse ones  at  the  site  of  the  first  molar  and  first  bicuspid  teeth,  and  a 
longitudinal  one  between.  The  grooves  receive  the  wax  to  be  used 
later  in  fixing  the  plates  together. 

Having  thus  determined  by  means  of  the  rigid  occluding  surfaces 
of  the  bite-])lates  what  the  distance  between  the  jaws  shall  be,  the 
second  stage  consists  in  securing  the  mandible  in  such  position  that 
the  plates  are  in  contact  and  the  condyles  are  back  in  the  glenoid 
fossae,  and  the  position  of  occlusion  is  obtained.  If  the  bite-plates 
are  then  fixed  together  and  taken  from  the  mouth,  the  casts  may  be 
placed  in  position  in  them  and  mounted  upon  the  articulator.     The 

Fig.  318  Fig.  319 


Full  upper  bite-plate,  with  yellow  wax  on  occlusal       Full    lower   bite-plate,    showing   grooves   cut   on 
surface.  occlusal  surface. 

difficulty  which  presents  itself  in  this  procedure  is  in  getting  the  con- 
dyles back  in  the  fosste. 

When  the  natural  teeth  are  in  the  mouth  consciousness  of  the  occlusal 
relation  is  derived  from  sensations  transmitted  through  the  teeth,  which 
are  sensitive  tactile  organs  and  give  instant  knowledge  of  the  position 
of  the  mandible  w^henever  they  are  in  contact.  Absence  of  muscular 
strain  and  absence  of  a  strained  feeling  at  the  joint  also  contribute  to  a 
knowledge  of  this  occlusal  relation,  but  the  muscular  apparatus  itself 
does  not  possess  a  sufficiently  accurate  muscle  sense  to  convey  this  in- 
formation. If  the  mandible  is  not  forM^ard  of  the  incisive  relation  the 
inclined  planes  of  the  cusps  of  the  teeth  form  guides,  which  serve  to 
insure  its  return  to  the  occlusal  position  when  the  elevators  are  con- 
tracted. At  the  posterior  end  of  the  mandible  the  fossae  present  in- 
clined surfaces  which  serve  as  guides  to  the  condyles  in  their  return  to 
the  distal  position  occupied  by  them  during  occlusion.  With  the 
teeth  missing  we  have  only  the  temporo-mandibular  joints  as  guides 
in  directing  the  mandible  back  to  the  occlusal  position.  A  further 
consideration  of  this  joint  will  serve  to  give  a  clearer  understanding  of 
the  problem  under  discussion. 

The  temporo-mandibular  articulation  is  a  condyl-arthrodial  joint. 
Into  the  glenoid  fossa,  which  at  its  posterior  extremity  presents  a 


346  DATA    TO  BE   USED  IN  COySTRUCTINO   DENTURES. 

marked  concavity,  fits  the  condyle  of  the  lower  jaw,  with  the  interarticu- 
lar  fibro-cartilaije  interposed  between  them.  The  condyle  is  attached 
to  the  rim  of  the  fossa  1)\'  means  of  the  capsular  liuament,  to  tlie  centre 
of  which  latter  the  cartilage  is  attached.  The  li,i;ament  thus  hinds  the 
condyle  in  its  fossa  and  imposes  certain  limitations  upon  its  movement. 
The  anterior  portion  of  the  fossa  presents  a  flat  articular  surface  over 
which  the  condyle  and  cartilaii;e  ma\'  glide  in  the  various  movements 
of  the  maiKhhle.  During  the  protrusive  mo\enients  of  the  jaw  this 
arrangement  permits  the  condyle  to  slide  forward  upon  the  floor  of  the 
glenoid  fossa,  in  which  movement  it  is  accompanied  by  the  cartilage. 
At  any  time  during  this  forward  movement  the  mandible  may  rotate 
about  a  horizontal  axis,  passing  through  the  condyles  as  they  rest  on  the 
cartilages,  and  a  combination  of  these  two  movements  frecjuently  takes 
place.  These  movements  may  be  bilaterally  symmetrical  or  there  may 
be  movements  of  one  condyle  forward  and  inward,  the  other  remaining 
in  the  distal  part  of  the  fossa.  When  the  mandible  is  depressed  the 
condyles  also  slide  forward  in  the  glenoid  fossa.  This  is  due  to  several 
anatomical  peculiarities  of  the  joint  as  well  as  to  the  fact  that  external 
pterygoid  muscles  pull  forward  both  the  condyles  and  cartilages. 
The  external  and  internal  lateral  ligaments  are  attached  to  the  neck 
of  the  condyles  and  extend  so  far  forward  in  their  attachment  to  the  rim 
of  the  fossae  that  they  serve  as  falcrums  to  force  the  condyle  forward 
during  the  depression  of  the  mandible. 

In  returning  to  the  position  of  occlusion  from  any  of  these  excursions 
it  is  by  retraction  and  elevation  or  some  combination  of  these  movements 
according  to  the  position  from  which  the  return  is  made.  Normally 
this  is  accomplished  by  the  contraction  of  the  massetcr,  temporal,  and 
internal  pterygoid  muscles,  sometimes  in  combination  with  the  muscles 
attached  to  the  anterior  end  of  the  mandible.  By  the  contraction  of 
the  elevators  the  main  l)()dy  of  the  jaw  is  drawn  upward  and  backward 
when  the  condyles  slide  up  the  inclines  of  the  glenoid  fossae  into  their 
most  distal  parts.  The  lower  fibres  of  the  temporal  muscle,  the  inner 
lEibres  of  the  internal  pterygoid,  and  the  posterior  fibres  of  the  masseter 
muscles  serve  to  draw  the  jaw  back,  opposing  the  action  of  the  external 
pterygoid,  though  not  directly  in  line  with  it.  F'or  complete  retraction 
to  occur  there  must  be  total  relaxation  of  the  external  pterygoid,  as 
these  muscles  have  the  power  of  fixing  the  contlyles  at  any  point  in  their 
return  path.  If  the  condyles  are  thus  fixed  at  any  point  before  their 
most  distal  position  is  reached,  the  elevation  of  the  mandible  may  con- 
tinue by  rotation  about  this  now  fixed  axis.  When  the  anterior  end 
of  the  mandible  is  completely  elevated  it  will  then  be  forward  of  the 
occlusal  relation,  when,  if  the  natural  teeth  are  present,  their  contact 
serves  to  give  information  of  the  fact.  But  with  the  edentulous  patient 
this  source  of  knowledge  is  removed,  and  he  is  iniable  to  assist  in  the 
operation  of  securing  the  proper  occlusal  relationship.  Even  though 
there  is  a  complete  understanding  on  the  part  of  the  patient  as  to  what 
is  required,  he  no  longer  possesses  the  means  of  judging  if  this  is  ob- 


TECHNIQUE   OF   THE   OPERATION.  347 

tained,  and  his  efforts  are  not  only  not  hel[)fnl,  but  often  greatly  hinder 
the  work  of  the  dentist. 

After  the  loss  of  the  teeth  changes  in  the  joint  incident  to  this  con- 
dition freciuently  further  complicate  the  problem  at  hand.  The  elevator 
group  of  muscles,  being  no  longer  accommodated  to  a  fixed  position  of 
the  mandible,  usually  shorten,  as  do  the  other  tissues  extending  between 
the  jaws.  The  ligaments  of  the  joints  become  stretched  and  the 
articulation  becomes  loose  and  wandering.  The  anterior  portion  of  the 
glenoid  fossa  becomes  absorbed,  resulting  in  a  flattening  of  its  floor,  all 
of  which  factors  tend  to  make  the  protrusive  movements  easy  and  those 
of  retraction  uncertain.  The  longer  the  teeth  have  been  absent,  the 
greater  will  be  the  tendency  toward  protrusive  movements.  Lack  of 
precision  in  the  movement  of  the  jaw  will  also  frequently  be  increased 
by  the  various  manipulations  incident  to  fitting  the  bite-plates. 

It  becomes  very  difficult,  therefore,  to  secure  the  jaw  in  its  distal 
position.  In  this  operation  eflforts  are  directed  to  compel  the  patient 
to  close  the  mouth  and  bring  the  bite-plates  together,  and  to  have  the 
jaw  slide  back  to  its  proper  position.  Measures  which  are  utilized  to 
fix  the  plates  together  at  the  same  time  that  the  mouth  is  closed  are 
open  to  the  criticism  that  they  serve  to  increase  the  protrusive  tendency 
if  much  force  has  to  be  exerted  in  bringing  the  jaws  together,  and  great 
care  must  be  taken  to  avoid  this  error.  It  may  be  stated  as  a  truism 
that  the  smaller  the  amount  of  force  necessary  to  close  the  jaws,  the  less 
likelihood  will  there  be  of  protrusion.  Goslee^  has  called  attention  to  the 
tendency  to  a  continuation  of  the  incising  relation  which  may  be  caused 
by  having  too  much  wax  upon  the  anterior  part  of  the  plates.  This 
offers  the  same  sort  of  resistance  to  the  closure  of  the  jaw  as  is  met  with 
in  incising  food,  and  the  muscular  movements  which  are  useful  in  inci- 
sion are  reflexly  provoked  thereby.  Instructing  the  patient  "  to  bite" 
usually  conveys  the  idea  "to  incise,"  that  being  the  common  meaning 
of  the  word,  and  the  movements  of  that  operation  are  suggested.  It 
is  safest  to  use  the  term  "close  the  mouth"  in  giving  directions  during 
the  procedure,  as  that  more  nearly  than  any  other  suggests  the  desired 
movement. 

The  operator  must  be  able  to  tell  when  the  jaw-  is  in  its  posterior 
position,  in  which  he  may  be  assisted  by-.palpation  of  the  external  end  of 
the  condyle,  and  by  inspection  of  the  surface  of  the  skin  during  its 
motions,  and  by  resorting  to  the  measures  which  induce  its  backward 
movement.  While  it  is  there,  the  bite-plates  must  be  marked  and  so 
trimmed  that  their  anterior  surfaces  are  flush,  to  serve  during  sub- 
sequent procedures  as  an  indication  as  to  whether  the  jaw  is  protruded. 
The  median  line  may  also  to  advantage  be  marked  upon  both  plates  so 
that  a  protrusion  of  one  condyle  would  be  noted.  The  plates  should 
fit  firmly,  be  comfortable  and  stable  in  position,  and  the  patient  should  be 
engaged  in  conversation,  and,  if  possible,  made  to  forget  the  operation. 
Then  they  should  be  taken  out,  wiped  dry  with  a  napkin,  and  replaced. 

1  Transactions  Odontological  Society  of  Great  Britain,  1900,  p.  167. 

2  Taking  the  Bite.     The  Dental  Review,  vol.  xvii.,  p.  509. 


348  DATA   TO  BE   USED  IN  CONSTRUCTING  DENTURES. 

and  a  small  (|uaiitity  of  very  soft  yellow  wax  placed  over  the  grooves 
on  each  side  of  the  upper  plate.  The  patient  is  then  directed  toswallow, 
and,  as  the  lower  jaw  has  to  be  fixed  for  this  operation  to  give  a  base 
from  which  the  elevators  of  the  larynx  may  work,  the  condyles  are 
usually  forced  back  in  the  fossae.  By  this  means  the  patient  is  en- 
gaged in  the  performance  of  an  act  which  is  naturally  done  when  the 
condyles  are  back  in  their  fossne  and  the  tendency  to  protrusion  is 
thereby  considerably  reduced.  It  must  be  observed  that  the  bite-plates 
have  been  brought  into  the  proper  relation,  and  also  it  must  })e 
assured  that  they  are  in  position  on  the  ridges.  It  may  occasionally 
be  necessary  to  hold  them  in  position,  especially  in  the  case  of  a  lower 
jaw  in  which  there  has  been  much  absorption. 

If  the  head  is  thrown  backward  the  tissues  of  the  front  of  the  neck 
attached  to  the  lower  jaw,  particularly  the  platysma  myoides,  are  put 
on  the  stretch,  the  tendency  being  also  to  carry  the  jaw  backward.  In- 
structing the  patient  during  closure  of  the  mouth  to  touch  the  palatal 
vault  with  the  tip  of  the  tongue  as  far  posteriorly  as  possible  also,  has 
the  advantage  of  tending  to  keep  the  jaw  far  back.  Asking  the  patient 
to  bite  the  back  teeth  together  may  assist  in  securing  this  position,  be- 
cause of  the  fact  that  in  the  natural  denture  this  is  not  possible  when  the 
jaw  is  protruded.  Efforts  to  hold  the  jaw  back  })y  clasping  the  fingers 
behind  the  ligamentum  nuchae  and  pressing  with  the  thumbs  on  the 
chin,  or  pushing  it  back  forcibly  by  pressure  on  the  chin  during  the 
closing,  have  been  recommended  and  in  some  cases  they  may  be  suc- 
Pj^  32Q  cessful,  but  frequently  they  are  so  resisted  by 

the  patient  as  not  to  be  effective. 

Dr.  Molyneaux,  in  cases  of  extreme  diffi- 
culty, recommends  the  use  of  Garretson's  de- 
vice as  follows: 

"A  little  apparatus,  which  was  invented  by 
Dr.  Garretson,  of  Iowa,  has  been  satisfactorily 
emploved  in  several  cases,  and  is  illustrated  in 
Fig.  320. 

"It  consists  of  two  steel  strips  about  6  inches 
long,  at  one  end  of  which  are  projections  to 
enter  the  external  ear,  and  a  leather  strap  pass- 

Garretson's  device  for  keep-       iug  OVCr    tllC    OCciput    which    prCVCUtS    the    Caf 

ing  the  condyles  in  the  distal     pjeces  from  slipping  dowu.     At  the  Other  ends 

part  of  the  fossae  in  taking  the  oi  i  ••  i.  i,  i-i  i 

bite.  of  the  metal  strips  is  a  chin  plate  wliicli  works 

on  a  ratchet,  and  which  may  be  moved  for- 
ward or  backward  as  the  case  requires.  After  placing  the  ear  pieces 
in  position  and  tightening  the  straps,  the  chin  jilate  is  to  be  moved  up 
firmly  against  the  chin.  The  patient  should  now  open  and  close  the 
mouth  repeatedly,  and  as  the  lower  jaw  is  drawn  backward  the  chin 
plate  is  moved  upward  until  it  is  certain  that  the  condyles  are  at  rest 
in  the  glenoid  fossae.  In  this  position  the  patient  can  open  and  close 
the  mouth  comfortably,  but  any  attempt  at  protrusion  will  meet  with 
resistance  by  the  ear-lugs. 

"The  base  plates  are  then  adjusted  and  the  bite  is  taken  as  usual." 


THE  HIGH  LIP  LINE^  349 

The  wax  iutorposod  between  the  two  phites  should  be  small  in 
amount  and  cjuite  soft.  It  serves  two  purposes — to  unite  the  bite-plates 
in  the  position  of  occlusion  and  to  compensate  for  any  failure  of  their 
occlusal  surfaces  to  be  in  uniform  contact.  It  is  difficult  in  trimming  an 
unyielding  substance  like  modelling  compound  to  get  two  surfaces  to 
fit  absolutely  accurately,  although,  of  course,  this  should  be  attempted. 
The  wax  at  properly  distributed  points  offers  enough  resistance  to  hold 
the  plates  in  contact  with  the  membrane,  but  not  enough  to  interfere 
with  the  accuracy  of  closure.  Care  should  be  taken  to  see  that  the 
labial  surfaces  of  the  plates  are  flush,  since  by  this  means  it  may  be 
seen  that  the  jaw  is  in  its  most  distal  position.  The  bite  plates  may 
be  fixed  by  fusing  their  edges  together  with  a  hot  spatula,  or  by  the 
use  of  staples  of  wire  inserted  on  each  side  to  bind  them  together,  or 
in  very  difficult  cases  in  which  it  is  desired  to  interpose  no  resistance  to 
the  contact  of  the  bite-plates,  thin  plaster  of  Paris  may  be  used  for  the 
purpose  as  has  been  recommended  by  Ottolengui.^ 

The  High  Lip  Line. — In  the  usual  movements  of  the  lips  in  speaking 
the  teeth  are  more  or  less. exposed  to  view,  and  even  greater  display al  of 
the  denture  is  made  in  laughing  and  smiling.  The  relation  between  the 
lips  and  the  teeth  in  laughing  and  smiling  has  much  to  do  with  the 
beauty  of  these  acts.  It  is  usual,  therefore,  to  take  into  account  the 
amount  of  this  exposure  in  the  construction  of  artificial  dentures,  and 
the  highest  point  to  which  the  patient  can  elevate  the  upper  lip  should 
be  indicated  by  a  line  drawn  upon  the  upper  bite-plate  at  the  lower 
margin  of  the  upper  lip.  This  lip  is  more  mobile  than  the  lower, 
because  a  larger  number  of  muscles  move  it,  and  more  of  tlie  upper 
teeth  are  displayed  in  smiling  and  laughing.  In  separating  the  jaws 
the  lower  teeth  are  depressed  below  the  margin  of  the  lower  lip,  and 
it  is  usual  to  disregard  this  record  on  the  lower  bite-plate  for  the  addi- 
tional reason  that  the  upper  having  been  determined,  the  proportions 
of  the  lower  are  more  or  less  harmonious  therewith.  It  may,  however, 
be  marked  upon  the  lower  bite-plate  and  is  then  "the  low  lip  line." 

The  Median  Line  of  the  Mouth. — This  should  always  be  recorded,  for 
in  a  normal  natural  denture  the  line  between  the  central  incisors  prac- 
tically coincides  with  the  median  line  of  the  mouth.  The  median  line 
of  the  mouth  is  more  or  less  difficult  to  determine  for  lack  of  an  accu- 
rate guide  in  judging  it.  The  frsenum  of  the  upper  lip  is  usually  in  the 
median  line,  but  it  is  by  no  means  a  safe  landmark,  for  in  a  good  number 
of  cases  it  is  a  little  to  one  side  or  the  other.  The  median  line  of  the 
cast  and  the  little  tip  on  the  front  of  an  edentulous  upper  cast,  repre- 
senting the  incisive  pad  of  the  rugse,  are  also  unreliable ;  because  the  cast 
is  frequently  unsymmetrical  from  the  fact  that  the  teeth  on  one  side 
may  have  been  lost  earlier  and  the  resorption  taken  place  to  a  greater 
extent  than  on  the  other  side.  The  median  line  of  the  mouth  must, 
therefore,  be  secured  by  data  obtained  from  the  face.  The  tip  of  the 
nose  is  so  frequently  out  of  the  median  line  that  it  should  not  be  used. 
The  philtrum,  when  not  obliterated,  is  a  safe  point  of  reference.     The 

1  The  Dental  Cosmos,  vol.  xliv.,  p.  446. 


350  DATA    TO  BE   USED  IN  CONSTRUCTING  DENTURES 

base  of  the  septum  of  the  nose  and  the  median  Hne  of  the  chin  may  also 
be  used.  The  mouth  itseU'  is  sometimes  from  hal)it  or  otherwise  one 
sided,  and  then  the  Hne  fixed  upon  as  the  niechan  hne  should  occupy  a 
position  between  the  median  line  of  the  mouth  and  that  of  the  face. 
After  it  has  been  determined  upon,  it  should  be  marked  upon  both 
bite-plates  perpendicular  to  their  line  of  division  while  they  are  still 

Pig.  321  Fig.  322 


L'pper    and    lower  bite-plates   fixed  together  Bite-plate  for  full   upper  denture  in  case  in 

with  wax  and  showing  high  lip  line  and  median       which    the    lower    natural    teeth    remain.     Ca,st 
line  of  the  mouth.  set    in    bite-plate    preparatory    to    mounting    in 

articulator. 

in  the  mouth.     Fig.  321  shows  the  bite-plates  removed  from  the  mouth 
and  exhibits  the  median  and  high  lip  lines. 


BITES  FOR  FULL  UPPER  OR  LOWER  PLATES. 

The  bite  for  a  full  upper  plate  where  the  lower  natural  teeth 
remain  in  whole  or  in  great  part,  involves  the  construction  of  a  bite- 
plate  in  accordance  with  principles  already  outlined.  It  should  be 
tried  in  the  mouth,  trimmed  tentatively  for  contour  and  length  to  the 
lower  margin  of  the  upper  lip,  and  the  patient  requested  to  close  the 
lower  teeth  upon  it.  Special  care  should  be  taken  to  see  that  the  lower 
teeth  strike  evenly  upon  its  occlusal  surface,  and,  when  the  jaws  are* 
closed  in  the  position  of  occlusion,  the  lips  and  cheeks  should  be  lifted 
so  that  it  may  be  seen  whether  this  is  the  case,  and  an  excavator  should 
be  used  to  try  to  pry  the  jaws  apart  at  each  tooth  to  prove  the  contact. 
The  external  contour  and  distance  between  the  jaws  should  be  estab- 
lished in  accordance  with  the  principles  which  underly  their  determin- 
ation in  full  upper  and  lower  ca.ses.  After  the  plate  has  been  satisfac- 
torily shaped  to  fulfil  these  requirements,  it  is  removed  from  the  mouth, 
wiped  dry  with  a  napkin,  and  the  occlusal  surface  covered  with  a  thin 
layer  of  very  soft  yellow  wax,  which  should  be  made  to  adhere  closely, 
and  only  thick  enough  to  receive  indentations  of  the  occlusal  surfaces 
of  the  lower  teeth.  It  is  replaced  and  the  mouth  closed  as  in  the  pre- 
viously described  bite-taking  operations.      The  patient  should  bite 


BITES  FOR  FULL    UPPER   OR  LOWER  PLATES.  351 

into  the  wax  until  the  cusps  of  the  teeth  touch  the  bite-plate,  which 
insures  that  the  distance  between  the  jaws  is  the  same  as  was  deter- 
mined by  the  bite-plate.  It  is  important  that  only  a  small  amount  of 
wax  be  used  because  of  the  increased  tendency  to  protrusion  caused  by 
too  great  a  cjuantity.  The  bite-plate  may  be  marked  with  a  line  to 
note  the  position  between  the  lower  central  incisors  to  assist  in  bring- 
ing the  lower  jaw  to  a  correct  position,  and  the  relation  of  the  incisors 
to  the  edge  of  the  bite-plate  will  also  assist  in  this  purpose. 

The  high  lij)  line  and  median  line  of  the  mouth  should  be  marked 
upon  the  bite-plate,  since  the  line  between  the  lower  central  incisors  is 
too  frequently  out  of  centre  to  be  depended  upon  for  setting  up  the 
teeth,  and  the  median  line  of  the  mouth  is  a  safer  guide.  The  bite- 
plate  should  be  removed  from  the  mouth,  the  wax  chilled  in  water 
and  laid  aside,  and  an  impression  taken  of  the  lower  jaw,  a  cast  made 
and  fitted  into  the  depressions  in  the  wax  of  the  bite-plate.  (Fig.  322.) 
Bites  for  Full  Lower  Plates. — In  taking  the  bite  for  a  full  lower  den- 
ture, a  bite-plate  must  be  made  for  the  lower  jaw  as  described  earlier  in 
this  chapter.  It  rarely  occurs  that  the  upper  natural  teeth  remain 
in  a  mouth  in  which  all  the  lower  have  been  lost,  and  the  common 
case  requiring  a  full  lower  denture  is  that  in  which  there  is  already  a  satis- 
factory upper.  The  general  procedure  is  the  same  with  either  artificial 
or  natural  upper  teeth.  The  lower  bite-plate  is  formed  and  trimmed 
to  occlude  evenly  with  the  upper  teeth,  and  of  such  length  that  the  dis- 
tance between  the  jaws  as  determined  by  the  appearance  of  the  patient 
is  correct.  The  bite-plate  is  given  a  layer  of  wax  over  its  occlusal 
surface  and  the  bite  taken  in  the  usual  way.  Where  there  is  an  artificial 
denture  for  the  upper  jaw,  it  is  well  to  remove  this  with  the  bite,  to 
mount  it  upon  the  articulator,  and  to  articulate  the  lower  teeth  to  it 
rather  than  to  a  cast  formed  from  the  tooth  depressions  in  the  wax. 
\Yhere  the  denture  has  been  made  some  time  before  the  lower  teeth 
were  lost,  and  particularly  where  the  teeth  are  set  at  irregular  le^'els  to 
occlude  with  the  natural  ones,  it  is  advisable  to  reset  them  with  the  lower 
teeth,  as  a  much  more  satisfactory  occlusion  may  be  obtained. 

Bite-plates  for  Temporary  Dentures. — These  dift'er  in  no  wise  from 
the  plates  already  described,  except  that  they  do  not  extend  over  the 
labial  surface  of  the  cast,  this  being  more  especially  true  of  those  for  the 
upper  jaw.  This  arrangement  is,  of  course,  necessitated  by  consid- 
erations of  contour.  They  are,  in  consequence,  more  difficult  of  re- 
tention, and  this  must  be  looked  out  for  and  pro^•ided  for  by  means 
already  discussed. 

Bite-plates  for  Partial  Dentures. — Except  in  those  cases  in  which 
only  a  few  teeth  have  been  lost,  bite-plates  must  be  constructed  for  tak- 
ing the  bite  for  partial  dentures.  In  general  it  is  better  to  construct 
them  of  a  thin  sheet  of  modelling  compound  rolled  out  to  about  the 
thickness  of  Xo.  12  gauge,  adapted  to  the  cast,  and  trimmed  to  the  plate 
outline.  Vacancies  between  the  teeth  are  built  up  with  additions  of 
modelling  compound  to  the  level  of  the  adjacent  teeth  at  such  places  as 
it  is  necessary  that  the  plate  should  oppose  a  tooth  in  the  opposite  jaw 


352 


DATA   TO  BE   USED  IN  CONSTRUCTING  DENTURES. 


and  stay  the  bite.  (Figs.  323  and  324.)  Where  the  natural  teeth 
remaining  occlude  and  stop  the  closure  at  that  point,  these  spaces  on 
the  partial  bite-plate  may  be  built  up  with  soft  wax  just  before  the 
closure  for  fixing  the  bite  is  made,  the  soft  wax  receiving  an  impression 
of  the  opposite  teeth. 

Partial  bite-plates  may  often  be  strengthened  to  advantage  by  im- 
bedding iron  or  brass  wire  of  proper  shape  in  them  at  such  places  as 
will  be  exposed  to  strain,  anrl  this  is  particularly  true  of  partial  lower 
j)latcs. 

Taking  the  Bite  in  Partial  Cases. — (1)  In  the  construction  of  den- 
tures for  jjartial  cases  where  the  remaining  natural  teeth  occlude  prop- 


FiG.  324 


Bite-plate  for  partial  lower  denture. 


Bite-plate  for  partial  upper  denture. 


erly  and  particularly  if  only  a  few  have  been  lost,  it  is  only  necessary  to 
be  assured  that  the  teeth  of  the  casts  occlude  in  the  same  way  that  the 
natural  teeth  do,  and,  if  there  are  enough  points  of  bearing,  occasionally 
they  may  be  mounted  on  the  articulator  without  taking  the  bite.  If,  how- 
ever, a  roll  of  soft  yellow  wax  is  placed  between  the  patient's  teeth  and 
they  are  brought  to  the  position  of  natural  occlusion,  the  wax  may  be 
pressed  up  with  the  fingers,  cooled  with  water,  removed  from  the  mouth, 
and  the  casts  may  be  fitted  into  the  wax  with  the  assurance  that  their 
relation  is  correct.  It  is  important  to  be  certain  that  the  teeth  come  into 
the  po.sition  of  correct  occlu.sion  when  the  jaws  are  closed  upon  the  wax, 
and  it  is  expedient  to  mark  oppo.site  points  with  a  lead  pencil  upon  the 
external  surface  of  two  teeth  that  occlude,  and  to  observe  if  these 
bear  the  same  relation  when  the  jaws  are  closed  for  the  bite.  This 
includes  partial  upper  or  partial  lower  dentures  or  both. 

(2).  Where  the  teeth  remaining  do  not  occlude,  as  in  the  case  of  a  par- 
tial upper  and  partial  lower  denture,  it  is,  of  course,  necessary  to  have  bite- 
plates  to  establish  the  distance  between  the  jaws,  as  was  done  with  the 
full  upper  and  lower.  These  are  trimmed  tentatively  to  correspond  in  the 
length  of  their  occluding  portions  with  the  adjacent  teeth  and  are  tried 
in  the  mouth.  The  same  general  principles  which  determine  the 
length  of  the  full  upper  and  lower  bite-plates  must  be  borne  in  mindi 


A  R  T/CULA  TORS.  353 

but  the  lengtli  of  the  remaining  natural  teeth  will  be  the  main  guide  in 
determining  the  trimming.  The  plates  and  teeth  should  occlude  with 
the  same  evenness  and  firmness  which  is  demanded  of  the  full  plates, 
each  tooth  striking  upon  the  bite-plate.  The  plates  are  removed, 
wiped  dry,  and  their  occlusal  surfaces  covered  with  softened  wax,  and  the 
bite  taken  as  has  been  before  described.  With  a  full  denture  for  one  jaw 
and  partial  for  the  other,  as  in  a  case  in  which  some  of  the  lower  nat- 
ural teeth  remain,  the  obvious  method  is  to  combine  the  principles  of 
bite  taking  for  partial  and  for  full  dentures,  being  guided  by  the  nat- 
ural teeth  as  to  the  length  of  the  bite-plate,  by  the  external  appearance 
of  the  patient  as  to  the  contour  and  the  distance  between  the  jaws. 

(3).  There  are  occasional  cases  requiring  partial  upper  or  lower 
dentures  or  both  where  the  remaining  natural  teeth  occlude,  but  where 
they  are  either  much  abraded  or  have  been  driven  out  of  their  places  by 
the  force  of  occlusion,  and  the  distance  between  the  jaw^s  which  they 
establish  is  insufficient.  It  is  usually  ad^^sable  in  such  instances  to 
"open  the  bite."  The  bite-plates  are  trimmed  to  a  length  in  accordance 
with  the  amount  it  has  been  determined  the  jaws  are  to  be  separated, 
and  the  procedure  is  the  same  as  where  there  were  no  points  of  oc- 
clusion. It  must  be  borne  in  mind  that  the  natural  teeth  separated  by 
this  measure  should  be  built  up  by  operative  measures  or  by  crowning, 
if  possible,  as  they  cannot  otherwise  participate  in  the  masticatory 
functions  of  the  denture.  Instances  demanding  this  proceedure  are 
not  of  frequent  occurrence,  buta  few  cases  are  much  simplified  and  the 
mouths  much  improved  by  thus  establishing  a  new  position  of  occlusion. 

The  determination  of  the  relation  of  the  jaws  to  the  temporo-maxil- 
lary  articulations,  and  the  determination  of  the  path  of  the  condyle  in 
its  forward  and  lateral  excursions  are  questions  so  closely  related  to  the 
subject  of  articulators  that  it  will  be  necessary  to  consider  them  con- 
jointly. 


ARTICULATORS. 

As  originally  designed  the  instrument  known  as  the  articulator  was 
simply  intended  as  a  means  of  maintaining  the  plaster  casts  in  the  posi- 
tion of  occlusion  during  the  operation  of  arranging  and  mounting  the 
artificial  teeth.  -The  bite  having  been  taken,  the  casts  were  arranged  in 
the  occlusal  position  and  attached  to  the  metal  frames  of  the  instrument, 
and  thus  their  occlusal  relation  was  preserved  while  the  teeth  were  being 
set.  In  its  simplest  form  the  instrument  consists  of  two  frames  joined 
by  a  hinge,  which  permits  the  separation  of  the  casts  without  detaching 
them  from  the  articulator.  The  invention  of  the  device  is  attributed  to 
J.  B.  Gariot  about  1805.^  Many  forms  of  articulators  constructed 
upon  a  similar  principle  have  been  used  since  that  time,  a  common 
type  in  use  at  the  present  day  being  illustrated  in  Fig.  325. 

Except  for  convenience  in  handling  while  the  teeth  are  being  mounted, 

1  Guerini:  The  Historical  Development  of  Dental  Art.     The  Dental  Cosmos,  vol.  xliii.,  p.  8. 
23 


354 


DATA    TO  BE   USED  IN  CONSTRUCTISG   DESTniES. 


the  occlusal  relations  of  the  casts  may  be  j)reser\'e<l  in  as  satisfactory  a 
manner  by  an  extension  of  their  posterior  jjortions  with  plaster  to  form 
a  point  of  bearinfj  between  them.  An  extension  of  one  of  the  easts  is 
made  with  i)laster,  the  upper  surface  being  made  fiat  and  haxing  several 
well-defined  depressions  without  undercut  made  in  it,  and  it  is  then  var- 
nished. The  other  cast  hax'in";  l)een  ])laced  in  the  proper  relation,  its 
distal  surface  is  similarly  extended,  the  added  plaster  flowing  o\er  the 
^•arnished  surface  and  establishing  a  bearing  between  them. 

The  hinge  articulator  is  not  intended  as  a  means  of  imitating  the 
masticatory  movements  of  the  jaw.  As  a  rule,  no  attention  is  paid 
in  mounting  the  casts  upon  it  to  see  that  they  are  related  to  the  hinge 
joint  as  the  jaws  are  to  the  temporo-mandibular  articulation,  nor,  in- 
deed, does  the  former  resemble  the  mechanism  of  the  latter  in  an\'  wa\'. 


Fig.  325 


Scl  scrcii^"'^^ 


Vpper  plate 


Hintjt 


Plain  line  articulator. 


The  mandible  moves  approximatel>-  in  the  arc  of  a  circle  in  its  depres- 
sion and  elevation  (see  Chapter  IV.),  but  the  centre  about  which  this 
occurs  is  not  in  the  condyle  except  at  the  beginning  of  the  depression, 
and  no  simple  hinge  could  imitate  it.  The  casts  mounted  upon  a  simple 
hinge  articulator,  therefore,  occupy  the  positions  occupied  by  the 
iaws  onlv  when  the  casts  are  in  the  occlusal  relation,  and  the  joint  of  the 

•  •  •  1 

articulator  serves  solely  for  convenience  m  separating  the  casts. 

This  form  of  articulator  has  a  distinct  field  of  usefulness,  but  its 
boundaries  are  prescribed.  In  those  cases  in  which  a  number  of  the 
natural  teeth  remain  in  the  mouth,  as  in  partial  dentures,  or  full  upper 
or  lower,  where  most  of  the  opposing  series  arc  natural  teeth,  this  in- 
strument may  be  used  with  satisfaction.  In  these  several  instances 
the  forms  of  the  morsal  surfaces  of  the  artificial  teeth  are  determined  by 
those  of  their  opponents  of  the  natural  series,  which  latter  serve  as  a 


A  R  TICULA  TORS.  355 

safe  index  of  tlie  forms  best  adapted  for  masticatory  purposes  for  the 
eases  in  question. 

No  type  of  this  articuhxtor  should  be  used  which  is  not  sufficiently 
accurately  ma(ie  to  avoid  lateral  mo\'ement  at  the  joint.  This  mechan- 
ical defect  may  alter  the  relation  of  the  casts  in  the  occlusal  position  and 
the  dentures  will  l)e  correspondingly  inaccurate.  It  must  also  be  noted 
that  the  frec^uent  practice  of  attempting  to  correct  defects  in  the  vertical 
relations  of  the  casts  originating  from  an  inaccurate  bite,  by  raising  or 
lowering  the  upper  portion  of  the  articulator,  as  the  bite  is  found  to 
be  too  short  or  too  long,  is  to  be  decried  because  the  relation  thus 
established  between  the  casts  cannot  be  that  e^•er  existing  between 
the  jaws. 

In  the  use  of  this  instrument  the  casts  are  placed  in  their  proper 
positions  in  the  bite-plates,  having  been  trimmed  so  that  they  may  be 
accommodated  between  the  jaws  of  the  articulator.  x\s  they  are  to  be 
attached  by  means  of  plaster,  and,  as  after  this  has  set  and  dried  out  it 
becomes  so  hard  that  there  is  danger  of  fracture  to  the  casts  when  they 
are  removed,  it  is  advisable  to  coat  the  bases  of  the  casts  with  sandarac 
varnish,  with  the  exception  of  a  small  area  about  the  size  of  a  twenty- 
five-cent  piece  in  the  centre  of  this  surface.  The  casts  are  wet  and  a 
plaster  batter  used  to  attach  them  to  the  articulator,  the  union  obtained 
from  the  small  unvarnished  area  being  sufficient  to  hold  them  in  place, 
and  yet  they  may  be  removed  without  difficulty  after  the  teeth  are 
set  up. 

The  first  instrument  in  which  an  attempt  was  made  to  imitate  the 
temporo-mandibular  joint  with  the  joint  mechanism  of  the  articulator 
and  thus  to  permit  a  reproduction  of  the  masticatory  mo^'ements  of  the 
mandible  was  that  of  W.  G.  A.  Bonwill.  It  was  designed  by  him  in 
1858,  and  its  well-known  form  is  shown  in  Fig.  326.  With  this  apparatus 
an  effort  was  made  to  imitate  the  movements  of  the  mandible  occurring 
in  its  forward  and  lateral  excursion,  as  well  as  in  its  depression.  The 
joint  mechanism  consists  of  a  ring  sliding  upon  a  bar,  in  imitation  of 
the  sliding  movement  of  the  condyle,  the  direction  of  the  bar  deter- 
mining the  path  pursued  by  the  lower  cast.  The  ring  is  attached, 
however,  to  the  portion  of  the  articulator  carrying  the  upper  cast, 
the  bar  being  a  part  of  that  carrying  the  lower.  So  long  as  the  upper 
and  lower  loops  of  the  instrument  are  parallel,  the  path  of  the  condyle 
as  represented  by  the  bar  is  parallel  to  them,  and  hence  in  a  horizontal 
direction;  but  as  the  portion  carrying  the  lower  cast  is  depressed,  rotat- 
ing about  a  horizontal  axis  passing  through  the  rings,  the  bar,  being 
a  portion  of  this,  is  correspondingly  elevated,  its  angle  with  the  horizontal 
plane  is  changed,  and  the  path  of  the  condyle  is  represented  as  de- 
scending, the  angle  which  it  makes  with  the  horizontal  being  determined 
by  the  amount  of  depression  of  the  lower  portion  of  the  instrument. 
This  is  a  faulty  principle,  and  the  instrument  does  not  accurately  repre- 
sent the  movement  of  the  jaw.  It  was  shown  in  Chapter  IV.  that 
the  path  of  the  condyle  is  downward  and  forward,  that  it  is  rarely 
horizontal,  and  although  the  paths  differ  in  different  individuals,  an 


356  DATA   TO  BE   USED  IN  CONSTRUCTING   DENTURES. 

instrument  representing  the  condyle  path  by  a  bar,  the  inclination  of 
which  is  changed  as  the  jaw  is  depressed,  cannot  correctly  imitate  the 
mandibular  movement. 

The  instrument  represents  the  condyles  as  four  inches  from  the 
centre  of  one  to  that  of  the  other,  and  it  is  directed  that  the  casts  should 
be  placed  upon  the  articulator  with  their  general  alveolar  planes 
parallel  to  the  loops  to  which  they  are  attached,  the  centre  of  the  lower 
alveolar  ridge  in  front  being  located  four  inches  from  each  of  the  rings 
representing  the  condyles.  This  presupposes  a  uniform  intercondylar 
distance  of  four  inches,  and  a  like  distance  between  the  centre  of  each 
condyle  and  the  lower  alveolar  ridge,  conditions  which  do  not  obtain  in 

Fig.  326 


Bonwill  articulator.     (Photograph  of    instrument  in  collection  of    the  Department  of    Dentistry, 

University  of  Pennsylvania.) 

the  natural  jaw.  Cryer^  has  called  attention  to  the  difference  in  inter- 
condylar distance  in  two  mandibles  in  his  possession:  furthermore, 
such  uniformity  in  the  dimensions  of  the  jaws  of  different  individuals 
is  not  in  accord  with  actual  anatomy.  The  instrument,  besides  being 
constructed  upon  a  faulty  principle,  is  not  adjustable  in  any  way  to 
the  individual  case,  and  represents  the  ideal  of  the  designer.  The 
principles  of  tooth  articulation,  however,  enunciated  b>-  Dr.  Bon- 
will in  connection  with  this  articulator  are  extremely  valuable,  and  will 
be  discussed  in  a  later  chapter. 

Various  efforts  have  been  made  to  reproduce  the  movements  of  the 
lower  jaw  by  means  of  an  instrument.     The  articulator  designed  by 

>  Internal  Anatomy  of  the  Face. 


ARTICULATORS. 


357 


W.  E.  Walker,!  illustrated  in  Fig.  327,  was  an  improvement  upon  the 
Bonwill  articulator,  in  that  the  bar  determining  the  path  of  the  condyle 
is  adjustable  to  any  angle.     By  means  of  a  "facial  clinometer,"  to  be 


Fia.  327 


Walker's  articulator. 


used  in  connection  with  the  instrument,  the  angles  made  by  the  paths 
of  the  two  condyles  with  the  general  alveolar  plane  are  determined 
for  each  patient  and  the  articulator  is  set  to  correspond  therewith. 


Fig.  328 


The  Gritman  articulator. 

It  is  a  somewhat  complicated  apparatus  and  has  never  come  into  general 


use. 


The  Gritman  articulator'-  (Fig.  328)  represents  the  path  of  the  con- 

1  Facial  line  and  angles  in  prosthetic  dentistry.     The  Dental  Cosmos,  vol.  xxxix.,  p.  789. 
!  Introduced  in  1899. 


358 


nATA  TO  UK  rsh'i)  jy  constuuctjm;  dicstcres. 


dyle  as  a  strai^dit  line  niakiiit;  an  an^^le  with  the  ^^eneral  alveolar  plane 
which  the  designer  obtained  as  an  average  hy  the  measurement  of  a 
large  number  of  skulls.  The  superior  mechanical  construction  and 
coinenience  of  this  instrument  have  recommended  its  use  to  many, 
but  it  is  not  capable  of  adjustment  to  the  exact  requirements  of  the 


Fig.  .'529 


Christensen'a  articulator. 


individual  case.  The  articulator  of  Christensen^  (Fig.  329)  is  capable 
of  adjustment  in  the  matter  of  the  direction  of  its  condyle  paths.  The 
New  Century  articulator^  (Fig.  330),  designed  by  George  B.  Snow,  has 
the  mechanical  excellence  of  the  Gritman  articulator  and,  in  addition, 


Fig.  330 


New  Centun,-  articulator,  designed  by  George  B.  Snow. 

has  adjustable  condyle  paths.  In  common  with  all  anatomical  articula- 
tors so  tar  described,  it  is  constructed  on  a  plan  of  a  constant  inter- 
condylar distance  of  4  inches  and  is  not  adjustable  in  this  particular. 

1  Ash's  Quarterly  Circular,  December,  1901,  p.  409. 

2  Introduced  in  1907. 


ARTICULATORS. 


3o9 


For  li't'iitTal  use  in  the  lab()ratt)ry  it  will  be  found  an  instrument  of 
sufficient  precision  for  all  practical  purposes. 

While  the  fact  that  the  path  of  the  condyle  is  not  a  straight  line  has 
been  proved  by  the  work  of  various  investigators,  notabl}'  J.  B.  Parfit,' 
George  C.  Campion,'  Thos.  E.  Constant,^  it  has  been  represented  as 
such  in  all  the  instruments  so  far  discussed.  The  articulator  of  J.  B. 
Parfit  represents  the  path  as  curved,  and  pieces  of  metal  plate,  having 
l)een  cut  out  to  correspond  with  the  ascertained  paths  of  the  case  in 
hand,  are  clamped  to  the  frame  of  his  articulator.  Inasmuch  as  the 
paths  of  movement  of  the  condyle  while  the  teeth  are  in  contact  are 
the  only  ones  with  wdiich  wt  are  concerned  in  the  articulation  of  artificial 
teeth,  and  as  this  contact  is  maintained  only  in  the  movement  of  the 
condyle  from  its  most  distal  position  to  a  point  somewhat  short  of  the 
summit  of  the  eminentia  articularis,  during  which  time  the  condyle 

Fig.  331 


Articulator  of  Gysi. 


moves  nearly  in  a  straight  line,  for  most  practical  purposes  in  tooth 
articulation  it  may  be  represented  as  such  in  the  articulator. 

The  articulator  of  Gysi  (Fig.  331)  is  the  most  accurate  device  so  far 
designed  as  a  mechanical  representation  of  the  temporo-mandibular 
joint.     The  following  is  a  description  of  the  instrument:* 

"This  articulator  (see  Fig.  331),  like  all  others,  consists  of  a  mov- 
able upper  part  (Fig.  331,  0),  and  a  fixed  lower  part,  u.  To  the  upper 
part  the  straight  bow  (Fig.  340,  O),  is  attached  and  secured  by  screws,  S. 
An  extra  bayonet-shaped  bow  (Fig.  331,  o)  can  be  inserted  as  in  Fig. 
331,  o,  or  inverted  to  correspondingly  suit  the  height  of  the  plaster 

'  A  new  anatomical  articulator.  Transactions  Odontological  Society  of  Great  Britain,  1903, 
p.  337. 

-  Method  of  recording  graphically  the  movements  of  the  mandibular  condyles  in  the  li\dng  suD- 
ject,  The  Dental  Digest,  1903,  p.  841. 

5  The  movements  of  the  mandible:  Brit.  Jour.  Dent.  Science,  1901,  p.  807. 

■"  The  Dental  Cosmos,  vol.  lii.,  p.  148. 


360  DATA    TO  BE   USED  IN  CONSTRUCTING   DENTURES. 

models.  To  the  lower  part  a  straifjht  bow  is  attached  and  secured  by 
screws,  S.  An  extra  bow  can  l)e  attached  ha^'ing  a  base  that  is  H  ccm. 
higher.  With  these  four  bows  six  diilerent  combinations  can  be 
effected  to  correspond  to  the  height  of  the  plaster  models,  thus  saving 
much  time  in  their  preparation  for  the  articulator.  The  bows  should 
be  oiled  and  pushed  as  far  into  the  articulator  as  they  will  go,  so  that 
should  it  l)e  necessary  for  any  reason  to  remove  them,  together  with  the 
models  from  the  articulator,  they  can  be  easily  and  accurately  placed 
in  their  former  positions. 

"To  the  upper  bow  an  adjustable  supporting  ])in,  St,  is  attached, 
which  rests  on  the  narrow  end  of  the  small  plate.  T,  of  the  lower  bow. 
On  this  narrow  end  of  the  lower  bow  is  attached  an  inclined  plane,  E, 
on  which  the  su}3porting  pin  moves  upward  in  the  side  movements. 
The  supporting  pin  should  always  rest  at  the  foot  of  this  inclined 
plane.  This  inclined  plane  forms  the  incisor  guide,  and  serves  on  the 
articulator  as  a  substitute  for  the  overbite.  I'p  to  the  present  the 
artificial  incisors,  attached  with  wax  to  the  trial  plates,  have  taken 
the  place  of  this  incisor  guide.  This  was  a  most  uncertain  guide, 
especially  in  warm  weather.  For  practical  reasons,  which  will  not  be 
further  discussed,  this  inclined  plane  is  attached  to  the  lower  part 
of  the  articulator  instead  of  to  the  upper  part,  just  as  all  articulators 
have  a  fixed  lower  and  a  movable  upper  part,  entirely  contrary  to  the 
natural  relations,  but,  as  is  well  known,  answering  the  same  purpose. 

"As  the  supporting  pin  acts  as  a  guide  to  the  height  of  the  bite,  it 
is  placed  in  front  of  the  incisors,  because  it  is  only  here  that  a  true 
and  secure  support  can  be  obtained.  If  this  supporting  pin  interferes 
with  the  setting  up  of  the  incisors,  it  can  be  removed  until  the  latter  are 
placed  in  position. 

"File-marks  (Fig.  331,  F)  can  be  made  on  the  supporting  pin,  so 
that  there  is  at  all  times  a  guide  to  show  that  the  height  of  the  bite  has 
not  been  changed  in  the  setting  up  of  the  teeth. 

"The  placing  of  this  supporting  pin  in  front  of  the  incisors  offers  the 
further  advantage  that  the  articulator  is  quite  unobstructed  at  the 
back,  so  that  the  lingual  surfaces  of  the  teeth  arc  clearly  visible  and  can 
easily  be  reached  with  the  fingers  and  wax  sj)atula.  This  is  important, 
in  that  it  permits  of  the  correct  articulation  of  the  lingual  surfaces  of 
the  teeth. 

"The  most  important  function  of  this  supporting  pin  and  the  in- 
clined plane  consists  in  the  prevention  of  the  wrong  downward  move- 
ment of  the  upper  part  of  the  articulator  produced  in  all  articulators  up 
to  this  time  when  reproducing  lateral  movements. 

"The  upper  bow,  O,  is  connected  with  the  upper  part  of  the  articula- 
tor by  a  hinge  joint,  so  that  in  the  setting  up  of  the  artificial  teeth  open- 
ing and  closing  movements  can  be  made  that  are  independent  of  the 
true  joint  movement:  consequently  the  two  condyle  parts  of  the 
triangle  can  be  combined  exactly  and  precisely  with  the  incisive  part 
of  the  triangle  in  such  a  way  that  all  unnatural  movements  are  impos- 
sible.    In  this  manner  the  downward  movement  of  the  mandible  com- 


ARTICULATORS.  361 

bines  with  the  forward  movement  in  the  direct  forward  and  lateral 
mo^•ements.  This  combined  movement,  which  has  long  been  recog- 
nized, is  for  the  first  time  accurately  reproduced  by  the  articulator. 
The  importance  of  this  fact  is  fully  explained  in  another  chapter. 

"The  upper  and  lower  parts  of  the  articulator  are  connected  through 
the  real  joint,  G,  which  permits  of  the  lateral  movements.  Two  springs, 
F,  automatically  bring  the  two  parts  back  to  their  normal  positions. 

"  The  joint  is  formed  by  the  fork  (g)  of  the  lower  part  of  the  articula- 
tor, the  prongs  of  which  pass  through  the  E-shaped  part  of  the  upper 
half  and  receive  the  slotted  plate,  Sp.  The  fork  (g)  rotates,  and  with 
the  slotted  plate  can  be  fixed  bv  the  screw  (5)  at  an  angle  of  from  0°  to 
50°. 

"The  two  identical  slots  in  the  slotted  plate  which  receive  the  prongs 
of  the  fork  (g)  correspond  in  form  to  the  path  which  the  condyles  take  in 
their  movements  during  mastication. 

"To  be  quite  exact,  a  number  of  different  forms  of  slotted  plates 
should  be  kept.  From  my  long  experience,  however,  I  have  found  that 
the  two  average  forms  are  quite  sufficient,  and  if  the  artificial  teeth  are 
placed  in  the  exact  position  necessary  to  secure  the  full  value  of  the 
gradations  of  these  tw^o  condyle  path  forms,  the  result  is  most  satis- 
factory. If  a  special  form  for  every  case  is  thought  necessary,  as 
advocated  by  Campion  and  Parfit,  it  can  be  easily  and  quickly  sawed 
out  of  thin  brass  plate  and  placed  on  the  articulator. 

"The  pin,  st,  found  on  the  slotted  plate,  serves  to  bring  the  latter  into 
its  proper  place,  and  should  always  be  placed  in  the  hole  provided  for  it 
in  the  middle  of  the  E-shaped  joint. 

"In  order  to  change  the  slotted  plate,  the  binding  screw,  5,  is  first 
loosened,  then  the  prongs  of  the  fork  g  are  turned  to  a  vertical  position, 
which  will  allow  the  plate  to  slide  over  the  head  of  the  binding  screw. 
With  the  prongs  in  the  same  position  another  plate  can  be  put  on  and 
fixed  at  the  desired  angle.  This  is  accomplished  by  placing  the  index 
of  the  slotted  plate  at  the  required  degree  on  the  engraved  scale,  W, 
in  the  E-shaped  joint. 

"When  making  full  upper  and  lower  dentures  \\dthout  measuring  the 
individual  condyle  paths,  the  index  of  the  slotted  plate  should  be  placed 
at  the  average  angle  of  30°.  It  is  not  absolutely  necessary  to  measure 
the  condyle  path  for  partial  dentures.  In  such  work  the  slotted  plate 
can  also  be  set  at  the  average  angle  of  30°.  In  this  way,  in  extreme  cases 
there  can  only  be  a  difference  of  20°  above  or  below  this  average  slant, 
which  is  not  much  when  we  consider  that  in  using  a  Bonwill  articulator 
there  can  be  a  difference  of  45°. 

"The  two  small  supporting  pins,  D  D,  at  the  back,  with  the  large 
supporting  pin,  St,  form  a  secure  triangle  which  is  not  to  be  found  in 
any  other  articulator.  This,  together  with  the  solid  cast  pieces,  pre- 
vents any  looseness  or  any  springiness,  and  thus  insures  the  possibility 
of  true  and  exact  work. 

"The  small  supporting  pins,  D  D,  in  the  slotted  upper  part,  0,  can 
be  moved  sideways.     They  rest  on  the  transverse  piece  of  the  lower 


362  DATA    TO  BE    USED   IS   CVySTIiUCIIMJ   DENTURES. 

part,  on  wliich  is  an  eiitiravcd  scale  to  iiKllcate  the  positions  of  the  pins. 
As  the  positions  of  these  sni)pt)rtin<i;  i)ins  are  determined  hy  the  ineisor 
path,  these  scales  are  only  of  value  when  two  or  more  full  upper  and 
lower  dentures  are  to  be  made  at  the  same  time,  when  the  tlilVerent 
positions  of  these  pins  can  l)e  noti-d  on  the  plaster  models." 

THE  RELATION  OF  THE  JAWS  TO  THE  TEMPORO-MANDIBULAR 

ARTICULATION. 

It  nuist  be  evident  that  in  an  articulator  in  which  the  mandibular 
movements  are  to  be  imitated  the  casts  must  occupy  the  same  position 
relative  to  the  joint  mechanism  as  the  jaws  occupy  relative  to  the 
temporo-mandibular  joint.  Otherwise  the  joint  mechanism  would  per- 
mit the  casts  to  be  moved  relatively  to  each  other  in  ways  in  which  the 
jaws  cannot  be.     A  means  of  determining  this  with  greater  or  less  pre- 


HI 

— a— 

i 
»-l- 

r 1  ^ 

4^ 

•^                                                              1, 

Snow  face-bow,  showing  bow  with  projecting  end  pieces  for  placing  over  the  condyles  and  clamp  for 
attaching  stem.     Also  stem  with  semicircular  plate  for  imbedding  in  bite-plate. 

cision  is  furnished  in  the  Snow  face-bow  which  is  designed  for  use  in 
conjunction  with  the  Gritman  articulator,  but  more  recently  with  the 
Xew^  Century  articulator.  It  is  illustrated  in  Fig.  332  and  consists  of 
a  stem  with  a  semicircular  i)late  attached  for  imbedding  in  the  bite- 
plate,  and  a  bow  with  a  clam]:)ing  device  and  projecting  inde.x  rods 
at  each  end  of  the  bow.  The  method  of  use  of  the  appliance  is  as 
follows:  After  the  bite  has  been  taken  and  the  bite-plates  are  firmly 
fixed  together  with  the  jaws  in  the  occlusal  relation,  the  plates  are  re- 
moved from  the  mouth,  and  the  casts  phT^ed  in  them  to  prevent  a  dis- 
tortion of  their  shape  in  subsequent  manipulations.  Then  the  semi- 
circular plate  of  the  stem  is  heated  sufficiently  to  allow  it  to  be  imbec^ded 


TIIK   TEMPOnO-MA  XDIB I  'LA  R  A  RTICULA  TION. 


363 


ill  the  uppcT  hitc-plate  (Fig.  'X\'.\),  \\\v  stem  ()ccui)yiiii;-  the  median  plane 
of  the  })hite.  Care  should  be  taken  to  see  that  the  high  lip  line,  the 
median  line,  and  the  lower  edge  of  the  bite-plate,  whieh  are  to  serve  for 
referenee  in  setting  the  teeth,  are  not  disturbed  by  this  procedure,  and 


Fig.  333 


Stem  with  semicircular  plate  imbedded  in  upper  bite-plate:  ready  to  be  returned  to  patient's  mouth. 

also  that  the  plates  themselves  are  not  distorted  in  form  or  relation. 
The  position  of  the  external  end  of  both  condyles  while  the  mandible 
is  in  its  most  distal  position  is  then  located  by  palpation  and  marked 
upon  the  skin  of  the  face  by  a  small 

piece  of  court  plaster  or  a  pencil  ^^°-  •^'^^ 

mark.  (Fig.  334.)  It  will  be  seen 
in  Fig.  220,  page  240,  that  the  ex- 
ternal end  of  the  condyle  is  one- 
half  inch  anterior  to  the  external 
auditory  meatus  and  just  below  a 
line  drawn  from  the  bottom  of  the 
meatus  to  the  anterior  nasal  spine. 
In  many  patients  the  end  of  the 
condyle  may  be  easily  felt  through 
the  tissues  covering  it ;  in  others  by 
placing  the  index-finger  just  inside 
the  external  auditory  meatus,  the 
thumb  on  the  surface  of  the  face 
just  anterior  to  the  position  of  the 
condyle,  then,  requesting  the  pa- 
tient to  open  and  close  the  mouth, 
the  location  is  determined. 

The  bite-plates  are  then  returned 
to  the  mouth  with  the  stem,  which 

is  now  attached  to  them,  projecting  between  the  lips.  The  bow  is  put 
in  place,  with  the  stem  entering  the  movable  clamp  which  slides  upon 
the  bow,  and  with  the  two  projecting  end  pieces  of  the  bow  accurately 
placed  over  the  condyles  as  indicated  by  the  pieces  of  court-plaster 
on  the  skin.     It  is  necessary  to  see  that  the  two  project  in  equal  amounts 


Patient  T\ith  the  external  end  of  the  head  of  the 
condyle  located  and  marked  on  the  skin. 


364 


DATA    TO  BE   USED  IN  COySTRUCTIXG  DENTURES. 


from  the  bow  before  the  milled  elamj)s  whieh  fix  them  are  tightened, 
because,  when  the  casts  are  to  be  mounted  on  the  articulator,  and  these 
end  pieces  are  pushed  completely  in,  the\'  just  reach  the  external  end 
of  the  joint  mechanism  of  the  articulator,  anil  this  precaution  is  neces- 
sary to  assure  a  centering  of  the  casts.  If  this  were  not  done,  that  is, 
if  the  two  end  pieces  project  unequal  amounts  when  the  bow  is  in  posi- 
tion on  the  face,  the  casts  will  not  be  centered  when  they  are  transferred 
to  the  articulator.  When  this  has  been  done,  the  movable  clamp,  which 
fixes  the  stem  to  the  bow,  is  tightened,  care  being  taken  that  the  pa- 
tient's jaws  are  firmly  closed  in  the  bite-plates,  and  that  the  end  pieces 

have  not  moved  from  their  posi- 
tions over  the  condyles.  (P  ig.  .'^35.) 
The  bow,  stem,  and  bite-plates, 
firmly  attached  together,  are  now  re- 
moved. The  casts  are  now  put  in 
position  in  the  bite-plates,  and  the 
projecting  end  pieces  are  pushed  as 
far  in  as  they  can  be,  and  the  milled 
nuts  turned  to  fix  them.  The  casts 
are  now  to  be  tried  upon  the  articu- 
lator with  the  holes  in  the  end 
pieces  fitting  over  the  projections 
upon  the  outer  side  of  the  joint 
mechanism.  After  the  casts  shall 
have  been  mounted  upon  the  Grit- 
man  articulator,  the  general  plane  of 
the  alveolar  ridge  of  the  cast  should 
be  as  nearly  parallel  with  the  upper 
bow  of  the  articulator,  as  it  may  be 
set  by  a  rotation  the  bow  and  casts 
attached  thereto  about  the  joints  of  the  articulator.  The  object  of  this  is 
that  this  plane  may  make  the  correct  angle  with  the  slot  in  the  articulator, 
which  determines  the  path  of  the  portion  corresponding  to  the  condyle. 
The  articulator  is  so  constructed  that  the  angle  formed  by  this  slot  and 
the  upper  bow  of  the  articulator,  corresponds  to  the  average  angle  formed 
by  the  path  of  the  condyle  and  the  plane  of  the  upper  alveolar  process 
in  a  large  number  of  cases  examined  by  its  designer.  If  the  upper  cast 
has  been  properly  formed  in  the  first  place  so  that  its  base  is  parallel  to 
the  general  alveolar  plane,  it  is  only  necessary  to  see  that  its  base  is 
parallel  to  the  upper  bow,  and  the  proper  angle  will  be  formed  between 
its  alveolar  plane  and  the  slot  at  the  joint.  The  screw  with  a  jam-nut, 
which  regulates  the  flistance  between  the  bows  of  the  articulator,  should 
be  screwed  tight  and  the  casts  may  be  trimmed,  if  this  is  necessary,  in 
order  that  they  may  be  accommodated  between  the  bows,  or  the  lower 
bow  may  be  separated  from  the  upper  by  sliding  it  downward  and  fixing 
it  at  the  proper  distance  by  means  of  thumb-screws  arranged  for  the 
purpose. 

When  the  Snow  face-bow  is  used  in  conjunction  with  the  Xew  Cen- 


]■„:.  :;:■!.-> 

'^^^pn 

1 

I^PI/ 

^l^^^^-^-^^^-^i^s:^ 

W    ^-'/     "" 

m     ^^ 

[  -.  -  ^^^^^^^^^^^^^^^^ 

i 

Patient  with  Snow  face-bow  in  place. 


THE  PATHS  OF  THE  CONDYLES.  36'5 

tury  articulator  or  any  other  with  adjustable  condyle  paths  with  which 
it  may  be  employed,  it  is  not  necessary  to  take  these  precautions  about 
havin^j  the  general  alveolar  plane  of  the  casts  parallel  with  the  bows  of 
the  articulator  for  the  reasons  above  mentioned,  because  the  condyle 
paths  are  subsequently  adjusted  to  the  proper  angle.  However,  as  a 
matter  of  convenient  positioning  of  the  casts  this  plan  will,  under  these 
circumstances,  be  found  advantageous. 

AVhen  the  casts  have  been  properly  adjusted  (Fig.  336),  they  are 
fixed  in  place  by  additions  of  plaster,  and  the  casts  are  ready  for  the 
subsequent  setting  of  the  teeth. 

The  Snow  face-bow  was  designed  for  use  with  the  Gritman  articulator, 
but  it  may  be  used  with  the  Walker  or  Christensen  articulator,  if  these 

Fig.  336 


Snow  face-bow. 


are  altered  slightly  by  the  addition  of  projections  at  their  joint-mechan- 
ism to  receive  the  projecting  ends  of  the  face-bow.  Since  the  ad^-ent 
of  the  New  Century  articulator,  with  which  it  may  be  very  conveniently 
employed,  the  results  obtained  in  tooth  articulation  by  the  use  of  this 
combination  of  instruments  have  been  most  satisf^^ng. 


THE   DETERMINATION    OF   THE   PATHS    OF   THE   CONDYLES 

It  was  shown  in  Chapter  TV.  that  in  the  typical  natural  dentures  there 
is  a  definite  relation  between  the  paths  pursued  by  the  condyles,  in  their 
forward  and  lateral  excursions,  and  the  forms  and  arrangement  of  the 
occlusal  surfaces  of  the  teeth,  and  that  during  the  sliding  contact  of  the 
teeth  the  path  pursued  by  the  mandible  is  determined  by  the  teeth  on  its 
anterior  extremity  and  the  condyles  and  glenoid  fossae  posteriorly.  In 
the  articulation  of  artificial  teeth,  it  is  desirable  that  they  should  be 
arranged  in  such  a  way  that  the  sliding  contact  may  be  possible  during 
their  use.  In  order  to  accomplish  this,  it  is  necessary,  therefore,  that 
they  be  set  up  to  accord  with  the  paths  pursued  by  the  condyles  in  the 


366 


DATA    TO  BE   USED  IN  COySTHUCTIMJ  DESTURES. 


Fig.  337 


individual  case  re{|uiriii,ii:  tlioni.  Tiiis  drmaiuls  that  tlie  paths  of  the 
condyles  be  ascertained,  if  this  l)e  })ossihle,  and  that  an  articnUitor 
capable  of  imitating  these  movements  be  utilized  in  setting  the  teeth, 
and  that  it  be  set  to  imitate  the  condylar  paths  in  the  given  case.  No 
articulator  has  yet  been  constructed  which  is  exactly-  able  to  reproduce 
these  movements,  but  of  the  several  anatomical  articulators  already 
described,  all  possess  sufficient  accuracy  to  make  them  of  some  service, 
and  while  no  one  of  them  is  perfect,  the  use  of  them  greatly  impro\es 
the  results  in  the  articulation  of  the  artificial  teeth. 

Given  a  satisfactory  articulator,  it  then  becomes  necessary  to  have 
some  means  of  ascertaining  the  paths  i)ursued  by  the  condyles  of  the 
edentulous  jaw  for  which  the  denture  is  to  be  made.  These  must  then  be 
recorded  by  some  means,  and  the  record  transferred  to  the  articulator. 
This  is  a  somewhat  difficult  matter,  as  in  the  living  subject  the  condyles 

and  fossa^  are  beneath  the  skin, 
and  this  makes  it  im])ossible  to 
directly  observe  the  operation  of 
the  joint.  Campion^  has  devised 
a  means  of  accomplishing  this  by 
the  use  of  a  bow  carrying  two 
points ;  the  bow  is  attached  to  the 
teeth  of  the  lower  jaw,  and  the 
points  are  placed  over  the  exter- 
nal ends  of  the  condyles  pre- 
viously located.  The  points  carry 
a  pen  or  pencil,  and  the  position 
of  the  condyle  at  any  position  of 
the  lower  jaw  is  recorded  by  a 
mark  upon  the  skin  of  the  face 
and  the  record  may  then  be  trans- 
ferred to  a  piece  of  paper.  This 
method  is  chiefly  for  use  in  study- 
ing the  mo\ement  of  the  mandi- 
ble, and  is  not  designed  for  use  in 
the  setting  of  artificial  dentures. 
Walker  has,  however,  designed  a 
method  for  determining  the  condylar  path  on  each  side  independently, 
which  he  applied  in  the  construction  of  dentures.  He  used  a  com])li- 
cated  apparatus  which  he  called  a  "facial  clinometer,"  by  means  of 
which  the  angle  between  the  path  of  the  condyle  and  the  plane  of  the 
upper  alveolar  process  was  determined,  and  the  articulator  bearing  his 
name  set  according  to  this  for  the  case  under  consideration.  The  ap- 
paratus is  so  complicated  that  it  has  never  come  into  general  use. 

Christensen^  has  proposed  a  method  for  harmonizing  the  articulation 
of  the  teeth  with  the  mo^'ement  of  the  condyles.     His  methc^d  is  based 

'  Method  of  Recording  Graphipiilly  the  Movements  of  the  Mandibular  Condyles  in  the  Living 
Subject:  George  C.  Campion.     The  Dental  Digest,  1003,  p.  841. 

2  A  Rational  Articulator.  By  Carl  Christensen.  Quarterly  Circular  of  C.  Ash  &  Sons,  December, 
1901,  p.  409. 


I       I 


Schematic  drawing,  showing  relation  of  dentures 
in  position  of  occlusion  and  in  forward  po.sition  of 
mandible.      (Christensen.) 


THE  PATHS  OF  THE  CONDYLES. 


367 


upon  the  following-  facts,  to  which  he  calls  attention.  During  the 
movement  of  the  mandible  in  the  individual  with  natural  teeth,  while 
these  teeth  preserving  a  sliding  contact,  the  condyle  can  move  only 
from  its  distal  position  downward  and  forward  a  distance  of  4-5  mm., 
with  12  mm.  as  the  probable  maximum.  It  is  during  this  sliding  con- 
tact of  the  teeth  that  the  movements  of  the  condyle  occur  which  are 
important  from  the  standpoint  of  the  function  of  the  denture:  we  are 
only  concerned  \\\i\\  such  movements  of  the  condyle.  Therefore,  the 
path  of  the  condyle  would  be  a  curve  of  large  radius,  or,  for  all  practical 
purposes  in  tooth  articulation,  would  be  a  straight  line.  If  an  articulator 
C(Hild  be  set  so  that  the  parts  representing  the  paths  of  the  condyles 
would  be  either  identical  or  concentric  with  those  actually  pursued  by 
the  jaws,  the  teeth  could  be  set  up  according  to  this  and  would  articulate 
when  placed  in  the  mouth.  Christensen's  articulator  is  used  upon  this 
principle. 

The  bite  is  taken  in  the  ordinary  w^ay  and  the  casts  are  mounted 
upon  the  articulator  with  their  median  line  corresponding  to  the  centre 


Fig.  338 


Casts  mounted  on  Christensen  articulator,  in  position  of  occlusion.     (Christensen.) 

of  its  bows,  and  the  line  between  the  positions  of  the  lower  central  inci- 
sors, 10  cm.  from  each  joint,  representing  the  temporo-mandibular  joint. 
(Fig.  338.)  If  the  bite-plates  are  then  returned  to  the  mouth,  with  a 
small  lump  of  soft  wax  upon  the  occlusal  portion  of  the  upper  bite-plate, 
and  the  patient  is  instructed  to  throw  the  lower  jaw  forward  and  then 
to  bring  the  bite-plates  together,  a  record  is  made  of  the  jaws  in  this  posi- 
tion. (Fig.  337.)  If  the  casts  already  mounted  upon  the  articuhitor 
can  be  placed  in  the  bite-plates,  the  former  will  then  assume  the  position 
occupied  by  the  jaws,  and  if  they  were  originally  placed  upon  the  articu- 
lator in  the  same  relation  to  those  portions  of  it  representing  the  con- 
dyles, these  latter  must  now^  be  in  the  position  of  the  condyles  in  the 
forward  position  of  the  mandible.     The  path  of  the  condyles  to  this 


368 


DATA   TO  BE   USED  IN  CONSTBUCTING  DENTURES. 


point  is  approximately  a  straif^ht  line,  and  as  we  have  the  distal' end  of 
this  line  recorded  on  the  instrument  when  the  bite  was  taken,  we  now 
have  its  anterior  end  determined,  because  the  bow  of  the  articulator, 
like  the  mandible,  moves  as  a  whole.  If  the  portion  of  the  articulator, 
therefore,  which  represents  the  path  of  the  condyle  (the  bar  with  the 
spring  and  sliding  ring)  is  set  in  this  position  by  screws,  C  and  C  (Fig. 
339),  the  casts  may  then  only  be  moved  in  relation  to  each  other  as  the 
sliding  of  the  rings  on  the  bars  will  permit,  and  they  thus  imitate  the 
movements  of  which  the  jaw  is  capable. 

It  will  be  seen  at  once  that  this  imitation  of  the  jaw  movement  by  the 
articulator  cannot  be  mathematically  precise,  because  of  i)robable  errors 


Fig.  339 


Casts  arranged  in  forward  position  of  mandible  by  means  of  bite-plates;  articulator  adjusted  thereto. 

(Christensen.) 


in  the  record,  and  because  there  is  some  play  in  the  natural  joint  which 
no  articulator  can  ever  imitate.  It  is  sufhciently  accurate,  however, 
to  give  results  in  tooth  articulation  which  far  excel  those  obtained 
without  the  use  of  an  articulator  capable  of  indi^•idualizing  the  move- 
ments of  the  condyles. 

Since  the  publication  by  Gysi  of  the  results  of  his  work  along  the 
line  of  greater  accuracy  in  securing  these  various  records,  and  since 
the  publication  of  descriptions  of  his  instruments,  prosthetists  have  been 
provided  with  a  valuable  addition  to  their  armamentarium.  Especial 
attention  is  directed  in  the  following  quotation'  to  the  means  of  obtain- 
ing the  balancing  points  in  the  lateral  excursion  of  the  jaw,  the  first 
recorded  effort  to  adjust  the  articulator  to  a  varying  intercondylar 
distance. 

1  The  Problem  of  Articulation.  By  Alfred  Gysi.  The  Dental  Cosmos,  vol.  lii,  p.  1.  (Being  a 
translation  of  Professor  Gysi's  book,  "Beitrag  zum  Articulationsproblem,"  published  by  Hirschwald, 
Berlin,  in  190S,  with  some  practical  additions  written  since  its  publication. 


THE  UY8I  MEASURING  INSTRUMENTS. 


369 


THE    GYSI   MEASURING   INSTRUMENTS. 

"According  to  Bonwill,  the  two  condyles  form  an  equilateral  tri- 
angle with  the  contact  point  of  the  lower  central  incisors.  I  have,  there- 
fore, constructed  two  measuring  instruments.  With  the  one  (Fig.  .'540,  G) 
I  determine,  from  the  forward  and  opening  movements  and  the  combina- 
tion of  these  two,  the  form  and  direction  of  the  two  condyle  points  of 
the  triangle  in  a  vertical  plane;  with  the  other  instrument  (Fig.  340,  S) 
I  determine,  from  the  lateral  movements,  the  path  of  the  incisor  point 
of  the  triangle  in  a  horizontal  plane. 

"  From  the  registered  paths  of  these  three  points  of  the  triangle  in 
their  separate  directions,  I  can  direct  the  movement  of  the  mandible  in  all 
the  combinations  of  the  masticatory  movements. 


Pig.  340 


A,  Articulator;  O,  U,  extra  bows;  G,  condyle  path  register;  H,  horseshoe  plate;  Sch,  extra  pair  of 
condyle  path  guides;  W,  angle  measure  for  condyle  path  slant;  T,  type  plate  for  molar  groove;  S,  small 
register;  St,  holder  for  register  G  (to  be  used  when  plastering  models  to  articulator). 


"  The  Large  Registers  for  Determining  the  Slant  of  the  Condyle  Path. — 

This  instrument  (Fig.  340,  G)  serves  to  measure  the  path  taken  by  the 
condyles  in  the  movements  of  the  mandible.  The  important  part  of 
this  instrument  consists  of  two  lead  pencils,  which  in  every  individual 
case  can  be  placed  in  the  region  of  the  condyles  (Fig.  341). 

"  Its  attachment  to  the  mandible  is  accomplished  through"  the  horseshoe 
plate  (Fig.  340,  H),  which,  with  its  points  on  the  under  side,  is  pressed 
into  the  lower  wax  model  which  has  been  used  in  taking  the  bite  (Fig. 
343).  The  whole  is  so  well  balanced  and  weighted  that  it  will,  without 
any  further  help,  remain  iirmly  in  its  position  in  the  mouth. 

"Parallel  to  the  horseshoe  plate  (which  we  shall  consider  as  being  in 
place)  on  the  wax  model  and  on  a  line  with  the  plane  of  occlusion, 

24 


370 


DATA    TO  BE   USED  IN  CONSTRUCTING  DENTURES. 


parallel  ])lates  run  backward  on  both  sides  (Fig.  341,  P),  carrying  mov- 
able spring  lead  jjencils  in  the  region  of  the  joint  (Fig.  'M\,  B).  For 
extreme  cases  these  lead  pencil  holders  may  be  changed  from  the  left 
to  the  right  side,  or  moved  up  and  down  on  their  vertical  bars  with  a 
screw  (Fig.  340),  so  that  the  pencil  points  form  as  nearly  as  possible  a 
right  angle  to  the  writing  surface  of  the  recording  card  (Fig.  341). 
The  parallel  plates  with  the  lead  pencils  may  be  adjusted  for  individual 
cases  b^'  moving  the  plates  on  the  cross-bar  which  hokls  them  (Fig. 
341,  T)*. 

"This  instrument  also  serves  as  a  compass,  like  the  American  Snow 
face-bow,  w^hich  fixes  the  distance  of  the  plaster  models  in  correct  rela- 
tion to  the  axis  of  the  joint. 


Fig.  341 


Shows  the  method  of  detenniaing  the  slant  and  form  of  the  condj  le  path.      (Wilson,  after  Gysi.) 


"In  order  to  find  out  the  movements  of  the  mandible  in  different 
individuals,  the  wax  bite-plates  are  prepared  in  the  usual  manner,  except 
that  the  base  plates  must  be  either  of  modelling  compound,  1.5  mm.  in 
thickness,  or  of  some  other  equal  firm  material  reinforced  in  the  usual 
way  w^ith  a  piece  of  wire.  After  proper  attention  has  been  paid  to  all 
the  details,  such  as  securing  the  proper  fulness  of  the  wax  models  to 
insure  proper  lip  contour,  the  right  height  of  the  plane  of  occlusion,  the 
length  of  the  incisors,  the  median  line  of  the  face,  etc.,  the  patient  is 


THE  ay  SI  MEASURING  INSTRUMENTS. 


371 


Fig.  342 


directed  to  open  and  close  the  mouth  several  times,  during  which  the 
positions  of  the  condyles  are  ascertained  by  feeling  in  the  region  of  the 
ear  where  they  move.  Then  the  i)ositions  of  the  condyles  in  the  resting 
position  (with  the  moiith  closed)  are  found,  and  marked  on  the  surface 
of  the  skin  of  the  patient  with  a  pencil  or  with  chalk.  Usually  the  con- 
dyles are  found  about  1  cm.  in  front  of  the  tragus  of  the  ear,  in  the  direc- 
tion of  the  outside  corner  of  the  eye.  (Fig.  342.)  The  horseshoe  plate 
is  then  fastened  by  its  points  to  the  lower  wax  bite-plate  and  both  are 
placed  in  the  mouth. 

"  If  some  natural  teeth  are  left  in  the  mandible,  a  horseshoe  plate 
without  points  can  be  used.  Some  hot  modelling  compound  is  placed 
on  the  under  side  of  this  plate  and  pressed  over 
the  teeth,  just  as  though  an  impression  were  to 
be  taken.  In  most  cases  where  there  are  nat- 
ural teeth,  it  is  not  absolutely  necessary  to 
measure  the  relations  of  the  joints. 

"  The  condyle  path  register  is  now  attached 
to  the  horseshoe  plate,  which  in  its  position  in 
the  mouth  is  fixed  to  the  wax  bite-plate.  The 
lead  pencils  are  put  at  the  marked  places  which 
indicate  the  positions  of  the  condyles;  by  ad- 
justing them  on  their  perpendicular  bars  and 
through  the  sliding  arrangement  on  the  cross- 
bar, they  are  brought  close  to  the  surface  of 
the  skin. 

"The  form  and  slant  of  the  condyle  path 
will  then  be  found  by  inserting  a  piece  of  card- 
board, as  shown  in  Fig.  341,  between  the  pencil  points  and  the  skin  in 
the  region  of  the  joint,  with  the  lower  edge  parallel  to  the  parallel  plates 
of  the  register.  The  latter  plates  are  again  moved  on  the  cross-bar  until 
the  pencils  are  brought  in  such  close  contact  to  the  writing  surface  of 
the  card  that  the  springs  holding  the  lead  pencils  are  under  a  pressure. 
The  patient  is  directed  to  move  the  mandible  up  and  down,  and  from 
side  to  side  (chiefly  the  latter  motion),  until  the  condyle  path  is  clearly 
drawn  on  the  surface  of  the  recording  card.     (Fig.  341.) 

"The  lateral  movements  of  the  mandible  show  that  the  cur^-e  first 
made  by  the  opening  and  closing  movements  is  followed  in  the  lateral 
movements,  and  that  while  one  condyle  moves  forward,  the  other 
moves  more  or  less  backward.  (See  explanation  to  Fig.  348.)  The 
measuring  of  this  moving  path  of  the  mandible  occupies  hardlj'  three 
minutes'  time. 

"After  one  side  of  the  mandible  has  thus  been  measured,  the  same 
card  is  held  on  the  other  side,  and  the  same  procedure  is  again  followed. 
After  the  measuring  is  finished,  the  lead  pencils  are  moved  outward 
by  the  sliding  arrangement  on  the  cross-bar,  so  that  the  recording  card 
and  the  register  may  be  taken  away,  without,  however,  removing  the 
horseshoe  plate.  The  lead  pencils  with  their  holders  must  not  be 
moved  or  turned  on  their  vertical  bars,  as  their  position  is  of  importance 


372 


DATA    TO  BE   USED  IN  COySTEUCTING  DESTURES. 


ill  attaching  the  models  to  the  articiUator,  as  we  shall  see  later.     The 
wax  models  may  then  be  taken  from  the  mouth. 

"To  find  the  angle  of  the  registered  path  in  relation  to  the  occlusal 
plane,  a  slotted  plate  is  selected  which  corresponds  as  nearly  as  possible 
to  the  form  of  the  registered  path.  The  plate  chosen  is  placed  directly 
over  the  lead  pencil  drawing,  so  that  the  drawn  line  can  be  seen  ap- 


FiG.  343 


Shows  the  condyle  register  with  the  horseshoe  plate  attached,  to  which  the  lower  wax  bite-plate 
is  fastened:  .ST,  spring  lead  pencils;  P,  parallel  plates;  H,  horseshoe  plate;  F,  tinger  rests;  A,  place  for 
insertinff  holder. 


inserting  holder 


proximately  parallel  to  the  sides  of  one  of  the  slots  (Fig.  344).  Press 
the  point  of  the  axis  of  the  slotted  plate  through  the  card,  and  then 
mark  the  points  of  the  long  axis  of  the  plate  with  a  pencil.  This  will 
show  the  main  direction  of  the  path.  The  slotted  plate  is  taken  away, 
and  both  marked  points  are  joined  by  a  direct  line  (Fig.  344),  which  line 


Fig.  344 


Shows  how  the  main  direction  of  the  condyle  path  is  found  by  means  of  the  slotted  plate. 


is  continued  to  the  lower  boarder  of  the  card,  so  that  with  the  angle 
measure  one  can  determine  (see  Fig.  345)  the  acute  angle  which  this 
line  forms  with  the  lower  border  of  the  card.  As  this  lower  border  of 
the  card  is  held  (in  the  registering  of  the  path  of  the  condyles)  parallel 
with  the  parallel  plates,  which  in  turn  are  parallel  to  the  horseshoe 
plate,  and  this  latter  lies  in  the  plane  of  occlu.sion,  the  angle  measured 


THE  nysr  measuiuxg  instruments. 


373 


ill  this  way  must  corresjjoiul  exactly  with  the  shuit  of  the  path  of  the 
condyle  to  the  plane  of  occlusion. 

"The  slotted  plate  chosen  is  then  i)laced  in  position  on  the  articulator 
and  the  known  slant  fixed  by  means  of  the  engraved  degree  scale  on  the 
joint  of  the  instrument  (see  Fig.  331).  Then  proceed  in  the  same 
manner  with  the  registered  condyle  path  of  the  other  side. 


Fig.  34.5 


Shows  the  mode  of  measuring  the  angle  formed  bj*  the  condyle  path  and  the  lower  border  of  the  record- 
ing card. 

"Fig.  346  shows  a  recording  card  with  the  registered  condyle  paths 
of  the  right  and  left  sides,  which  have  been  measured  in  the  manner 
stated.  On  the  right  side  the  condyle  moves  in  a  slant,  the  angle  of 
which  is  44°  to  the  plane  of  occlusion  (Fig.  341,  P);  on  the  left  the 
measured  angle  registers  34°. 

"In  cases  where  the  curve  is  more  or  less  horizontal,  and  the  length- 
ened line  does  not  reach  the  lower  border  of  the  card,  a  line  is  drawn  from 


Fig.  346 


Shows  the  completed  measurements  of  the  condyle  path. 


the  side  of  the  card  tangent  to  the  lengthened  line  and  parallel  to  the 
lower  border  of  the  card  (Fig.  347). 

"The  objection  may  be  raised  to  my  method  of  measuring  that  the 
plane  of  occlusion  represented  by  the  wax  bite-plate  is  not  a  fixed  point, 
because  in  setting  up  the  artificial  teeth  one  is  obliged  to  change  this 
temporary  plane  of  occlusion  according  to  circumstances. 


374 


DATA    TO  BE   USED   IN  CONSTRUCTING  DENTURES. 


"This  objection,  however,  is  only  apparently  justified,  because  in 
reahty  not  only  the  angle  of  the  condyle  path  to  the  tenii)()rary  plane  of 
occlusion  is  obtained,  but  also  at  the  same  time  that  to  the  alveolar 
ridge,  or  to  the  mandilile  itself  as  a  whole. 

"If  the  temporary  ])lane  of  occlusion  is  changed,  the  degree  of  the 
angle  of  the  condyle  path  is,  of  course,  also  changed  to  agree  with  the 

Fig.  347 


new  plane  of  occlusion,  but  the  relative  relations  of  the  position  of  the 
mandible  itself  to  the  condyle  path  remain  just  the  same. 

"I  will  now  give  an  analysis  in  detail  of  the  condyle  path  curve  as 
illustrated  in  Figs.  344  and  346. 

"Fig.  348  shows  an  enlarged  diagram  of  a  left   and   right   condyle 


Fig.  348 

c 


R 


Analysis  of  a  right  and  left  condyle  path  as  secured  by  method  shown  in  Fig.  311:  C,  condyle  path; 
L,  left;  R,  right;  Oc,  plane  of  occlusion;  35-degree  angle  of  middle  part  of  path  to  plane  of  occlusion; 
r,  resting  position  of  condyle;  /?',  path  of  condyle  in  a  right  lateral  movement;  Z/>,  the  same  in  a  left 
lateral  movement;  o,  forward  bite  or  wide  opening  and  closing  movement. 


path  curve,  each  of  which  is  divided  into  its  chief  parts,  as  indicated 
by  the  different  lines. 

"From  the  description  of  this  diagram  it  can  be  seen  that  during 
the  forward  and  downward  movements  of  the  one  condyle,  the  other 
runs  more  or  less  backward  horizontally. 

"The  extreme  forward  movement  and  the  opening  and  closing  move- 
ments may  be  divided  into  two  parts:  First,  the  path  which  the  con- 


TIIK  arSI  MKISURINO  JNSTJiUMh'NTS. 


375 


(lyle  takes  in  a  sli<j;ht  lateral  movement,  and  second,  tlie  path  wliieli 
the  condyle  takes  in  its  movements  on  the  eminentia  articnlaris,  wiiicli 
is  more  or  less  horizontal,  and,  finally,  may  even  lead  upward. 

"As  the  Jast  part  of  the  path  as  represented  hy  dashes  in  Fig.  ,348  can 
only  occur  in  extreme  lateral  or  wide  oi)ening  movements,  and  is  of  no 
importance  in  mastication,  I  determine  only  the  degree  of  the  angle  of 
the  more  important  middle  part  of  the  curve  to  the  plane  of  occlusion. 
(In  the  case  represented  in  Fig.  348  the  angle  registers  35  degrees.) 

"It  does  not  often  happen  that  both  condyle  path  curves  have  the 
same  form  and  slant.  Some  examples  of  the  differences  in  form  and 
slant  between  left  and  right  condyle  path  curves  in  the  same  individ- 
ual may  be  seen  in  Fig.  351,  a  to  i.  The  specimens  in  the  same  figure 
from  m  to  q  show  that  other  differences  may  occur,  either  in  only  one 
or  in  both  joints  at  the  same  time,  between  the  path  of  the  opening 
movement  and  the  path  of  the  lateral  movement  (n  to  q).     For  prac- 


Diagram  of  a  number  of  condyle  path  angles.     (See  table.) 


tical  purposes  only  the  path  taken  in  the  lateral  movement  possesses 
any  value  in  the  setting  up  of  the  artificial  teeth  for  efi:'ective  mastica- 
tion, and,  therefore,  only  this  angle  is  measured. 

"In  Fig.  349  I  have  compiled  a  number  of  condyle  path  angles,  and 
from  these  statistics  it  can  be  seen  that  the  average  angle  is  about 
33  degrees. 

"The  accompanying  table  shows  the  same  cases  individually  ar- 
ranged, and  it  may  be  seen  from  it  that  in  about  half  the  cases  there  is 
a  difference  of  only  about  4  degrees  between  the  right  and  left  side. 
As  this  slight  difference  might  be  attributed  to  a  possible  mistake  in 
measuring,  it  can  be  truly  said  that  half  the  cases  which  I  have  measured 
had  the  same  condyle  path  angle  on  both  sides,  and  the  other  half  showed 
a  difference  of  between  5  and  22  degrees,  averaging  about  10  degrees. 
One  astonishing  case  of  exception  showed  51  degrees  on  the  right  side 
and  10  degrees  on  the  left  side,  a  difterence  of  41  degrees. 


376 


DATA    TO   BE    USED  IN  CONSTRUCTiyu    DENT  CUES. 


EXAMPLES   OF  ANGLES   OF   llIE   CONDYLE    PATH. 
(Same  cases  individually  arranged.) 


Right. 

Left. 

Difference 

Right. 
33° 

Left. 

38° 

Difference. 

54° 

54° 

0° 

5° 

40° 

40° 

0° 

43° 

38° 

5° 

33° 

33° 

0° 

35° 

30° 

5° 

51° 

50° 

1° 

30° 

25° 

5° 

26° 

27° 

1° 

26° 

20° 

6° 

39° 

.      3-0 

2° 

28° 

20° 

8° 

28° 

30° 

2° 

21° 

13° 

8° 

23° 

21° 

2° 

40° 

32° 

8° 

35° 

37° 

2°           i 

10° 

19° 

9° 

40° 

42° 

2° 

34° 

25° 

9° 

32° 

35° 

3° 

22° 

31° 

9° 

31° 

34° 

30 

30° 

40° 

10° 

33° 

36° 

3° 

28° 

39° 

11° 

37° 

40° 

3° 

40° 

25° 

15° 

5° 

9° 

4° 

29° 

45° 

16° 

36° 

40° 

4° 

46° 

29° 

17° 

10° 

14° 

4° 

23° 

45° 

22° 

"Fig.  850  shows  a  collection  of   condyle   path    forms,  from  which  I 
have  chosen  the  four  average  types  that  are  used  in  my  articulator  in  the 


Fig.  .3.50 


The  fdiir  average  forms  of  fonci\  le  path.'i.      Examples  of  foiulyle  path  forms  as  registercfl  in  edentulous 

patients. 


THE  UYSI  MEASURING  INSTRUMENTS . 


37: 


form  of  the  slotted  plates  represented  in  Fig.  :j44.  If  necessary,  other 
forms  may  be  made  from  thin  brass  plate.  These  slotted  plates  are  the 
condyle  path  gnides  of  the  articulator. 

"The  Small  Register.  Instrument  for  Determining  the  Path  of  Motion 
of  the  Anterior  Triangle  Point  in  a  Horizontal  Plane. — The  movement  of 
this  pt)int  in  a  vertical  plane  in  the  opening  and  closing  movement  has, 
as  has  alreadv  been  stated  in  the  opening  chapter,  been  measured  by 


Fig.  351 


a 


37" 


A 


■'3^ 


Mi 


40» 


a 


■'.iP'! 


:3f 


X 


51' 


e- 


25^ 


-\ 


.■•40" 


-40" 


/40f- 


■431 


/3^ 


..--30°: ^ 


■31° 


y^ 


'22 


Si' 


13' 


^      "V 


-■•5/' 


7/1 


z:^ 


iA^- 


■33' 


■33' 


n 


P 


■■  zo 


y 


45* 


.29' 


9 


+       is'. 


Tomes  and  Dolamore,  but  for  practical  purposes  that  has  no  value. 
Only  the  path  in  a  horizontal  plane,  which  varies  from  case  to  case,  need 
be  determined  for  our  purposes,  as  this  alone  has  an  influence  on  the 
setting  up  of  artificial  teeth. 

"To  secure  this,  I  proceed  as  follows:  The  shaded  part  of  the  horse- 
shoe plate,  as  shown  in  Fig,  353,  is  covered  with  a  thin  film  of  dark- 


378 


DATA   TO  BE   USED  IN  CONSTRUCTING  DENTURES. 


colored  wax,  wliicli  with  u  liot  instrumont  is  spread  to  the  tliiiuiess  of 
pa})er. 

"A  i)oiiited  marker  (the  small  register)  mounted  on  a  spring  is  now 
pressed  directly  over  the  median  line  of  the  upper  wax  model  after  hav- 
ing been  warmed  slightly,  and  with  a  hot  instrument  is  firmly  attached 
at  the  edges.  The  point  must  stand  out  about  1  mm.  over  the  occlud- 
ing surface  of  the  wax  model  (Fig.  352). 

"The  upper  and  lower  wax  models  are  again  placed  in  the  mouth  and 
held  in  position  by  a  little  tragacanth  powder,  and  the  patient  is  re- 
quested to  move  the  mandible  from  side  to  side.  The  jjoint  of  the  marker 
registers  these  movements  on  the  coating  of  wax  on  the  horseshoe  plate. 
At  first  these  recorded  movements  are  somewhat  irregular  and  inter- 
twine at  the  posterior  portion  of  the  wax-covered  part  of  the  plate 
(Fig.  353),  because  in  the  beginning  the  patient  pushes  the  mandible  too 
far  forward.  Without  an  efl'ort  to  correct  this  improper  position  of 
the  mandible,  this  movement  is  allowed  to  continue,  and  it  will  be  seen 
that  the  mandible,  owing  to  fatigue,  will  gradually  go  back  to  its  normal 


Fig.  352 


Fig.  3o3 


The  small  register  fastened  t"  the  uppi 


wax  iiKidel.       Horseshoe  plate  with  registered  incisor  path 


distal  position,  and  its  path  will  be  recorded  by  a  correct  regular  curve 
(K  M  K). 

"The  outer  line  of  these  tangled  markings  is  the  normal  path,  the 
middle  is  the  true  median  line,  and  also  the  normal  closing  point  in  the 
resting  (occlusal)  position  of  the  mandible. 

"When  the  point  of  the  marker  is  at  M  (Fig.  353)  or  in  resting  posi- 
tion (Fig.  354),  the  usual  marks  are  made  on  both  wax  models  at  the 
notches  prepared  in  the  horseshoe  plate  (Fig.  353,  S  S)  to  show  the 
proper  positions  of  the  models  when  being  fastened  with  plaster  to  the 
articulator. 

"This  instrument  is  of  great  service  in  the  use  of  any  articulator, 
because,  leaving  aside  its  special  purpose,  which  will  be  explained  later, 
it  is  an  excellent  help  in  securing  the  normal  resting  position  of  the 
mandible. 

"From  the  angle  K  ]\I  K  the  relative  position  of  the  balancing  or 
rotation  points  of  the  mandible  can  be  determined  (Fig.  355). 

"If  both  sides  of  this  angle  are  extended  beyond  the  intersecting 


THE  GYSI  MEASURING  INSTRUMENTS. 


379 


Fui.  354 


Registering  the  incisor  path.     (Wilson,  after  Gysi.) 


Fig.  355 


\3cfn     IOc/77       7c/77 


\ 


1cm  lOc/77      13c/77 


380  DATA    TO   HK   USED   IX  COSSTRUCTiya   DKNTURKS. 

point  (see  dotted  linos  in  Fi^'.  'Ai)2),  the  direction  of  tlic  path  of  the  h)\\cr 
incisors  and  canines  (hirinji;  mastication  is  shown. 

"This  angle  of  the  incisor  path  varies  in  difiVrent  inihxidnals,  and 
therefore  the  center  of  rotation  varies  c()rresj)ondinji;l\ .  In  my  investi- 
<,'ations  1  have  found  that  the  relative  distances  between  these  rotation 
points  may  vary  from  7  to  K!  cm.  measured  In  a  line  drawn  throufrli 
the  centre  of  the  condyles. 

"In  some  cases  these  rotation  i)()ints  may  lie  still  farther  away  from 
the  condyles.  As  the  a\erafi:e  distance  (according  to  Bonwill)  hetween 
the  condyle  centres  is  10  cm.,  the  rotation  point  may  lie  sometimes  inside 
and  sometimes  outside  of  the  condyles.  Xevy  often  the  rotation  point 
in  the  same  individual  may  be  differently  situated  on  each  side,  e.  g., 
the  one  may  lie  inside,  and  the  other  outside  the  condyle. 

"The  importance  of  determining  the  exact  position  of  these  rotation 
points  can  be  best  understood  by  making  a  drawing  hke  that  in  Fig.  355 
on  a  triangular  piece  of  cardboard,  and  recording  the  movements  of 
the  incisor  point  of  the  triangle  l)y  sticking  a  pin  successively  through 
the  balancing  j)()ints  of  7,  10,  and  13  cm.,  and  with  a  sharp  lead  pencil 
point  inserted  through  the  incisor  point  recording  the  lateral  movements. 
The  result  will  show  three  difi'erent  paths. 

"Figure  356  shows  how  both  condyles  carry  out  the  same  movement 
(in  lateral  movements)  when  the  rotation  points  lie  outside  of  the  con- 
dyles 12  cm.  apart,  while  the  lead  pencil  points  attached  to  the  large 
register  will  mark  paths  in  the  opposite  direction. 

"Figure  357  shows  how  both  the  condyles  and  the  lead  pencil 
points  of  the  large  register  will  record  opjiosite  paths  in  the  lateral 
movements  when  the  rotation  ]K)ints  lie  inside  the  condyles. 

"It  is  clear  from  these  two  illustrations  that  it  is  possible  to  deter- 
mine the  position  of  the  rotation  points  from  the  relations  of  the  paths 
(of  the  forward  movements  on  the  right  sides  and  the  backward  move- 
ments on  the  left  sides  of  Figs.  356  and  357)  recorded  by  the  registering 
instrument;  but  this  method  would  not  be  accurate  enough,  owing  to 
the  short  length  of  the  paths,  and,  therefore,  from  even  small  mistakes  in 
measuring  great  differences  would  arise. 

"From  the  position  of  these  rotation  points  it  is  plain  that  they  could 
not  be  considered  as  anatomically  fixed  points,  but  rather  as  ideal 
balancing  points,  and  for  that  reason  their  existence  has  remained  un- 
recognized so  long.     Walker  recognized  their  existence  in  1896.^ 

"A  balancing  point  is,  therefore,  the  axis  of  rotation  resulting  from  the 
diverse  contractions  of  the  masticatory  muscles,  and  happens  to  coin- 
cide only  now  and  then  with  the  condyles.  As  it  is  impossible  to  imitate 
the  muscles  of  mastication  on  an  articulator,  these  balancing  points 
must  be  substituted  by  mechanical  centres  of  rotation,  the  positions 
of  which  can  be  changed  from  case  to  case. 

"The  natural  condyles  camiot  be  considered  as  true  rotation  points 
or  axes  around  which  the  various  movements  of  the  mandible  occur,  but 

'  .S.-0  Dental  Cosmos,  January,  1896,  p.  34,  and  Jul.w  ISOC,  p.  r,7^. 


THE  GYSI  MEASUlilNa   LXSTRUMENTS. 


,381 


should  ()iil\   1)0  rognrdod  as  fixed  <;ui(les  of  the  mandible  in  its  niovc- 
mcMits. 


Fio.  356 


Fig.  357 


Figs.  356,  367.-Rst,  Registering  point;  RF,  registering  surface;  W,  soft  parts  TV.tlSedn^ 
balancing  point;  G,  condyle;  A,  B,  moving  path  of  the  chief  points  of  the  mandible  and  of  the  reg.stermg 
points  in  lateral  movements. 

"It  is,  therefore,  not  necessary  to  try  to  imitate  the  natural  condyles 
nor  the  glenoid  fossa  on  an  articulator,  but  it  is  necessary  to  imitate  the 


382  DATA    TO  BE   USED  IN  CONSTRUCTING   DENTURES. 

muscle  movements  by  constricting;  mechanical  centres  of  rotation  (as 
already  stated)  and  mechanical  condyle  path  guides,  as  represented  in 
m^•  articulator  by  slotted  plates. 


Fig.  358 


Fig.  359 


IOc/77      7cm 


1cm      lOc/n 


THE  GYSl  MEASURING  INSTRUMENTS.  383 

"The  importance  of  knowing  the  relative  position  of  the  balancing 
points  is  made  clear  in  Figs.  358  and  359. 

"These  balancing  points  can  be  constrncted  either  geometrically 
with  compass  and  rule,  or  simply  by  drawing  on  a  piece  of  cardboard 
an  equilateral  triangle  with  sides  of  about  13  cm.  in  length,  on  which 
the  outline  of  the  mandible  is  drawn,  with  the  teeth  as  in  Figs.  358  and 
359.  Attach  with  wax  small  graphite  points  between  the  central  inci- 
sors, also  over  the  canines,  and  over  the  middle  of  each  molar.  Grind 
these  points  to  an  equal  height  with  a  piece  of  sand-paper.  Set  the 
cardboard  with  the  points  downward  on  a  piece  of  writing  paper,  insert 
a  pin  through  the  middle  of  each  condyle,  and  make  lateral  masticating 
motions  with  the  cardboard,  when  the  graphite  points  will  record  their 
individual  movements.  If  the  same  experiment  is  made  with  the  pin 
inserted  through  the  extreme  balancing  points  of  7  and  13  cm.  distance, 
quite  different  results  will  be  obtained.  These  two-dimensional  tracings 
as  shown  in  Figs.  358  and  359  are  not  quite  accurate;  the  angles  would  be 
slightly  different  in  a  normal  natural  case,  where  there  is  an  overbite  of 
incisors,  and,  therefore,  a  three-dimensional  movement. 

"In  cases  where  the  balancing  points  lie  outside  of  the  condyles,  the 
mandible  in  lateral  movements  moves  at  the  same  time  strongly  for- 
ward. As  the  lower  incisors  are,  however,  somewhat  hindered  by  the 
overbite  of  the  upper  incisors,  the  mandible  glides  downward  and  out- 
ward on  the  lingual  surfaces  of  the  upper  incisors ;  consequently  a  longer 
overbite  of  the  canines  and  higher  cusps  of  the  molars  are  necessary  in 
order  that  the  teeth  may  not  move  too  quickly  away  from  each  other. 

"When,  however,  the  positions  of  the  balancing  points  lie  inside  of 
the  condyles,  the  lower  incisors  move  forward  less  obliquely  and  almost 
directly  sideward,  thereby  for  some  distance  the  contact  with  the 
upper  incisors  is  secured ;  consequently  the  overbite  may  be  less  and  the 
cusps  of  the  molars  may  be  lower. 

"The  positions  of  the  balancing  points  are  still  more  important  in 
regard  to  the  relative  positions  of  the  upper  and  lower  canines.  To 
present  this  fact  more  clearly,  the  path  of  the  canine  in  Fig.  358  is  pre- 
sented on  the  left  side  of  Fig.  359,  showing  the  difference  in  the  paths 
of  the  lower  canines  according  to  whether  the  balancing  point  of  7  cm. 
or  of  13  cm.  asserts  itself. 

"Fig.  360,  for  example,  shows  a  side  view  of  the  canines  in  the  normal 
occlusion  as  they  are  usually  set  up  in  an  articulator  for  a  practical  case. 
Fig.  361  shows  the  same  in  a  lateral  movement.  If,  however,  the  patient 
has  a  difference  balancing  point,  the  canines  will  describe  another  path, 
and  the  upper  canine  vnl\  not  pass  properly  through  the  space  between 
the  lower  bicuspid  and  canine,  but  ^^ill  rather  strike  against  the  cusp 
of  the  latter,  thus  forming  the  only  contact  point  of  the  tooth  rows, 
and  thereby  tilting  and  loosening  the  upper  plate  (Fig.  362).  With 
such  an  artificial  denture  lateral  movements  are  absolutely  impossible, 
and  the  patient  in  eating  is  compelled  to  carry  on  only  up  and  down 
movements,  or  else  ultimately  the  cusps  of  the  canines  as  well  as  those 


384 


DATA    TO  BE    USED  IN  CONSTRUCTING   DENTURES. 


of  the  bicuspids  must  be  ground  oil",  whereby  the  natural  appearance  and 
usefuhiess  of  the  denture  is  destroyed. 

"As  1  have  already  stated,  the  mandible  cannot  make  a  free  lateral 
movement,  being  partly  prevented  by  the  overbite  of  the  upper  incisors. 
Therefore  the  lateral  movements  are  combined  with  the  opening  and 
closing  movements.     If  no  overbite  were  present,  the  front  teeth  in  the 


Fig.  360 


Fig.  361 


Normal  occlusion  of  artificial  teeth. 


Normal  position  in  a  lateral  movement 
when  the  correct  balancing  point  has  been 
secured. 


lateral  bite  would,  after  a  short  grinding  movement,  glide  away  from  each 
other,  and  the  whole  force  of  the  masticatory  muscles  would  rest  on  the 
molars  exclusively,  so  that  the  latter  would  be  worn  away  altogether  too 
quickly.  These  conditions  may  be  noted  in  the  ruminants  (horses, 
cows,  etc.);  the  increased  wearing  away  of  the  molars  is,  however, 
compensated  by  their  numerous  and  deep  enamel  folds. 

"The  upper  incisors,  because  of  their  slanting  surfaces  on  the  lingual 
side,  have  the  important  function  of  acting  as  the  anterior  guiding  and 

Fig.  362 


Incorrect  position  in  a  lateral  movement  when  the  balancing  point  of  the  articulator  differs  from  the 

natural  one. 


gliding  plane  of  the  mandible,  while  the  condyles  and  the  eminentia 
articularis  act  as  guides  of  the  posterior  movements  of  the  mandible. 
These  latter  guiding  planes  of  the  two  posterior  points  of  the  triangle 
have  a  slant  of  from  5  to  50  degrees,  while  the  anterior  point  of  the 
triangle  or  inci.sor  guide  exhibits  a  slant  of  from  50  to  70  degrees  to  the 
occlusal  plane. 

"In  edentulous  patients  it  has  been  impo.ssible  so  far  to  determine  the 
previous  guide  angle  of  the  incisor,     I  believe,  however,  that  this  rep- 


THE  GYSI  MEASURING  INSTRUMENTS.  385 

resents  a  racial  phenomenon,  directly  dependent  upon  the  facial  angle. 
From  a  small  number  of  measurements  I  have  found  that  the  angle  of 
the  slant  of  the  lingual  surfaces  of  the  incisors,  which  form  the  incisor 
guide,  amounts  to  15  degrees  less  than  the  facial  angle  formed  hy  a  line 
connecting  the  outer  ear  with  the  base  of  the  nose,  and  a  line  connecting 
the  most  prominent  part  of  the  forehead  with  the  base  of  the  nose. 
These  measurements  are,  however,  too  small  in  number  and  too  super- 
ficial to  serve  as  full  proofs. 

"If  the  angle  of  the  guiding  surfaces  of  the  incisors  is  determined 
in  such  an  arbitrary  way,  it  is  of  no  practical  value  in  an  artificial  den- 
ture. For  practical  reasons,  which  will  be  discussed  in  a  subsequent 
chapter,  I  nearly  always  choose  the  lowest  angle,  of  about  45  degrees 
or  less,  for  this  gliding  angle  of  the  incisors. 

"From  all  these  considerations  it  follows  unquestionably  that  in 
lateral  movements  the  centres  of  rotation  or  balancing  points  lie  approx- 
imately on  a  line  passing  through  the  centre  of  the  condyle  region,  and 
that  these  balancing  points  in  different  individuals  may  lie  either  on  the 
inside  or  the  outside  of  the  condyles. 

"As  I  shall  show  later,  the  mandible  in  opening  and  closing  rotates 
around  another  centre,  which,  however,  has  no  influence  in  the  setting  up 
of  the  teeth  for  articulation,  and,  therefore,  need  not  be  considered  in  the 
construction  of  an  articulator.  In  the  Walker  articulator  this  opening 
axis  can  be  attached,  and  is  used  when  the  plane  of  articulation  is  to  be 
lowered  or  raised.  In  the  Kerr  articulator  the  true  axis  of  rotation  on 
opening  is  permanently  fixed  on  the  articulator.  In  my  articulator 
the  ordinary  axis  for  opening  and  closing  movements  is  used — as  it  has 
no  influence  on  the  slant  of  the  condyle  path — in  the  same  way  as  in 
Walker's  and  Christensen's  articulator. 

"From  these  observations  it  follows  that  in  the  construction  of  an 
articulator  the  following  points  should  be  considered: 

"1.  An  individually  changeable  slant  of  the  condyle  path. 

"2.  An  individually  changeable  form  of  the  condyle  path. 

"3.  A  changeable  incisor  guide. 

"4.  Two  individually  changeable  balancing  of  rotation  points. 

"5.  The  incisor  guide  must  not  change  the  slant  of  the  condyle  path; 
the  slant  of  the  condyle  path  must,  therefore,  be  independent  of  the 
opening  movement." 


25 


CHAPTER    XL 

THE   PRINCIPLES   UNDERLYING   THE   RETENTION   OF   PLATE 

DENTURES. 

By  Charles  R.  Turner,  D.D.S.,  M.D. 

After  all  the  necessary  data  have  been  obtained  from  the  patient, 
we  are  ready  to  proceed  to  the  design  and  construction  of  the  artificial 
denture.  Before  undertaking  the  design  of  a  denture  which  shall  fulfil 
the  aesthetic  requirement  in  the  restoration  of  the  facial  appearance 
and  the  functional  reciuirements  of  mastication,  speech,  etc.,  it  will  be 
necessary  to  see  that  a  fundamental  and  important  mechanical  de- 
mand upon  it  is  satisfied.  It  is  essential,  first,  that  the  denture  shall 
be  adequately  supported  upon  a  base  to  resist  the  force  exerted  upon  it 
in  use,  and  second,  that  it  shall  be  firmly  and  stably  maintained  upon 
this  base  during  its  use. 

Artificial  dentures  receive  their  support  from  two  sources — thenatural 
teeth  or  roots,  and  the  mucous  membrane  covering  the  maxilla  and 
mandible.  According  as  this  support  is  derived,  we  have  dentures 
divided  into  the  following  classes: 

1.  Crownri  supported  upon  natural  roots. 

r  A.     Fixed — supported  upon  natural  roots. 

2.  Bridge  dentures    I  fa.     Supported  upon  natural  roots. 

[  B.     Removable — ■  I  h.    Supported  both  by  natural  roots  and 

i  mucous  membrane.     (Saddle  bridges.) 
\  A.    Maintained  and  supported  by  roots  and  mucous  membrane. 

3.  Plate  dentures      s  B.    Maintained  by  teeth — Supported  by  membrane.      (Clasp 

(  dentures.) 

4.  Pla re  dentures  receiving  their  support  solely  through  mucous  membrane,   and 
maintained  independent  of  natural  teeth. 

The  first  two  of  these  classes  are  so  important  that  they  will  be  con- 
sidered separately  in  succeeding  chapters  (XVI.  and  XVII.),  and  this 
chapter  will  treat  only  of  the  last  two,  or  plate  dentures. 

The  mucous  membrane  covering  the  maxilla  and  mandible  is  nor- 
mally firm,  resistant,  and  comparatively  insensitive.  It  affords  to  a 
carefully  adapted  base-plate  upon  which  are  mounted  artificial  teeth, 
sufficient  support  to  withstand  the  force  exerted  in  mastication,  pro- 
vided the  base-plate  area  is  adequately  proportioned  to  the  number  of 
teeth  it  carries,  and  hence  to  the  stress  which  devolves  upon  it  in  use. 
Under  these  conditions  the  support  is  afforded  by  the  membrane 
without  protest,  the  bony  substructure  being  of  sufficient  strength 
to  bear  the  stress  transmitted  to  it.  Plate  dentures  depend  wholly 
upon  the  mucous  membrane  for  their  support,  with  the  exception, 
however,  of  the  small  number  of  plates  which  receive  additional  sup- 
386 


THE  METHOD   OF   USE  OF  PLATE  DENTURES.  387 

port  from  teeth  or  roots  wliose  chief  function  is  the  maintenance  of  the 
apphance.  These  exceptions  are  so-called  removable  saddle  bridges, 
dentures  combining  the  principles  of  plate  and  bridge-work,  and  some 
])artial  plate  dentures. 

RATIONALE    OF    THE   METHOD    OF   USE    OF   PLATE   DENTURES 

The  satisfactory  utilization  of  a  plate  denture  for  purposes  of  mas- 
tication depends  also  upon  its  firm  maintenance  in  position  upon  its  sup- 
porting base.  This  usually  involves  one  or  both  of  two  things.  The 
first  is  a  purely  mechanical  consideration — the  maintenance  of  the 
plate  in  situ  by  some  physical  means.  The  second  is  dependent  upon 
the  cultivation  of  such  co-ordinations  of  the  muscular  structures  of  the 
mouth  as  will  assist  in  maintaining  the  plate  in  place.  It  will  be 
seen  later  that  cases  diifer  vastly  in  the  physical  possibilities  which  they 
offer  for  the  stable  retention  of  the  plate,  as  do  patients  in  their  ability 
to  cultivate  the  fine  co-ordinations  necessary  for  the  successful  use  of 
the  denture.  Just  as  the  former  are  less  in  amount  in  a  given  case,  is 
there  greater  demand  upon  the  wearer  of  the  denture  in  the  latter  way. 
Even  under  the  physical  conditions  most  favorable  for  retention,  some 
assistance  from  the  muscular  structures  will  always  be  required  of  the 
patient.  It  is  almost  ^lever  the  case  that  a  plate  is  inserted  and  the 
patient  can  at  once  proceed  to  eat  with  facility.  The  movements  which 
resulted  in  mastication  with  the  natural  denture  do  not  succeed  at  first 
with  the  artificial.  At  best  the  appliance  is  but  a  substitute,  and  it 
devolves  upon  the  patient  to  learn  to  use  it.  The  probable  success  in  the 
use  of  the  denture  may  be  judged  in  some  measure  by  the  accomplish- 
ments of  the  patient  in  other  fine  co-ordinations,  such  as  sewing,  or  other 
delicate  manipulations.  It  is  unfortunate  that  at  the  period  of  life  at 
which  artificial  dentures  are  usually  required,  the  ability  to  acquire 
new  co-ordinations  is  greatly  reduced. 

Frequently  special  effort  is  made  to  take  advantage  of  this  power 
of  the  muscular  structures  of  the  lips,  cheeks,  and  tongue  to  grasp  the 
dentures  and  hold  them  in  place.  It  has  been  stated  that  these  struc- 
tures in  the  mouths  of  some  patients  are  susceptible  of  great  education. 
To  utilize  this  power  to  the  utmost  it  is  advisable  to  form  upon  the  buccal 
and  labial  margins  of  all  upper  dentures  a  projecting  rim  which  can  be 
grasped  by  the  lip  and  cheek  muscles.  This  becomes  embedded  in  the 
tissues  and  affords  to  them  a  better  means  of  grasping  the  sides  of  the 
plate.  In  some  cases  in  which  the  natural  conditions  of  the  upper  jaw 
are  unfavorable  to  firm  plate  retention,  it  is  possible  to  extend  this 
principle  to  the  point  of  making  decided  projections  on  the  buccal 
surface  of  the  plate.  The  author  has  obtained  a  very  satisfactory 
result  from  the  use  of  this  measure  in  a  case  of  syphilitic  necrosis,  in 
which  one  of  the  antra  was  perforated,  the  entire  alveolar  process  hav- 
ing been  lost  and  the  roof  of  the  mouth  being  almost  a  plane  surface. 
The  use  of  springs  in  this  case  seemed  inadvisable  because  all  of  the 
lower  teeth  remained  intact.     A  vulcanite  plate  was  made  with  a  pro- 


388  THE  UKTKyTlUN  OF  PLATE  DEXTURES. 

jection  in  the  buccal  region  which  avoided  tiie  anterior  niarf^in  of  the 
masseter  muscle  and  which  fitted  into  a  depression  in  the  cheek  located 
above  the  ])osition  of  the  risorius  muscle.  The  patient's  cheek  was 
somewhat  distended  by  the  appliance,  but  in  the  course  of  time  a  marked 
depression  was  made  in  the  muscular  structures  of  the  cheek,  and  the 
patient  learned  to  maintain  the  denture  satisfactorily  in  place. 

Patients  must  learn  to  manijnilate  the  food  between  the  teeth,  and  to 
aj)ply  the  force  used  in  crushing  it  by  such  movements  of  the  mandible 
as  will  tend  to  keep  the  dentures  in  place.  This  is  often  done  by  chew- 
ing on  both  sides  simultaneously,  and  by  using  only  the  up  and  down 
motions  of  the  mandible.  A  large  number  of  full  upper  and  lower 
dentures  now  in  ser\ice  admit  of  no  other  method  of  use,  because  of 
the  form  and  positions  of  the  teeth.  It  will  be  seen  in  the  succeeding 
chapter  that  the  teeth  should  be  shaped  and  placed  with  a  view  of  mak- 
ing possible  the  lateral  movements  of  the  mandible,  which  give  more 
effective  masticative  results,  and  patients  may  thus  acquire  masticatory 
habits  of  greater  utility. 

Patients  acquire  the  ability  to  maintain  an  upper  plate  in  place  by 
grasping  it  ^^^th  their  cheek  muscles  and  by  manipulating  the  tongue 
to  support  it. 

In  lower  cases  where  retention  of  the  plate  promises  to  be  difficult, 
and  particularly  where  no  form  of  partial  denture  has  previously  been 
worn,  it  is  sometimes  advisable  to  permit  a  tooth  or  teeth  to  remain, 
even  when  it  is  evident  they  will  last  but  a  short  time.  These  are  of  great 
service  in  staying  the  plate  and  in  keeping  it  in  place  upon  the  alveolar 
ridge,  and  serve  to  tide  patients  over  that  first  period  during  which 
they  are  getting  accustomed  to  the  use  of  the  appliance.  Such  teeth, 
of  course,  should  be  carefully  preserved  w^hen  they  may  be  clasped  and 
made  of  more  permanent  service,  but  reference  here  is  made  to  those 
teeth  only  whose  retention  can  be  expected  for  a  short  time  at  best. 
It  is  impossible  to  estimate  the  value  of  this  procedure  to  some  patients, 
who,  after  having  become  accustomed  to  the  use  of  the  plate  with  the 
assistance  of  the  natural  teeth  to  maintain  it,  readily  acquire  the  use 
of  a  full  plate  when  the  natural  teeth  are  lost. 

In  the  case  of  lower  dentures  it  is  always  advisable  to  so  form  them 
that  they  do  not  encroach  upon  the  space  ordinarilx-  occupied  by 
the  tongue.  In  a  case  in  which,  by  reason  of  resorption  of  the  upper 
alveolar  process  it  is  necessary  to  have  a  lower  {)late  narrow  from  side 
to  side  in  order  that  the  teeth  may  articulate,  it  is  achisable  to  make 
its  lingual  surface  slightly  concave:  the  tongue  will  not  only  fit  into 
this  space,  but  may,  in  a  measure,  assist  in  maintaining  the  plate  in 
place  by  grasping  the  lower  edge  of  the  lingual  surface.  The  extension 
of  the  distal  portion  of  a  lower  plate  lingually  to  produce  a  projection 
which  may  be  grasped  by  the  tongue  has  been  recommended.'  ^^here 
this  extension  would  not  seriously  interfere  with  the  movement  of  the 
tongue,  and  where  in  addition  the  tongue  could  obviously  take  advan- 
tage of  the  extension  for  the  purpose  indicated,  it  may  be  an  advisable 
y)rocedure. 

'  The  Dental  Cosmos,  vol.  xxxviii,  p.  41. 


AIDS   TO   THE  RETENTION   OF   UPPER  PLATE  DENTURES.      389 

MECHANICAL  AIDS  TO  PLATE  RETENTION 

The  purely  mechanical  factors  which  contribute  to  the  retention  of 
a  plate  are  as  follows: 

1.  Correct  plate  outline. 

2.  Correctly  articulating  teeth. 

3.  Physical  means  of  retention. 

The  first  two  are  largely  negative  in  character  in  that  a  violation  of 
the  principles  of  their  correct  determination  may  become  a  factor  to 
depose  the  denture.  Pains  must  be  taken  that  they  do  not  serve  to 
displace  the  plate,  but  are  so  disposed  as  to  most  favor  its  stable  reten- 
tion.    The  plate  outline  will  be  discussed  under  a  subsequent  heading. 

In  the  chapter  on  articulation  of  the  teeth  (Chapter  XII.)  will  be 
found  a  description  of  the  best  manner  of  setting  the  teeth  to  prevent 
a  displacement  of  the  plate.  Suffice  it  here  to  say  that,  as  far  as  pos- 
sible, they  should  be  arranged  to  receive  the  force  of  mastication  in  such 
direction  as  will  not  displace  the  plate  through  leverage,  but,  on  the 
contrary,  will  maintain  it  in  situ.  This  object  is  in  part  accomplished 
by  having  the  distal  teeth  on  opposite  sides  of  the  plate  strike  at  the 
same  time,  in  order  to  balance  their  separate  tendencies  to  displace  it 
through  leverage.  The  physical  forces  of  adhesion  and  atmospheric 
pressure  are  utilized  to  maintain  upper  plate  dentures  in  place. 

Lower  dentures  are  held  in  place  by  gravity  and  to  some  extent  by 
adhesion  to  the  mucous  membrane  upon  which  they  rest.  Springs 
extending  from  an  upper  to  a  lower  denture  have  been  used  to  maintain 
the  plates  in  situ,  and  partial  dentures  often  utilize  the  remaining  natural 
teeth  to  sustain  them,  attachment  to  them  usually  being  by  means  of 
clasps.  These  several  factors  in  plate  retention  will  be  discussed  in 
detail. 


PHYSICAL  AIDS  TO  THE  RETENTION  OF  UPPER  PLATE  DENTURES 

Adhesion. — -This  may  be  defined  as  the  molecular  attraction  existing 
between  the  particles  of  two  bodies  whose  surfaces  are  in  contact.  It 
acts  between  two  solids  whose  surfaces  accurately  fit  together,  or  be- 
tween a  solid  and  a  liquid,  or  a  solid  and  a  gas.  The  force  of  adhesion 
is  directly  proportional  to  the  area  of  the  surfaces  in  contact,  and  it 
offers  the  greatest  resistance  to  a  force  tending  to  separate  these  surfaces 
by  acting  at  right  angles  to  them.  Contact  of  the  surfaces  is  essential  to 
the  maintenance  of  the  adhesion,  since  the  moment  they  are  separated, 
the  adhesion  is  broken  up.  Adhesion  is  of  value  more  or  less  in  the  re- 
tention of  all  plate  dentures,  full  or  partial,  upper  or  lower.  It  is  of 
particular  service  in  the  part  which  it  plays  in  the  retention  of 
upper  dentures. 

The  retention  of  upper  plates  by  this  means  presents  a  number  cf 
interesting  points  for  consideration.  The  problem  is  to  make  a  plate, 
covering  the  area  contained  within  the  plate  outlines,  which  shall  have 


390  THE  HETESTIOS  OF  PLATE  DENTURES. 

the  greatest  adhesion,  and  hence  offer  the  greatest  resistance  to  a  dis- 
phicing  force.  Other  things  being  ecjual,  the  plate  area  should  be  as 
large  as  possible,  since  the  adhesion  is  proportional  to  this  area.  The 
area  is  Umited  solely  by  the  necessity  for  not  encroaching  upon  tissues 
whose  movements  would  result  in  the  displacement  of  the  denture. 
The  outlines  and  contours  of  a  plate  should  not  be  carried  to  re- 
gions where  they  are  impinged  upon  by  tissues  moved  in  mastication, 
laughter,  or  speech,  since  the  plate  must  not  be  unseated  by  these 
movements.  While  it  cannot  always  be  entirely  free  from  the 
deposing  influence  of  moving  tissue,  as  in  cases  where  it  carries 
large  contours,  yet  the  effort  should  be  made  to  reduce  to  the  minimum 
all  these  displacing  influences,  and,  in  every  case,  the  active  forces  of 
retention  must  over})alance  and  counteract  them. 

For  a  full  upper  denture  the  boundaries  of  the  plates  should  be  as 
follows:    (Fig.  ,363.)     Beginning  at  the  median  line  of  the  mouth,  the 

Fig.  363 


Plate  outline  for  full  unper  denture. 


plate  outline  should  be  placed  low  enough  to  avoid  the  frienum  of  the 
upper  lip.  It  should  then  ascend  into  the  incisive  fossa  below  the  hne 
of  reflection  of  the  mucous  membrane  from  the  alveolar  process  to  the 
lip,  and  over  the  canine  eminence  at  a  somewhat  higher  level,  until  it 
reaches  the  interspace  anterior  to  the  first  bicuspid,  when  it  descends  to 
avoid  the  anterior  margin  of  the  buccinator  muscle.  It  will  be  remem- 
bered that  there  are  no  muscular  attachments  to  the  maxilla  in  the  in- 
cisive fossa  and  over  the  canine  eminence,  and,  as  this  underlies  a 
portion  of  the  face  which  will  require  considerable  support  from  the 
denture,  the  plate  outline  may  be  carried  proportionately  higher 
here  than  elsewhere.  From  the  anterior  border  of  the  buccinator  the 
boundary  must  be  low  enough  to  give  full  play  to  this  muscle,  and  the 
several  plicae  or  folds  of  the  mucous  membrane  extending  between  the 
process  and  cheek,  commonly  observed  in  this  region,  must  be  avoided. 
When  the  tuberosity  is  reached,  the  plate  outline  may  again  ascend  to 


AIDS  TO   THE  RETENTT02^   OF   UPPER  PLATE  DES TUBES.      .'391 

a  higher  level,  rounding  It  to  reach  the  palatal  vault.  It  must  he  re- 
membered that  the  anterior  margin  of  the  masseter  muscle  is  about 
opposite  the  second  molar  tooth,  so  the  plate  contours  in  this  region 
must  avoid  it. 

Beside  giving  a  plate  of  the  greatest  possible  area,  another  thing  is 
accomplished  by  having  the  plate  outline  follow  this  course  along  the 
labial  and  buccal  surfaces  of  the  alveolar  ridge.  This  provides  for 
the  exclusion  of  air  around  this  part  of  the  periphery  of  the  plate,  a 
condition  which  we  have  seen  is  necessary  for  adhesion.  The  lips 
and  cheeks  thus  form  curtains  to  cover  the  edge  of  the  plate,  and 
they  constantly  act  as  barriers  to  the  ingress  of  air.  So  long  as  the 
lips  and  cheeks  are  closely  applied  to  these  portions  of  a  denture,  the 
plate  maybe  pulled  upon  in  front  with  considerable  force  without  the 
admission  of  air  at  the  margins  and  the  consequent  breaking  up  of  its 
adhesion.  This  is  especially  true  if  the  alveolar  ridge  is  pro- 
nounced and  has  not  been  absorbed,  and  the  soft  tissues  are  attached 
to  it  externally  at  a  high  level.  It  is  generally  known  that  the  maxilla 
most  favorable  to  the  stable  retention  of  a  plate  denture,  other  things 
being  equal,  is  one  in  which  the  alveolar  process  is  well  defined  and 
which  has  a  broad  high  vault.  A  high  pointed  vault  affords  condi- 
tions less  favorable  for  the  secure  attachment  of  a  denture,  because 
the  plate  more  readily  slides  upon  the  slanting  sides  of  the  vault, 
the  ordinary  displacing  tendency  not  acting  at  a  right  angle  to  such 
surfaces;  while  aflat  mouth,  in  which  the  ridge  has  almost  entirely 
disappeared,  is,  of  course,  worst  of  all,  because  of  the  easy  access  of  air 
to  the  plate  edges.  In  proportion,  however,  as  the  tissues  are  at- 
tached at  a  high  level  on  the  buccal  and  labial  surfaces  and  there  has 
been  small  absorption  of  the  ridge,  is  it  possible  to  make  retention 
secure.  Closeness  of  the  contact  of  these  plate  margins  to  the  alve- 
olar ridge  may  be  accentuated  by  measures  to  be  discussed  later. 

The  posterior  margin  of  the  plate  should  be  far  enough  forward  to 
avoid  any  possible  displacement  caused  by  the  movements  of  the  soft 
palate.  This  line  corresponds  in  some  mouths  with  the  end  of  the 
hard  palate,  while  in  others  it  is  considerably  anterior  to  this.  The 
line  of  movement  may  be  observed  by  having  the  patient  open  the 
mouth  and  pronounce  the  syllable  "ah".  As  this  is  the  part  of  the 
periphery  of  the  plate  where  it  is  most  difficult  to  exclude  the  air,  it  is 
desirable  to  have  the  plate  extend  back  until  its  margin  is  laid  down 
on  soft  tissue  and  its  contact  therewith  accentuated.  It  is  also  de- 
sirable to  avoid  contact  of  the  plate  margin  with  the  distal  end  of  the 
hard  median  ridge,  although  this  is  not  always  possible.  In  cases  of 
extreme  difficulty  it  is,  therefore,  permissible  to  have  the  plate  outline 
slightly  encroach  upon  the  movable  area,  so  slightly,  however,  that 
the  advantage  obtained  in  the  matter  of  the  exclusion  of  air  is  not 
outweighed  by  the  displacing  influence  of  the  palatal  muscles.  This 
advantage  should  be  gained  always  where  the  softness  of  the  alve- 
olar process  anteriorly  permits  a  rocking  of  the  plate  and  hence  a 
displacement  under  stress  in  the  rear.      It  must  be  borne  in  mind, 


392 


THE  RETENTIOX  OF  PLATE  DENTURES. 


however,  that  this  encroaches  upon  an  irritable  area  in  many  throats 
and  if  the  pLate  extends  back  too  far,  some  patients  may  complain 
of  nausea  from  this  cause.  In  such  cases  a  little  patience  and  persever- 
ance on  their  part  will  accustom  them  to  the  presence  of  the  plate,  if  it 
be  vital  for  retention,  and,  if  it  is  not,  the  plate  may  be  trimmed. 

The  adhesion  of  all  full  upper  plates  may  be  increased  by  accentua- 
ting the  contact  of  tlieir  periphery  with  the  mucous  membrane.  A 
judicious  alteration  of  the  face  of  the  cast  to  effect  this  purpose  is  not 
only  permissible,  but  is  indicated  in  many  cases.  Tt  should  be  done 
as  follows:  the  cast  should  be  compared  with  the  mouth  and  the  plate 
outline  drawn  upon  it  as  described  above.  Then  the  tissue  underly- 
ing the  periphery  of  the  proposed  plate  should  be  carefully  examined 


Fig.   364 


A.  Full  upper  cast  showing  hard  areas  heavil,\-  shaded  and  snft  areas  lightly  shaded.  B.  Full 
upper  cast  showing  hard  median  ridge,  with  lines  drawn  to  show  size  of  three  layers  of  tin  foil 
to  be  added  for  purposes  of  retention. 


digitally  to  estimate  its  compressibility.  This  is  to  determine  how 
much  it  may  be  safely  compressed  by  the  margin  of  the  plate.  In 
some  mouths  the  mucous  membrane  around  the  buccal  and  labial 
alveolar  walls  is  so  dense, or  thin,  or  closely  adherent  to  the  underlying 
bone,  that  it  will  bear  only  .slight  compression,  while  in  others  it  is 
soft  and  may  be  compressed  perceptibly  without  protest.  The  cast 
(Fig.  364),  should  be  slightly  scraped  along  the.se  corresponding  areas, 
so  that  when  the  plate  has  been  formerl  upon  it,  or  upon  a  die  made 
from  it,  the  contact  of  the  plate  margins  will  be  accentuated.  The 
amount  to  be  removed  from  the  cast  is  slight  even  in  cases  requiring 
the  greatest  alteration,  and  around  the  buccal  and  labial  walls  never 
exceeds  i-r^  to  -^  of  an  inch  in  thickness.  Acro.ss  the  palatal  vault 
at  the  posterior  margin  a  greater  amount  may  be  removed;  proportion- 
ately, twice  as  great  as  that  taken  off  elsewhere.  This,  of  course,  is  with 
the  exception  that  the  hard  median  ridge  must  not  be  pressed  upon 


AIDS  TO    THE  RETENTION   OF   UPPER   PLATE  DENTURES.      393 

uiuliily  by  the  plate,  and  it  is  best  not  to  scrape  the  cast  at  this  point 
when  the  ridge  is  inchided  in  the  outHne. 

It  is  the  custom  of  some  to  raise  a  well-defined  bead  around  the  per- 
iphery of  the  plate.  F'or  the  molded  bases  this  is  done  by  forming  a 
groove  in  the  cast  with  a  spoon-shaped  excavator  just  within  the  line 
marking  the  plate  outline  after  the  method  of  Dr.  \V.  vStorer  How.^ 
This  cannot  be  accomplished  in  a  similar  manner  for  a  swaged  plate, 
since  the  plate  could  not  be  swaged  satisfactorily  into  a  groove  of  this 
sort.  The  same  result  is  obtained  by  soldering  a  half-round  wire  (about 
gauge  IS)  to  the  periphery  of  the  palatal  surface  of  the  plate.  In  either 
case  the  bead  may  be  trimmed,  if  it  is  found  after  trial  that  it  presses 
too  hard  upon  any  part  of  the  tissue. 

The  rationale  of  the  action  of  this  measure  in  maintaining!  adhesion 
is  as  follows:  the  plate  is  drawn  into  place  by  pressure,  and  by  the  with- 
drawal of  the  air  beneath  its  surface  through  suction  produced  by  the 
tongue  and  throat  muscles.  When  all  the  air  has  been  withdrawn  and 
the  plate  adheres  to  the  surface,  the  tissues  around  tlie  periphery  are 
slightly  compressed.  As  they  are  elastic  and  tend  to  assume  their  normal 
position,  they  follow  the  margin  of  the  plate,  as  it  is  pressed  awav 
from  them  under  stress,  and  thus  maintain  for  a  greater  time  the 
contact  of  the  margins.  In  course  of  time  under  the  continued  pressure 
of  the  margins,  the  tissue  underlying  them  becomes  absorbed,  and  this 
elasticity  is  lost,  but  the  plate  margins  are  then  slightly  imbedded  in  the 
membrane  and  the  ingress  of  air  is  more  difficult.  It  must  be  under- 
stood that  the  plate  should  press  but  slightly  more  around  its  periphery 
than  elsewhere,  and  it  is  not  desired  to  make  such  alterations  in  the  cast 
that  the  plate  covering  the  other  portions  of  the  mouth  is  held  off  by 
the  contact  of  its  periphery.  This  would  make  a  vacuum-chamber  of 
the  whole  plate,  a  result  not  to  be  desired. 

The  adhesion  between  a  plate  and  the  mucous  membrane  would  be 
a  comparatively  simple  matter  if  they  were  two  flat  and  unyielding 
surfaces.  As  it  is,  the  surfaces  are  irregular,  and  one,  that  of  the  mucous 
membrane,  offers  varying  resistance  to  pressure  over  the  different  por- 
tions of  its  surface.  This,  of  course,  is  due  to  both  the  density  of  the 
membrane  and  to  the  amount  of  tissue  intervening  between  it  and  the 
bone.  The  skeletal  foundation  is  hard  and  resistant,  but  the  mem- 
brane varies  normally  in  density,  and  in  abnormal  conditions  this 
variation  is  even  more  striking. 

In  a  vast  majority  of  mouths  the  median  line  of  the  upper  jaw  presents 
a  hard  ridge,  which  isdue  to  the  close  adhesion  of  the  overlving  tissue  to 
the  suture  between  the  two  maxillary  bones,  which  extends  some  distance 
forward  as  shown  in  Fig.  364,  A.  The  alveolar  ridge  is  normally  much  less 
resistant  and  its  soft  tissues  are  less  adherent  to  the  bone.  On  each 
side  of  the  median  suture  the  areas  which  occupy  the  posterior  half  of 
the  vault  are  softer  than  any  other  portions  of  the  jaw.  This  distribu- 
tion of  the  resistance  of  the  tissues  which  is  typical  of  that  found  in  most 

^  The  Dental  Cosmos  Vol.  xiv.,  p.  785. 


394 


THE  UETENTION  OF  PLATE  DENTURES. 


cases,  is  often  varied,  and  it  will  be  seen  that  there  is  never  an  equal 
resistance  to  the  pressure  exerted  upon  a  plate  over  the  whole  area 
covered  by  it,  even  in  mouths  which  are  most  favorable  for  the  use  of 
a  plate  denture. 

In  about  one  per  cent,  of  upper  jaws  there  is  a  fissure  instead  of  a  ridge 
along  the  median  line  and  in  others  this  part  of  the  mouth  is  the  seat 
of  a  hard  bony  elevation.^ 

AVhile  the  whole  area  covered  by  tlie  plate  is  more  or  less  compres- 
sible, the  soft  underlying  areas  are  the  most  so,  and  it  will  be  noted 
that  when  pressure  is  applied  to  a  plate  made  over  an  unaltered  cast 
and  accurately  fitting  the  surface,  it  will  bear  harder  upon  the  inelastic 
areas  and  may  rock  upon  them.  Thus  pressure  applied  alternately 
upon  the  plate  at  the  sites  of  the  molar  and  bicuspid  teeth  will  cause  it 
to  rock  upon  the  hard  median  ridge,  and  if  the  tissues  on  one  side  are 
compressed  until  the  other  side  is  detached  from  the  membrane,  the 


Fig.   365 


Fig.  366 


Diagram  illustrating  leverage  upon  incisors. 


Diagram    illustrating  leverage  uPon  molar. 


plate  will  drop.  It  is  evident  that  this  should  be  prevented  if  po.ssible. 
Let  us  consider  the  direction  of  the  force  usually  apj)lied  to  an  upper 
denture  and  those  forces  which  tend  to  displace  it.  During  the  use  of 
the  plate  the  force  of  mastication  is  applied  to  it  along  the  arch  of  the 
teeth,  and,  as  these  are  approximately  over  the  alveolar  ridge  or  to  its 
labial  or  buccal  side,  the  ridge  itself  is  the  portion  of  the  jaw  which 
receives  the  pressure  of  mastication.  If  the  force  was  applicfl  to  the  plate 
along  the  whole  line  of  the  teeth  uniformly  at  all  times,  as  it  is  when  the 
teeth  are  in  close  occlusion,  the  plate  would  be  firmly  pressed  into  place. 
But  it  constantly  varies  in  distribution,  amount,  and  direction,  according 
to  the  position  of  the  food  between  the  teeth.  The  pressure  received 
upon  the  incisors  tends  by  leverage  over  the  process  in  front  to  displace 
the  rear  of  the  plate  (Fig.  365),  while  that  upon  the  molars  and  bicus- 
pids, tends  to  depress  the  opposite  side  by  leverage.  (Fig.  366.)  It  is 
evident  that  an  advantage  would  be  gained  if  the  tissues  were  uniformly 
compressible,  but  this  condition  never  exists.  However,  if  the  pressure 
of  the  plate  upon  the  hard  areas  is  relieved,  and  it  is  not  permitted  to  bear 
upon  them  under  force  until  the  soft  tissues  have  been  compressed  into 


*  L.  P.  Haskell.      Items  of  Interest. 


AIDS  TO   THE  RETENTTON   OF   UPPER  PLATE  DENTURES.      395 

a  like  resistance,  the  same  object  will  be  accomplished.      It  is  possible 
to  construct  a  plate  which  will  do  this. 

The  most  satisfactory  way  to  effect  this  result  is  by  making  additions 
at  the  site  of  the  hard  areas  to  the  cast  upon  which  the  plate  is  to  be 
made.  A  cast  made  from  a  plaster  impression,  which  accurately  rep- 
resents the  hard  and  soft  areas  alike,  no  compression  of  the  latter 
having  occurred  in  securing  the  impression,  is  compared  with  the 
mouth,  and  the  hard  areas  having  been  located  by  a  careful  digital 
examination,  are  relieved  on  the  cast  by  additions  to  its  surface. 
When  the  plate  is  to  be  made  directly  upon  the  cast,  as  in  vulcanite 
work,  the  additions  may  be  most  exactly  made  of  layers  of  tin  foil  No. 
60,  cut  to  size,  and  laid  on  to  the  necessary  thickness,  usually  about 
three  layers  being  required.      These  are  made  to  adhere  with  liquid 

Fig.  367 


Very  flat  upper  jaw  in  which  plate  retention  is  difficult. 

silex.  On  a  cast  to  be  used  as  a  model  for  a  die,  wax  may  be  used  for 
this  purpose.  The  standard  of  compressibility  ought  to  be  the  normal 
alveolar  ridge  in  which  the  tissues  are  healthy  and  supported  by  bone. 
The  hardest  areas  are  to  be  covered  most  thickly,  that  along  the  median 
line  in  an  upper  jaw  being  usually  the  one  requiring  most  attention 
Bony  tuberosities  in  the  median  line,  as  in  Fig.  364,  B,  or  those  located 
elsewhere  should  always  be  relieved  in  this  way.  Some  operators 
prefer  to  accomplish  this  end  by  scraping  from  the  impression  at  these 
points,  but  this  does  not  seem  so  desirable  a  procedure,  for  the  reason 
that  it  is  more  difficult  to  judge  of  the  amount  taken  from  a  surface  than 
of  that  added  to  a  surface,  particularly,  inasmuch  as  in  the  method 
above  described,  the  thickness  of  the  additions  may  be  always  measured. 
As  there  are  areas  harder  than  our  standard  of  compressibility,  so 
there  are  areas  softer,  but  these  do  not  concern  us  except  as  they  are 
located  at  places  at  which  the  force  of  mastication  is  received.  The 
soft  area  in  the  posterior  third  of  the  vault  on  either  side  of  median 
line  does  not  need  any  compression  by  the  ordinary  plate,  although 
the  contact  of  the  edge  of  the  plate  therewith  should  be  accentuated. 


396  THE  RETENTION   OF  PLATE  DENTURES. 

The  alveolar  ridge  itself  is  quite  soft  in  some  cases,  the  tissues  being 
spongy  and  flabby  and  easily  compressible.  (Fig.  SOT) .  This  condition 
frequently  results  where  the  teeth  have  been  lost  through  pyorrhcpa  al- 
veolaris,  the  alveolar  process  having  been  considerably  absorbed  before 
the  teeth  are  finally  lost,  leaving  a  very  low  ridge  covered  with  a  thick 
mass  of  soft  tissue.  This  condition  of  softness  is  also  frecjuently  met 
with  in  the  anterior  portion  of  the  upper  jaw,  where  absorption  of  the 
alveolus  under  a  plate  denture  has  been  caused  by  the  impact  of  the 
natural  lower  front  teeth,  the  lower  molars  and  bicuspids  having  been 
lost  and  the  whole  work  of  mastication  thrown  upon  the  anterior  teeth 
and  the  plate. 

It  is  evident  that  it  is  a  serious  disadvantage  to  have  soft  compres- 
sible tissues  underlying  the  plate  at  the  very  position  at  which  the  force 
of  mastication  is  received,  and  it  is  in  these  cases  that  it  is  most  difficult 
to  obtain  firm  retention.  The  soft  tissues  yield  under  pressure,  per- 
mitting the  plate  to  bear  upon  the  harder  portions  of  the  vault  with  a 
consequent  tilting  and  dropping. 

The  measures  usually  employed  to  combat  this  condition  are  the 
alteration  of  the  face  of  a  cast  which  accurately  represents  the  hard 
and  soft  tissues  in  their  normal  relation,  or  the  taking  of  an  impression 
of  the  jaw  with  some  material  re(|uiring  force  in  its  application  which 
shall  compress  the  soft  tissues  and  thus  yield  a  cast  with  these  tissues 
compressed  as  they  should  be  under  the  plate.  In  the  first  of  these 
measures  the  cast  is  scraped  or  carved  at  portions  corresponding  to  the 
soft  areas  W'ith  a  view  to  representing  them  as  compressed  under  the 
plate.  This  requires  much  judgment,  but  with  care  a  satisfactory  re- 
sult may  be  obtained  in  cases  in  which  only  the  alveolar  ridge  or  certain 
parts  of  it  are  soft.  The  cast  is  compared  to  the  tissues  and  the  carving 
done  only  after  a  careful  estimate  of  the  amount  to  be  removed. 

The  methods  of  taking  the  impression  to  obtain  a  cast  representing 
the  soft  tissues  compressed  are  described  in  Chapter  VII.  It  must  be 
remembered  that  in  addition  to  compressing  the  soft  structures  of  the 
ridge,  there  is  danger  of  also  displacing  them,  and  this  must  l)e  guarded 
against,  or  must  be  remedied  by  an  alteration  of  the  cast.  The  soft  gum 
tissue  is  pressed  outward  as  the  impression  material  is  carried  home, 
and  the  cast  must  be  slightly  scraped  on  the  buccal  or  labial  aspect  of 
this  soft  portion  of  the  ridge.  Each  of  these  measures  is  open  to  the 
objection  of  inaccuracy,  but  a  full  recognition  of  the  danger  which  might 
result  from  improper  alteration  of  the  cast  and  a  careful  examination  of 
the  mouth  in  comparison  with  the  cast  and  the  making  of  alterations 
to  accord  therewith,  will  sometimes  warrant  the  procedure.  It  is  seldom 
possible  to  depend  upon  this  measure  as  the  only  one  to  promote  the 
retention  of  the  denture,  and  it  must  be  supplemented  in  most  instances 
by  the  addition  of  a  vacuum-chamber,  but  in  cases  of  this  type  the  retention 
is  so  difficult  that  advantage  should  be  taken  of  every  means  to  pro- 
mote it. 

It  has  been  recommended  in  very  difficult  cases  of  this  character,  in 
which  the  whole  alveolar  ridge  is  covered  with  a  pendulous  mass  of 


ATMOSPHERIC  PRESSURE.  397 

soft  tissue,  that  this  be  removed  surgically  under  cocaine  anaesthe- 
sia. This  course  is  the  indication  where  adhesion  cannot  be  obtained 
without  it,  and  it  may  be  said  that  the  adjustment  of  the  plate  will  in  a 
large  number  of  cases  be  simplified  by  such  an  operation. 

ATMOSPHERIC  PRESSURE. 

Atmospheric  pressure  is  utilized  in  the  retention  of  upper  plate  dent- 
ures by  the  partial  exhaustion  of  the  air  from  a  space  made  for  this 
purpose  in  the  portion  of  the  plate  in  relation  with  the  mucous  mem- 
brane. This  space  is  known  as  the  vacuum-chamber.  The  principle 
has  been  in  use  in  dentistry  for  a  long  period  of  time,  the  first  recorded 
instance  of  its  use  in  the  United  States  being  that  of  W.  H.  Gilbert,  a  con- 
fectioner of  Hartford,  Conn.,  in  1840.  A  vacuum-chamber  of  some- 
what different  form  was  patented  by  Dr.  John  A.  Cleveland  of  Charles- 
ton, S.  C,  in  1850. 

The  partial  exhaustion  of  the  air  from  the  vacuum-chamber  causes 
the  pressure  of  the  atmosphere  upon  the  lingual  surface  of  the  plate  to 
sustain  it  in  situ  upon  the  jaw.  The  air  is  withdrawn  from  the  cavity 
by  the  patient  by  the  use  of  the  tongue  and  throat  muscles.  A  partial 
vacuum  is  created  in  the  portion  of  the  mouth  just  back  of  the  plate  and 
the  air  is  drawn  out  from  beneath  it.  It  is  estimated  that  with  the 
greatest  exhaustion  of  air  which  it  is  possible  to  obtain  in  a  vacuum- 
chamber  three-quarters  of  an  inch  square  in  area,  the  sustaining  force  is 
equivalent  to  about  two  and  one-half  pounds  pressure.  The  vacuum 
can  never,  of  course,  be  perfect  and  it  is  believed  that  in  a  large  majority 
of  cases  the  air  in  the  chamber  is  only  very  slightly  rarefied. 

The  use  of  the  vacuum-chamber  principle  has  been  the  subject  of 
considerable  discussion  in  dentistry,  some  practitioners  having  great 
faith  in  its  permanent  utility,  whereas  others  believe  that  its  use  is  but 
temporary  and  uncertain,  and  consider  its  attendant  disadvantages  to 
greatly  outweigh  its  usefulness.  It  is  argued  by  the  opponents  of  the 
principle  that  in  course  of  time  the  mucous  membrane  is  drawn  into 
the  depression  in  the  plate,  thus  wholly  or  partially  obliterating  it,  and 
in  consequence  destroying  the  utility  of  the  device.  They  also  argue 
that  the  irritation  of  the  soft  tissues  caused  by  the  pressure  of  the  edge 
of  the  vacuum-chamber  and  that  occurring  over  the  area  covered  by 
the  chamber,  are  serious  drawbacks  to  its  use. 

The  advocates  of  this  principle  maintain  that  in  the  beginning  the 
adhesion  of  all  upper  plate  dentures  is  increased  by  the  use  of  the  cham- 
ber; that,  even  if  it  is  of  only  temporary  utility,  the  stability  of  the  den- 
ture thus  acquired  tides  the  patient  over  the  period  in  which  he  or 
she  is  getting  accustomed  to  the  fixture.  They  also  argue  that,  despite 
the  drawing  of  the  mucous  membrane  into  the  space,  this  cavity  is  never 
completely  filled  up,  and  it  is  always  possible  to  get  some  pressure  from 
the  atmosphere  in  consequence.  They  further  add  that  a  space  located 
over  the  areas  ordinarily  hard  in  most  mouths  produces  a  relief  of  the 
pressure  of  the  plate  at  these  points. 


398  THE  RETENTION  OF  PLATE  DENTURES. 

Dr.  L.  P.  Haskell,  of  Chicago,  lends  the  force  of  his  opinion  against 
the  employment  of  the  vacuum-chamber,  believing  that  this  device  is 
never  necessary,  and  that  just  as  firm  retention  can  be  obtained  by  a 
moflification  of  the  cast  to  relieve  the  pressure  upon  the  hard  areas. 
Dr.  Haskell's  vast  experience  entitles  his  view  to  the  most  profound 
respect. 

The  vacuimi-chamber  has  become  too  well-established  a  principle  in 
dentistry  to  ])elieve  that  it  will  ever  be  entirely  abandoned.  It  probably 
has  a  certain  field  of  usefulness  and  this  is  gauged  by  a  balancing  of  its 
evident  advantages  and  disadvantages  in  favor  of  the  former.  To 
obtain  the  most  satisfactory  results  from  its  use,  careful  attention  must 
be  paid  to  the  detail  of  its  form  and  location,  and  to  the  avoidance  of  all 
measures  which  tend  to  emphasize  its  attendant  disadvantages. 

The  following  method  of  its  location  is  quoted  from  Burchard: 
"  The  slight  movement  usual  with  a  plate  during  mastication  tends 
to  separate  it  from  the  mucous  membrane  and  permit  the  access  of  air 
to  its  under  surface. 

"The  line  of  least  movement,  as  the  movement  is  lateral,  a  rocking 
from  side  to  side,  is  along  the  median  line  of  the  vault;  and,  as  the 
concavity  of  the  hard  palate  is  usually  of  an  irregular  vault  form,  the 
point  of  least  movement  is  near  its  apex.  If  the  movement  does  not 
extend  to  an  edge  of  the  chamber,  the  stability  of  the  plate  is  not 
materially  affected,  but  when  one  of  these  edges  loses  its  contact,  air 
enters  the  chamber  and  adhesion  is  destroyed. 

"The  more  closely  the  edges  of  the  chamber  approximate  this  line 
the  less  tendency  to  disturbance  there  is,  so  that  comparatively  narrow 
chambers  are  to  be  preferred;  but  the  depression  should  be  of  sufficient 
size  to  not  materially  lessen  the  effects  of  a  partial  vacuum.  Naturally 
the  chamber  should  be  in  the  area  of  greatest  stability,  that  of  least 
movement.  This  area  will  be  found  around  and  about  the  centre  of 
gravity,  and  in  shape  resembling  the  outlines  of  the  dental  arch." 

There  should  be  a  general  correspondence  in  the  size  of  the  vacuum- 
chamber,  and  the  palatal  vault  and  its  outline  should  carefully  follow 
the  general  outline  of  the  alveolar  ridge.  It  is  desirable  as  far  as  pos- 
sible that  the  distal  edge  shall  not  be  laid  down  in  very  soft  tissue,  nor 
should  the  anterior  edges  impinge  forcibly  upon  the  rugse.  Fig.  368 
illustrates  how  the  form  of  the  vacuum-chamber  should  correspond  to 
that  of  the  alveolar  ridge. 

The  vacuum-chamber  should  inclose  within  its  area  any  hard  bony 
elevation  which  may  be  found  along  the  median  line  of  the  vault,  pro- 
vided this  would  not  carry  the  edges  of  the  chamber  too  close  to  the 
posterior  margin  of  the  plate,  or  make  the  chamber  unduly  large. 
Where  a  chamber  is  to  be  used  in  a  mouth  with  a  hard  median  ridge, 
the  form  illustrated  in  Fig.  369,  B,  is  recommended  by  many  practi- 
tioners. The  edges  of  such  a  chamber  are  nearest  to  the  line  of  least 
movement  of  the  plate,  and  the  hard  median  ridge  is  relieved. 

In  order  to  be  effective  the  edges  should  be  square  but  not  sharp. 
Unless  there  is  a  positive  contact  between  them  and  the  mucous  mem- 


ATMOSPHERIC  PRESSURE.  399 

brane,  the  air  will  readily  obtain  ingress  into  the  partially  exhausted 
chamber.  On  the  other  hand,  they  should  not  be  so  sharp  or  promi- 
nent as  to  cause  irritation  of  the  membrane  from  pressure.     The  sides 

Fig.  368 


Casts  with  plate  outline- and  form  of  vacuum-chamber  marked  upon  them. 

of  the  chamber  should  extend  in  lines  perpendicular  to  the  tissue  upon 
which  the  edges  rest. 

The  most  serious  evil  consequences  follow  the  use  of  chambers  which 


Fig.  369 


A.  Vacuum-chamber  form  fixed  in  position  upon  upper  cast,     B.  Long  vacuum-chamber  form  for  use 
in  mouth  with  Ions  hr.rd  median  rids?- 

are  too  deep  or  too  large.  It  has  been  found  by  experience  that  in  the 
softest  mouths  the  air  chamber  should  be  slightly  deeper  than  those  in 
mouths  with  firm  and  resistant  tissue.  The  vacuum-chamber  for  the 
soft  mouth  should  not  be  approximately  thicker  than  Xo.  14  (B  and 


400  THE  RETENTION  OF  PLATE  DENTURES. 

S  gauge),  while  tliat  for  a  hard  mouth  should  uot  exceed  gauge  16  in 
thickness. 

The  vacuum-chaml)er  will  l)e  found  useful  in  all  cases  in  which  the  an- 
terior alveolar  ridge  is  very  soft  without  a  corresponding  softness  of  the 
palatal  vault  and  distal  j)ortions  of  the  ridge.  It  may  be  used  to  ad- 
vantage in  very  flat  mouths  of  all  sorts.  It  should  be  used  in  all  tem- 
porary plates  where  the  labial  portion  of  the  plate  is  omitted,  the 
artificial  teeth  resting  directly  upon  the  gum.  It  is  also  of  service  in  the 
retention  of  all  partial  upper  dentures  not  held  in  place  by  means  of 
clasps. 

To  form  the  chamber  in  a  vulcanite  plate  any  vacuum-cluunber  form, 
cut  out  of  chamber-metal,  may  be  applied  to  the  cast.  Chamber-metal 
consists  of  a  sheet  of  lead  with  tin  f(nl  on  either  side;  thus  it  has  the 
softness  and  pliability  of  lead, while  its  surface  is  protected  from  the 
action  of  sulfur  in  vulcanizing  by  the  coating  of  tin.  Having  been 
cut  to  proper  shape  the  form  is  burnished  to  the  surface  of  the  cast  and 
held  in  place  by  three  pins  inserted,  one  at  its  apex  and  one  at  each  of 
its  distal  corners.  In  the  preparation  of  the  cast  as  a  model  for  a  die, 
the  air-chamber  form  is  put  in  of  w^ax.  The  ordinary  base-plate  wax 
as  supplied  by  the  manufacturers  is  thick  enough  for  the  shallowest 
air-chamber,  while  the  thickest  requires  an  addition  of  about  half  a 
layer.  This  is  pressed  into  place  and  made  to  adhere  by  means  of 
melted  wax.  The  point  of  juncture  of  the  periphery  of  the  vacuum- 
chamber  form  and  the  cast  should  be  so  distinct,  that,  when  the  plate 
is  produced,  this  edge  representing  the  edge  of  the  vacuum-chamber 
will  be  well  defined. 

Spiral  Springs. — Spiral  springs  are  seldom  used  as  a  means  of  main- 
taining artificial  dentures  in  place  at  the  present  time  because  they  have 
been  largely  succeeded  by  the  other  measures  discussed  in  this  chapter. 
The  earliest  springs  were  of  whalebone,  which  were  followed  by  those 
of  steel,  and  finally  they  were  made  of  gokl.  La  Forge  de\ased  the 
coiled  spring  wdiich  is  the  most  desirable  type  for  use.  They  are 
open  to  the  serious  objection  that  it  is  almost  impossible  to  keep  them 
clean,  and  they  are  generally  productive  of  an  irritation  of  the  adjacent 
soft  tissues  of  the  cheeks.  There  remain,  however,  a  few  cases  in  which 
other  means  of  retention  are  inapplicable,  and  in  which  spiral  springs 
must  be  used.  These  are  chiefl>'  cases  in  which  through  disease  or 
surgical  operations  the  form  of  the  jaw  is  so  altered  that  any  sort  of 
adhesion  is  impossible.  There  are  also  a  few  cases  of  extremely  flat 
mouths  or  greatly  contracted  jaws  in  which  the  use  of  spiral  springs  is 
necessary. 

Care  should  be  taken  that  their  point  of  attachment  is  correctly 
located  or  they  will  have  a  tendency,  when  the  mouth  is  open,  to  displace 
the  dentures  upon  their  base  or  even  to  protrude  them  through  the  lips. 
These  points  must  be  ascertained  by  trial,  the  usual  point  in  the  upper 
jaw  being  opposite  the  second  bicuspid  and  in  the  lower  jaw  between  the 
first  molar  and  the  second  bicuspid.  These  points  of  attachment  should 
be  at  least  seven-eighths  of  an  inch  apart  in  a  vertical  direction.  The 
spring  should  be  two  inches  long.     The  detail  of  the  construction  of  the 


THE  RETENTION  OF  FULL  LOWER  DENTURES.  401 

spiral  springs  and  of  their  attachment  is  given  in  former  editions  of  this 
book  and  many  other  older  text-books.  Their  present  infrequent  use 
renders  a  description  of  their  mode  of  construction  unnecessary  here. 

THE    RETENTION  OF  FULL  LOWER  DENTURES. 

Full  lower  dentures  are  maintained  in  situ  by  their  weight  and  by  ad- 
hesion. The  latter  is  not  of  great  value  in  a  majority  of  cases,  but  acts 
to  a  greater  or  less  extent  in  all.  The  former  is  the  most  important 
of  the  active  forces  of  retention,  but,  as  in  the  upper  jaw,  the  plate  must 
be  freed  as  far  as  possible  from  all  displacing  influences  due  to  faulty 
articulation  and  incorrect  plate  outline.  Lower  plates  are  more  subject 
to  displacement  through  the  movement  of  adjacent  tissues  than  are 
upper  plates,  and  especial  care  should  be  devoted  to  establishing  cor- 
rect outlines  for  them. 

Full  lower  dentures  are  the  most  difficult  of  all  types  of  dentures  for 
the  patient  to  learn  to  use,  as  they  have  the  least  mechanical  aid  to  re- 
tention of  all  plates.  They  are  chiefly  held  in  place  by  the  tongue,  cheek, 
and  lip  muscles,  and  every  measure  tending  to  assist  the  patient  in 
acquiring  facility  in  using  them  should  be  carried  out. 

Plate  Outline  for  Full  Lower  Dentures. — In  making  the  plate  outline 
for  a  full  lower  denture  the  same  general  principle  of  avoidance  of 
movable  tissue,  as  obtained  in  the  upper  jaw,  is  to  be  followed.  The 
muscular  structures  attached  to  the  mandible  around  the  periphery  of 
the  proposed  plate  are  located  at  a  level  relatively  higher  than  in  the 
upper  jaw.  The  tissues  attached  to  the  labial  and  buccal  surfaces  of 
the  mandible  are  placed  at  a  higher  level  than  those  attached  to  its  lin- 
gual aspect.  The  plate  outline  should,  therefore,  be  sufficiently  above 
the  point  of  reflection  of  the  mucous  membrane  to  avoid  any  possible 
movement  transmitted  through  this  tissue.  The  muscular  structures 
to  be  avoided  are  the  attachment  of  the  levator  labii  inferioris,  the  de- 
pressor anguli  oris,  the  buccinator,  and.  the  muscles  of  the  floor  of  the 
mouth.  The  frsenum  of  the  tongue  must  be  given  full  play,  and  it  is 
desirable  to  avoid  the  plicse  of  mucous  membrane  around  the  external 
border  of  the  plate,  those  most  commonly  found  existing  opposite  the 
canine  and  bicuspid  teeth.  The  outline  for  a  typical  case  is  shown  in 
Fig.  370,  A,  while  that  for  a  case  in  which  there  has  been  great  resorp- 
tion of  the  process  is  shown  in  Fig.  370,  B. 

The  plate  outline  for  the  full  lower  denture  should  be  carefully  tested 
when  the  bite  is  taken,  by  requesting  the  patient  to  touch  the  roof  of  the 
mouth  with  the  tongue  and  noting  the  impingement  of  the  plate  upon 
the  tissues  on  the  lingual  side  of  the  jaw.  k  stretching  of  the  lip  and 
cheek  tissues  upward  by  means  of  the  thumb  and  forefinger  of  one  hand, 
the  other  hand  holding  the  plate  in  situ  to  counteract  any  displacing 
force  which  this  may  develop,  will  enable  the  operator  to  judge  of  the  im- 
pingement in  these  regions.  It  is  impossible  in  some  instances  to  en- 
tirely free  the  plate  from  the  influences  of  moving  tissue,  but  the  eftort 
should  be  made  to  reduce  this  to  the  minimum. 

26 


402  THE  RETENTION  OF  PLATE  DENTURES. 

Gravity. — The  force  of  gravity  is  of  service  in  tlie  retention  of  all 
lower  plates,  whether  full  or  partial,  being  the  chief  physical  force  which 
maintains  full  lower  dentures  in  place.  A  recognition  of  the  part  played 
by  it  in  the  maintenance  of  lower  dentures  has  led  to  the  construction 
of  dentures  characterized  by  considerable  weight  for  very  flat  mouths 
in  which  retention  is  difficult.  This  object  is  efi'ected  in  the  use  of 
so-called  "weighted  rubber"  for  lower  vulcanite  dentures  and  the  use 
of  metallic  dentures  of  all  forms,  fast  metal  dentures,  cast  metal 
base-plate  with  vulcanite  attachment,  swaged  metal  plates  with  soldered 
teeth  and  with  vulcanite  attachment,  and  continuous-gum  dentures 
all  possess  the  advantage  of  considerable  weight. 

In  the  case  of  a  very  flat  mouth,  as  is  shown  in  Fig.  370,  B,  the  use  of 
a  weighted  lower  denture  is  frequently  advisable.     It  must  be  remem- 


A.  Plate  outline  for  full  lower  cast  with  well-defined  ridge.     B.  Plate  outline  for  full  lower  east  with 

little  ridge. 

bered,  however,  that  the  weighting  of  a  denture  should  not  be  carried  to 
the  point  that  it  is  burdensome  to  the  patient.  The  author  has  seen 
a  case  where  extreme  weight  has  so  stimulated  the  absorption  of  the 
bone  that  the  mandible  had  become  very  thin  and  dangerously  liable  to 
fracture.  This  contingency  must,  of  course,  be  avoided.  The  use  of 
weighted  dentures  is  entirely  confined  to  full  cases,  as  partial  lower 
cases  should  receive  sufficient  maintenance  from  the  natural  teeth. 


THE  RETENTION  OF  PARTIAL  DENTURES. 

Partial  Upper  Dentures. — These  are  maintained  in  place  by  adhesion, 
by  atmospheric  pressure,  and  by  clasps. 

Adhesion  is  of  service  to  a  greater  or  less  extent  in  all  cases,  but  it 
cannot  alone  be  depended  upon:  its  chief  utility  is  in  conjunction  with 
atmospheric  pressure.  It  is  manifest  that  in  j)artial  cases  the  easy  access 
to  the  palatal  surface  of  the  plate  which  the  spaces  about  the  natural 
teeth  afford  to  the  air,  makes  adhesion  a  less  eftecti^'e  means  of  retention 


THE  RETENTION  OF  PARTIAL   DENTURES.  403 

than  in  full  cases.  When  the  plate  is  held  in  place  upon  the  mucous 
membrane  by  atmospheric  pressure  through  a  \-acuum-cavitY  or  by 
clasps,  adhesion  between  the  plate  and  the  membrane  supplements 
the  other  retentive  means.  In  most  partial  upper  cases,  therefore,  where 
advantage  may  be  taken  of  the  position  of  the  posterior  margin  of  the 
plate,  the  contact  of  this  is  to  be  accentuated  by  scraping  the  caist  as  in 
full  upper  dentures.  This,  of  course,  has  to  be  done  advisedly  and  only  in 
those  instances  in  which  the  margin  rests  upon  comparatively  soft  tissue. 

Contact  of  the  plate  with  the  natural  teeth  just  above  their  gingivae 
serves  to  stay  it  and  maintain  it  in  place  under  the  stress  of  mastication. 
This  contact  also  serves  to  prevent  the  pinching  of  the  membrane  be- 
tween the  edges  of  the  plate  and  the  teeth,  and  should  always  be  estab- 
lished, except  those  cases  in  which  the  insertion  and  removal  of  a  plate 
thus  made  would  be  prevented  because  of  the  contours  or  inclination 
of  some  of  the  teeth;  in  such  instances  the  plate  must  be  cut  away  to 
permit  its  easy  placement.  In  this  latter  class  of  cases  provision 
must  be  made  to  prevent  the  edge  of  the  plate  from  sinking  into  the 
mucous  membrane  about  the  teeth  not  touched  by  it,  by  the  employ- 
ment of  lugs  attached  to  the  clasps  and  resting  upon  the  occlusal  surface 
of  the  teeth  as  described  in  Chapter  XIV.  Advantage  is  taken  of  the 
bracing  or  staying  effect  of  natural  teeth  by  the  use  of  half-clasps  or 
stays  attached  to  the  plate  and  placed  to  grasp  the  tooth  or  teeth  in 
such  a  way  as  to  resist  the  displacing  force. 

Atmospheric  pressure  is  to  be  preferred  in  most  cases  as  the  means  of 
retention  of  partial  upper  dentures.  Exception  to  this  occurs  when  the 
configuration  of  the  vault  and  the  consistence  of  the  tissues  is  unfavor- 
able to  this  means,  and  in  those  cases  in  which  its  use  would  unduly 
extend  a  plate  carrying  only  a  few  teeth.  In  some  cases,  as  of  those 
supplying  the  posterior  teeth,  it  is  the  only  available  means  of  retention. 
Where  it  is  to  be  employed,  the  vacuum-chamber  is  to  be  located  and 
shaped  in  accordance  with  principles  already  outlined  for  full  dentures. 

Clasps  as  a  means  of  supporting  partial  upper  dentures  are  discussed 
later  in  this  chapter,  while  the  details  of  their  construction  and  mode  of 
attachment  are  given  in  the  chapter  on  Swaged  Metal  Plates. 

Plate  Outline  for  Partial  Upper  Dentures. — In  marking  the  outline 
for  a  partial  upper  case  it  is  advisable  to  draw  it  so  that  the  edge  of  the 
future  plate  is  just  in  contact  with  the  cervical  margins  of  the  teeth. 
Teeth  which  are  to  be  clasped  must,  of  course,  have  sufficient  room  about 
them  for  the  placing  of  the  clasp.  Single  isolated  teeth  in  the  distal  part 
of  the  mouth  are  to  be  included  in  the  plate  outline,  its  buccal  edge 
being  made  continuous,  and  the  plate  carried  around  them,  unless,  as 
the  last  molars  in  the  series,  they  would  cause  the  plate  to  extend  too 
far  back.  Then  the  plate  abuts  upon  them,  as  in  the  anterior  part 
of  the  mouth. 

At  the  site  of  the  artificial  teeth  when  they  are  to  rest  upon  the  gum 
as  in  the  anterior  part  of  the  mouth,  in  cases  where  little  resorption  has 
occurred,  the  plate  is  only  to  extend  up  to  the  tooth  and  not  under  it, 
except  in  partial  metal  plates  where  a  tongue  of  the  plate  should  underly 


404  THE  RETENTION  OF  PLATE  DENTURES. 

one-half  of  the  portion  of  the  tooth  in  rehition  with  the  process  as  de- 
scribed in  Chapter  XIV.  In  the  distal  part  of  the  mouth  where  the 
teeth  are  not  so  visible  in  the  movements  of  the  lips,  the  plate  should 
extend  up  as  high  on  the  outside  of  the  process  as  the  movable  tis- 
sues will  permit,  the  same  principles  obtaining  as  for  full  dentures.  It 
is  usual,  when  the  teeth  back  of  the  canine  are  to  be  supplied,  to  per- 
mit the  first  bicuspid  to  rest  upon  the  gum,  the  buccal  margin  of  the 
plate  ascending  from  the  second  bicuspid. 

The  location  of  the  posterior  margin  of  the  plate,  which  determines 
its  size,  is  to  be  settled  by  the  number  of  the  teeth  it  is  to  carry,  and  by 
the  locations  of  the  remaining  natural  teeth.  If  the  plate  is  to  be  re- 
tained by  atmospheric  pressure,  the  posterior  margin  must  be  laid  down 
in  comparatively  soft  tissue,  and  the  plate  must  be  large  enough  to 
admit  of  properly  placing  the  vacuum-chamber.  If  clasps  are  the 
retentive  device,  the  plate  area  may  be  markedly  decreased,  and  the 
reader  is  referred  to  Chapter  XIY.  for  a  discussion  of  this  feature. 

Retention  of  Partial  Lower  Dentures. — These  are  retained  in  place 
mainly  by  gravity  and  by  contact  with  the  remaining  natural  teeth, 
usually  through  the  instrumentality  of  clasps.  Lower  dentures  cover 
so  small  a  plate  area  that  adhesion  plays  little  part  in  their  retention. 
Because  of  their  small  plate  area  it  is  necessary  that  every  measure  be 
taken  which  will  assist  in  maintaining  the  plate  upon  its  proper  resting- 
place.  This  fact,  together  with  that  of  the  known  difficulty  attending 
the  use  of  full  lower  dentures,  should  indicate  the  importance  of  retaining 
all  natural  teeth  in  the  lower  jaw  which  might  be  utilized  to  stay  the 
plate  even  for  a  short  period. 

A  partial  lower  denture  can  be  advantageously  equipped  with  clasps 
in  nearly  every  case.  These  are  intended  chiefly  to  maintain  it  in  place 
upon  its  supporting  base,  but  occasionally  they  must  be  designed  to 
transmit  some  of  the  force  of  mastication  to  the  natural  teeth.  Thus, 
for  example,  a  denture  supplying  all  the  posterior  teeth  often  exhibits 
a  tendency  to  move  backward  in  use,  and  clasps  attached  to  the  natural 
teeth  adjoining  the  vacant  spaces  on  either  side  should  be  arranged  to 
prevent  this  movement.  In  cases  of  this  kind  where  a  natural  second 
or  third  molar  remains  in  the  mouth,  the  plate  abuts  upon  this  and  the 
backward  tendency  of  the  plate  is  obviated. 

Far  greater  liberty  is  permissible  in  the  way  of  contact  of  the  plate 
and  clasps  with  the  natural  teeth  in  the  lower  jaw  than  in  the  upper 
jaw.  In  the  former  case  the  fact  that  the  teeth  are  bathed  to  a  greater 
extent  in  the  saliva,  which  by  reason  of  gravity  is  more  plentiful  about 
them  and  thus  the  acid  products  of  fermentation  and  bacterial  activity 
are  more  quickly  neutralized,  renders  this  contact  less  harmful  to  the 
teeth. 

Plate  Outline  for  Partial  Lower  Dentures. — For  partial  lower  plates 
the  margin  of  the  denture  is  to  be  determined  according  to  the  following 
method:  the  plate  should  rest  upon  the  remaining  natural  teeth  for 
the  maintenance  and  slight  additional  support  which  is  thereby  gained. 
In  the  front  of  the  mouth  the  plate  outline  is  to  be  marked  half  way  up 


THE  RETENTION  OF  PARTIAL  DENTURES.  405 

the  lingual  surfaces  of  the  teeth,  tlie  remainder  of  the  periphery  of  the 
plate  being  determined  as  for  full  dentures  by  the  location  of  the 
movable  tissue.  A  single  isolated  tooth  perpendicular  to  the  ridge  is  to 
be  included  in  the  plate  outline,  the  buccal  margins  being  continuous 
and  an  opening  made  in  the  plate  to  receive  the  tooth. 

The  high  attachment  of  the  tissue  of  the  cheeks  upon  the  buccal  sur- 
face of  the  mandible  makes  it  usually  necessary  to  have  the  buccal 
margin  of  the  plate  relieved  at  this  point.  Experience  has  demon- 
strated that  this  edge  of  a  plate  made  upon  an  unaltered  cast  has  a 
tendency  to  bury  itself  in  the  tissue.     It  is,  therefore,  advisable  in  many 


A 

Diagram   illustrating   addition   to   lower   cast. 

full  lower  cases  and  in  all  partial  lower  cases  to  make  an  addition  to  the 
cast  along  this  line  as  represented  in  Fig.  371. 

Where  the  summit  of  the  alveolar  ridge  is  represented  as  being  sharp 
and  thin,  it  is  advisable  to  relieve  the  plate  somewhat  at  this  point  by 
making  an  addition  to  the  cast.  This  permits  the  plate  to  have  its 
point  of  bearing  on  the  sides  of  the  ridge  instead  of  upon  its  summit. 
Fig.  371  illustrates  the  manner  of  making  this  alteration. 

CLASPS. 

"  Clasps^  are  metallic  bands  partially  encircling  the  crowns  of  natural 
teeth,  and  serving  as  a  means  for  the  retention  of  artificial  dentures. 
Tiie  employment  of  the  device  is  prompted  by  necessity,  and  not  by 
choice.  In  upper  plates  they  are  employed  where  the  vacuum-chamber 
is  found  to  be  insufficient  to  retain  a  denture  in  position,  where  the 
configuration  of  the  vault  renders  the  chamber  inapplicable,  or  where 
the  positions  of  the  replaced  teeth  render  the  covering  of  the  vault  with 
a  large  plate  unwarrantable.  They  are  attached  to  partial  lower  den- 
tures to  prevent  displacement  by  the  movements  of  the  tongue,  cheeks, 
and  lips,  and  by  the  forces  to  which  these  pieces  are  subjected  during 
mastication. 

The  great  advantage  of  the  employment  of  clasps  is  an  increased 
stability  of  the  piece,  the  disadvantage  is,  if  worn  long  enough,  they 
eventually  cause  the  loss  of  the  crown  of  the  tooth  clasped,  through 
chemical  solution,  and  mechanical  abrasion.  The  food-deposits  beneath 
and  about  the  clasp  are  the  seat  of  lactic  fermentation,  so  that  a  gradual 
solution  of  the  crown  by  lactic  acid  occurs,  if  the  clasps  are  not  kept 
in  an  aseptic  condition. 

'  Burchard:  American  Text-Book  of  Prosthetic  Dentistry,  Second  Edition. 


40()  Till-:  RF.THSTloy    OF  PLATE  DF.STrilF.S. 

Not  infrecjueiitly  tlie  teetli  are  so  mechanically  strained  I)}'  the  force 
of  mastication  transmitted  through  the  clasps,  that  the  rt-tentive  appa- 
ratus of  the  teeth  succumbs  and  the  teeth  are  dislodged.  The  latter  is 
a  more  serious  consideration  than  the  loss  of  a  crown;  an  artificial 
substitute  for  the  latter  may  be  provided  and  serve  for  clasping,  but 
loosened  teeth  are  the  heie  noir  of  dentistry.  This  danger  is  lessened 
by  accuracy  of  adaptation  of  the  plate,  and  by  having  the  clasps  of 
sufficient  elasticity  to  yield  to  stress  and  diminish  the  strain  on  the 
teeth. 

Clasps  properly  adapted  serve  but  to  stay  a  plate,  not  to  support  it. 
The  support  should  be  derived  from  uniform  pressure  upon  the  soft 
tissues ;  the  clasps  are  an  adjunct  preventing  displacement.  The 
violation  of  this  principle  is  responsible  for  many  of  the  ills  attributed 
to  the  wearing  of  clasps. 

In  selecting  teeth  to  be  clasped,  where  a  selection  is  possible,  they 
should  be  chosen  with  a  regard  to  their  form,  the  position  and  condition 
of  the  tissues  of  the  teeth,  and  the  surrounding  parts." 

In  the  upper  jaw  the  most  satisfactory  tooth  to  afl'ord  attachment 
for  a  clasp  is  the  first  molar.  Its  location,  strength,  and  shape  are  es- 
pecially favorable  to  its  use  for  this  purpose.  Next  in  order  come  the 
second  bicuspid,  second  molar,  and  first  bicuspid.  The  disadvantageous 
position  of  the  third  molar,  its  shortness,  and  irregular  shape  render  it 
seldom  of  use  for  clasping,  though  sometimes  it  may  be  the  only  depend- 
ency and  must  be  used.  Only  in  extreme  cases  should  the  upper  canine 
be  clasped,  and  even  less  frequently  the  central  and  lateral  incisors. 
These  teeth  are  all  poorly  shaped  for  clasping,  besides  being  weaker  than 
the  distal  teeth,  and  in  addition  the  displayal  of  a  gold  clasp  about  them 
is  objectionable.  When  it  is  necessary  to  clasp  the  canine,  the  clasp 
should  be  shaped  and  located  to  appear  as  a  cervical  gold-filling  in  the 
tooth. 

In  the  lower  jaw  the  teeth  most  commonly  used  for  clasp  purposes  are 
the  bicusjjids,  as  these  frequently  adjoin  the  vacant  spaces  to  be  supplied 
by  the  plate  and  are  most  satisfactory  for  this  purpose.  The  first 
molar  has  the  advantage  of  strength  and  favorable  shape,  but  is  less 
frequently  used  because  its  presence  in  the  mouth  either  indicates  a  case 
in  which  the  molars  back  of  it  alone  are  missing — a  case  in  fact  in  which 
it  is  doubtful  if  the  advantage  gained  by  supplying  these  few  teeth  com- 
l)ensates  for  the  trouble  of  wearing  it,  experience  proving  such  plates 
unsatisfactory — or  it  may  mean  a  case  with  teeth  anterior  to  the  first 
molar  missing  in  which  bridgework  would  be  greatly  preferred. 

If  possible  two  teeth  on  opposite  sides  of  the  mouth  should  always  be 
selected  for  clasping,  so  located  that  a  line  drawn  from  one  to  the  other 
would  pass  through  the  centre  of  the  plate,  if  it  be  an  upper  denture, 
and  if  it  be  a  lower  plate,  they  should  be  located  to  be  of  the  greatest 
mechanical  support.  In  difficult  lower  cases  even  a  single  central  in- 
cisor may  be  clasped  to  advantage,  thus  serving  to  hold  the  plate  on  the 
alveolar  ridge,  and  hence  greatly  aiding  the  patient  in  acquiring  the  use 
of  the  denture. 


CHAPTER  XII. 

THE  SELECTION,  ARRANGEMENT,  AND  ARTICULATION  OF  ARTIFICIAL 

TEETH. 

By  Charles  R.  TurxVer,  D.D.S.,M.D. 

In  a  general  way  it  may  be  said  that  the  objects  of  artificial  dentures 
are  the  restoration  of  the  impaired  functions  and  the  altered  facial  ap- 
pearance which  have  ensued  from  the  loss  of  the  natural  teeth.  Artificial 
dentures  should  restore  any  lost  parts  of  the  mechanism  concerned  in 
the  preparation  of  food  for  subsequent  stages  in  its  digestion,  or  should 
establish  a  satisfactory  means  for  the  execution  of  this  function.  If 
the  normal  voice  and  articulate  speech  have  been  impaired  by  the  loss 
of  the  teeth,  the  dentures  should  restore  these  by  providing  a  substitute 
for  the  lost  tissues  concerned  in  the  sound  production,  and  they  should 
impose  no  impediment  to  the  proper  exercise  of  these  functions.  They 
should  restore  the  lost  portions  of  the  apparatus  by  w'hich  the  expressive 
movements  of  the  face  are  produced,  and  not  interfere  with  the  normal 
operation  of  these  activities;  and  finally,  they  should  restore  the  facial 
contours  and  the  fixed  expression  of  the  face,  and  provide  such  sub- 
stitutes for  the  missing  tissues  in  those  portions  of  the  mouth  which  are 
exposed  to  view  in  laughter  or  speech,  as  shall  be  in  harmony  and  accord 
with  the  other  features  of  the  face.  In  addition,  they  must  be  con- 
structed with  the  view  of  utilizing  to  the  best  advantage  the  materials 
at  command, and  in  consonance  with  such  sound  mechanical  principles 
as  will  insure  the  efficiency  of  the  appliance. 

To  design  a  denture  which  shall  successfully  meet  these  requirements 
demands  an  acquaintance  with  the  normal  operation  of  the  impaired 
functions,  a  recognition  of  the  alterations  which  have  been  produced 
by  the  loss  of  the  teeth,  and  a  knowledge  of  the  materials  and  principles 
which  may  be  best  adapted  for  the  restoration  of  these  functions. 
Furthermore,  the  placing  of  an  artificial  denture  is  to  be  regarded  as  a 
rational  therapeutic  measure,  in  which  the  requirements  of  each  in- 
dividual case  are  recognized,  and  the  appliaince  designed  and  constructed 
to  meet  the  indications  thereof. 

Here  follows  a  tabulated  list  of  the  ends  to  be  subserved  by  artificial 
dentures,  together  with  the  factors  concerned  with  promoting  these 
ends. 

r  (  1 .  Physical  means  of  retention. 

A.  Stability  of  the  plate.  \  2.  Correct  plate  outline. 
/  3.  Correct  articulation  of  teeth. 

B.  Functional  efRciency    j  1.  Form, 
of  the  teeth.  '   (  2.  Arrangement. 


I.  Food  preparation 


f  1.  Strength  of  teeth. 
■Mr    -u      ■     1    ai   ■  12.  Strength  of  base-plate. 

Mechanical  efficiency  j  3   ^^^^^^^  relation  of  teeth 


of  plate  and  teeth. 


to  base-plate  to  resist 
stress. 

407 


408  SELECTION,  ARRANGEMENT,   AND  ARTICULATION. 

TT    ,.  .  ,  ,     (  A.   Form,  position  ;iii(l  ainmi'ciiK'iit  of  teeth. 

II.  \oice  and  speech,  j  j^     p^,^^^  ^\^j  1;,,^,,,.^,  eontoursof  plate. 


III. 


IV. 


Express!  \e 
movements 
of  face. 


Facial 

expression. 


A.  Positions  of  the  teeth. 

H.    Form  and  labial  contours  of  the  plate. 

C.   Relation  estal)lished  l>et\veen  the  jaws. 


r 


Facial  con- 
tours. 


H.  Teeth  as  fea- 
I  tin-es  of  the 

[  face. 


1.  1-ips. 

2.  Cheeks. 
.3.  Relation  !)e-  "l 

tween  jaws.     ( 

1.  Color." 

2.  Form. 

3.  Relative  positions. 

4.  Gums. 


Positions  of  teeth, 
liuccal    and  labial 

contours    of    the 

plate. 


These  factors  will  be  discussed  in  detail  from  the  standpoint  of  the 
principles  underlying  their  correct  adaptation  to  the  individual  ca.se. 
They  will,  however,  be  considered  under  headings  somewhat  different 
from  the  above,  .since  many  of  these  factors  are  concerned  with  both 
the  utilitarian  and  cosmetic  purposes  of  the  plate,  and  besides  avoid- 
ing unnecessary  repetition,  the  method  selected  seems  to  afford  the 
simplest  means  of  elucidating  the  subject. 


Fig.  372 


Casts  arranged  upon  articnlatur,  with  liitc-philos  removed. 

The  design  of  artificial  dentures  to  effect  the  various  purposes  above 
outlined,  includes  the  selection,  arrangement,  and  articulation  of  the 
teeth,  and  the  arrangement  of  the  plate  form  and  contours.  The 
technique  of  denture  construction  using  the  various  bases  will  be  de- 
scribed in  succeeding  chapters. 

Many  of  the  data  which  are  to  be  used  in  the  process  have  been  ob- 
tained from  the  patient  at  the  time  the  bite  is  taken,  and  it  is  supposed 
that  the  casts  have  been  mounted  properly  upon  the  articulator,  and 
that  the  bite-plates  have  been  laid  aside  for  reference.     (Fig.  372.) 


THE  SKLECTION  OF  ARTIFfCIAL    TEETH.  '  409 

THE  SELECTION  OF  ARTIFICIAL  TEETH. 

Suitable  artificial  teeth  for  use  in  the  vast  majority  of  cases  which 
the  prosthetist  is  called  upon  to  treat  may  be  obtained  by  a  judicious 
selection  from  the  stock  of  the  manufacturers,  which  it  has  been  said 
in  Chapter  III.,  is  sufficiently  comprehensive  to  meet  most  of  the  needs 
of  the  present  day.  The  teeth  selected  will,  in  most  instances,  require 
some  modification  on  the  part  of  the  dentist  to  fit  them  for  the  case 
in  hand.  Details  of  these  procedures  will  be  discussed  subsequently 
in  this  chapter,  and  it  is  sufficient  to  say  here  that  the  alterations  in 
the  teeth  are  with  a  view  of  adapting  them  to  meet  the  peculiarities  of 
the  individual  case. 

The  considerations  which  determine  the  choice  in  the  selection  of 
artificial  teeth  for  a  given  case  are,  first,  anatomical:  that  they  shall 
have  the  appearance  required  of  substitutes  for  the  natural  teeth,  and 
the  form  demanded  by  their  proposed  functional  activities;  and  secondly, 
mechanical :  that  they  may  be  adapted  to  the  base  upon  which  they 
are  to  be  mounted,  and  satisfy  such  other  mechanical  demands  as  are 
incident  to  the  shape  and  relation  of  the  jaws  in  the  individual  case. 

The  physical  characters  of  the  teeth  relating  to  their  appearance  are 
determined  in  edentulous  cases  by  the  consideration  of  temperament. 
This  requires  a  diagnosis  of  the  predominating  temperamental  type  or 
combination  of  types  existent  in  the  individual.  A  careful  study  of 
the  physical  attributes  associated  with  the  basal  temperamental  types 
and  of  their  combinations  in  the  excellent  tables  of  Dr.  A.  H.Thomp- 
son, is  urged  upon  the  student,  and  a  thorough  acquaintance  with  the 
details  of  the  physical  characters  of  these  types  is  necessary.  In  gen- 
eral it  may  be  said  that, in  the  matter  of  color  of  the  artificial  teeth,  the 
complexion  of  the  individual  and  the  coloring  of  other  pigmented 
tissues  of  the  body,  are  the  guides  which  may  be  most  safely  used,  and 
that,  as  for  the  dimensional  characteristics  of  the  teeth,  the  general 
physique  and,  in  particular,  the  physical  characteristics  of  the  head  and 
face,  are  of  best  service  for  their  determination.  In  addition  to  this, 
something  more  will  be  needed  in  the  way  of  an  appreciation  of  form 
and  color,  which  will  enable  the  dentist  to  produce  a  harmonious  result. 
The  existence  of  this  harmony  in  nature,  for  the  most  part,  is  the  basis 
upon  which  the  restorations  are  made.  This  harmony  is  not,  how- 
ever, universal,  for  there  are  occasional  exceptions  to  the  principles 
which  have  long  been  established.  There  are  people  who  have  teeth 
apparently  too  small  and  of  a  color  too  light,  but  they  are  always  the 
exception,  and  for  this  reason,  attract  an  attention,  which  it  is  desired 
the  patient  with  the  prosthetic  appliance  shall  avoid. 

From  a  cosmetic  standpoint  the  end  to  be  aimed  at  first  is  the  re- 
establishment  of  the  personal  appearance  of  the  individual.  This  is 
not  always  possible,  because  the  data  which  are  at  hand  are  at  best 
not  sufficiently  complete.  Nor  is  it  in  every  case  advisable,  even  if  it 
were  possible,  for  instances  occur  in  which  the  exact  reproduction  of 
the  conditions  which  existed  before  the  loss  of  the  teeth  would  require 


410  SKLECTIOS,    ARRAyClEMENT,  AND  ARTICULATION. 

tlic  imitation  of  a  disfiguring  defect.  In  such  cases  it  may  be  said 
that  the  reproduction  of  a  condition  known  to  exist  before  the  teeth 
were  lost,  which  condition  amounted  to  a  deformity,  was  in  poor  waste, 
or  was  greatly  lacking  in  aesthetic  effect,  is  only  justifiable  when  there 
are  strong  reasons  for  perpetuating  it  as  a  means  for  preserving  phys- 
ical identity. 

1.  The  Size  and  Form  of  the  Teeth. — In  the  selection  of  teeth  for  an 
edentulous  case,  it  is  desirable  to  know  the  size  and  shape  of  the  lost 
natural  teeth  for  which  substitutes  are  required.  This  is  seldom  pos- 
sible, except  in  the  few  cases  in  which  the  prosthetist  has  extracted 
the  natural  organs,  in  which  event  they  should  be  carefully  preserved 
for  guidance  in  the  selection  of  the  artificial  teeth.  In  general  other 
means  must  be  used  for  determining  the  size  and  shape  of  the  artifi- 
cial teeth. 

Fig.  373 


Full  upper  cast,  showing  the  trial  of  artificial  teeth  of  proper  size  with  second  molar  reaching 
center  of  the  maxillary  tuberosity. 

Because  of  the  resorption  of  the  aheolar  process  and  the  consequent 
diminution  in  the  size  of  the  maxilla,  but  twenty-eight  teeth  are  used 
for  full  artificial  dentures,  the  third  molars  being  omitted.  If  the  full 
complement  of  teeth  were  used,  they  would  either  be  too  small,  or  if  of 
proper  size,  could  not  be  correctly  arranged  in  relation  to  the  process. 
The  data  which  indicate  the  combined  width  of  the  teeth  must  be  ob- 
tained from  the  casts  of  the  mouth.  When  placed  in  trial  upon  the 
upper  cast  in  that  relation  to  the  alveolar  ridge  which  it  is  proposed 
they  shall  occupy,  with  the  centrals  on  either  side  of  the  median  line, 
the  distal  side  of  the  second  molar  should  rest  upon  the  centre  of  the 
maxillary  tuberosity.  (Fig.  37.3.)  In  cases  of  extreme  resorption  of 
the  alveolar  ridge,  the  cast  alone  does  not  furnish  all  the  desired  in- 
formation, but  for  the  most  part  it  is  usual  to  judge  of  the  \yi(lth  of  the 
teeth  by  their  relation  to  the  length  of  the  upper  alveolar  ridge. 


THE  SIZE   AM)   FORM   OF  THE    TEETH.  411 

As  obtained  in  full  sets  from  the  manufacturers,  the  sizes  of  the  in- 
dividual teeth  of  a  series  are  intended  to  be  correctly  proportioned. 
The  "fronts,"  or  six  anterior  teeth,  and  the  "backs"  are  matched  to 
have  the  same  general  proportion  and  may  be  fairly  trusted  for  this. 
Cases  sometimes  present,  however,  for  which  the  size  of  the  "backs" 
may  be  increased  to  advantage,  because  the  canine  of  the  series  comes 
only  to  about  the  position  of  the  canine  eminence,  while  the  backs  do  not 
reach  the  tuberosity.  Minor  differences  in  the  proportion  of  the  back 
teeth  met  with  in  the  natural  series  need  not  be  imitated.  A'ariations 
in  the  proportionate  size  of  the  six  anterior  teeth  may, however, be  imi- 
tated to  great  advantage,  and  the  selection  of  larger  centrals  or  canines 
for  use  in  appropriate  cases  will  often  be  attended  with  happy  results. 
This  will  be  mentioned  later. 

Having  decided  upon  the  proper  width  for  the  upper  teeth,  their 
length  is  next  to  be  determined,  and  this  is  largely  decided  by  the  tem- 
peramental indications  of  the  patient,  together  with  a  purely  physical 
factor,  namely,  the  position  of  the  high  lip  line.  This  latter  landmark, 
it  will  be  remembered,  indicates  the  highest  point  to  which  the  lip  is  ele- 
vated in  smiling  and  laughter,  and  it  is  desirable  to  have  the  portion 
of  the  artificial  denture  which  is  displayed  by  these  acts  represented  by 
teeth,  unless  this  would  make  them  too  long.  However,  the  correct 
proportion  between  the  length  of  the  teeth  and  their  already 
determined  width  must  be  preserved  to  accord  with  the  predom- 
inating  temperamental  indication  of  the  patient,  and  in  no  case 
should  this  consideration  be  sacrificed.  The  mobility  of  the  upper  lip 
varies  in  individuals  and  in  some  it  may  be  elevated  so  high  as  to  dis- 
play a  good  deal  of  the  adjoining  gum  and  process.  Therefore,  this 
space  cannot  always  be  filled  in  with  the  artificial  teeth,  and  in 
cases  of  a  very  high  lip  line,  the  use  of  gum-section  teeth  is  sometimes 
justifiable.  This  will  also  be  discussed  later.  The  distance  between 
the  high  lip  line  and  the  lower  edge  of  the  bite- plate  which  corresponds 
to  the  proposed  position  of  the  cutting  edges  of  the  anterior  teeth,  should 
be  the  trial  length  of  the  artificial  teeth,  the  correct  proportioning  of 
this  length  to  the  width  in  accordance  with  the  temperamental  in- 
dication of  the  patient  should  be  the  final  deciding  factor  as  to  this 
dimension. 

The  general  form  of  the  teeth  is,  of  course,  determined  by  their  width 
and  length,  but  their  appearance  is  also  affected  by  the  character  of 
their  outline  and  their  surface.  These  are  matters  which  are  wholly 
determined  by  temperamental  indications  for  a  tabulated  list  of  which 
the  reader  is  referred  to  pages  259-262.  in  Chapter  V.  Except  in 
rare  instances  in  which  mechanical  advantage  is  obtained  by  a  differ- 
ent form  of  tooth,  as  of  those  of  protruding  jaws,  the  surface  contours 
and  outlines  of  the  teeth  should  correspond  with  the  temperamental 
indications  of  the  patient.  The  rounded  form  of  the  sanguine  temper- 
ament should  be  used  for  that  temperament,  while  the  flat  faced 
angular  tooth  with  constricted  neck  should  be  used  for  the   nervous 


412 


SELECTIOX,  ARRANGEMENT,  AND  ARTICULATION. 


(see  Fig.  374).  The  niaiiuracturcrs  siii)j)ly  a  sufficient  variety  of  molds 
for  satisfactory  selection,  but  they  also  provide  teetli  made  of  the  shade 
of  one  temperament  and  of  the  characteristic  color  of  another.  These 
are  made  largely  for  commercial  reasons  to  supply  a  demand  which 
arises  without  a  just  appreciation  of  the  harmony  desirable  in  such 
matters  and  their  use  should  be  avoided. 

2.  The  Color  of  the  Teeth. — The  most  difficult  physical  characteristic 
of  the  artificial  teeth  to  determine  is  their  color.  In  edentulous  cases 
as  has  already  been  indicated,  this  must  be  selected  upon  a  judgment 
based  upon  other  })hysical  characteristics  of  the  patient.  A  few  remarks 
upon  the  color  of  the  natural  teeth  may  not  be  out  of  place. 


Fig.  374 


fffUl     fffiM 


Four  basal  temperameutal  types  of  artificial  teeth  :  A,  bilious  ;  B,  nervous;  C,  sanguine; 

D,  lymphatic. 

The  color  of  teeth  is,  in  general,  due  to  two  things — the  intrinsic  color 
of  the  enamel  and  dentine,  and  their  proportion  and  distribution  in  a 
given  tooth.  The  intrinsic  color  of  the  enamel  and  dentine  is  in  accord 
with  that  of  the  other  pigmented  tissues  of  the  body.  It  harmonizes 
with  the  color  of  the  hair,  the  eyes,  and  in  particular  with  the  color  of 
the  skin.  This  latter  is  of  the  greatest  importance  in  determining  the 
color  of  teeth.  Ivy^  has  said  that  the  complexion  is  of  great  impor- 
tance in  deciding  the  color  of  artificial  teeth.  Joseph  Head^  has 
stated  his  belief  that  the  fundamental  color  of  the  skin  over  parts  of 
the  body  protected  from  the  sun,  and  that  of  the  teeth  is  the  same, 
and  that  if  the  pink  element  in  the  former  due  to  the  presence  of  the 
blood  were  removed  by  pressure  upon  the  part,  the  color  of  the  .skin  thus 
observed  should  be  the  fundamental  color  of  the  artificial  teeth.  The 
author  is  not  wholly  prepared  to  accept  this  view,  but  has  observed 
instances  in  which  it  was  fairly  accurate. 

The  state  of  organization  of  the  teeth  has  been  supposed  to  partly 
account  for  the  color.     It  is  certain  that  the  greater  translucency  of 


American  System  of  Dentistry.   \^ol.  ii.,  p.   1034 
In  private  conversation. 


THE  COLOR   OF  THE  TEETH.  413 

the  enamel  in  the  nervous  temperament  is  a  result  of  its  \\'\^\\  state  of 
organization,  and  accounts  in  part  for  the  blue  cutting  edge  character- 
istic of  these  teeth,  while  the  opaque  enamel  of  the  teeth  of  the  lym- 
phatic temperament  is  commonl}-  observed  to  be  of  poorer  structure. 

The  proportion  between  the  enamel  and  dentine  also  is  related  to  the 
color  of  the  teeth.  In  the  typical  lymphatic  teeth,  for  instance,  the 
opacity  of  the  enamel  and  the  fact  that  it  is  generously  backed  up  with 
dentine  partly  account  for  their  color,  while  in  the  thin  teeth  of  the 
nervous  temperament,  the  enamel  plates  at  the  cutting  edges  of  the 
incisors  enclose  little  or  no  dentine,  permit  the  light  to  be  carried 
through,  and  appear  blue  at  this  point.  Furthermore,  the  commonly 
observed  yellow  color  at  the  neck  of  incisor  teeth  is  due  to  the  thin- 
ness of  the  enamel  wdiich  permits  the  yellow  color  characteristic  of 
dentine  to  show  through. 

As  age  advances  there  is  a  deepening  in  the  shade  of  the  tooth  which 
is  due  to  a  molecular  change  in  its  tissues,  and  teeth  are  a  shade  or  so 
darker  in  middle  or  late  life  than  they  were  in  early  years. 

The  fact  has  been  brought  out  by  E.  A.  Royce^  after  a  careful  exami- 
nation of  a  large  number  of  natural  teeth  that  the  individual  members 
of  any  given  natural  set  vary  much  in  shade.  He  says,  "In  our  study  of 
this  subject  we  must  have  some  standard  by  which  to  measure  the  shade 
of  each  tooth,  and  for  this  standard  the  upper  central  incisors  of  the 
denture  under  consideration  were  always  taken.  Some  means  being 
necessary  to  convey  to  you  the  diflferent  shades  of  the  teeth  in  the 
mouth,  I  selected  0,  or  zero,  to  represent  the  shade  of  the  central  in- 
cisors, using  numerals  to  express  the  other  shades — the  higher  the 
numeral  the  darker  being  the  shade."  *  *  "The  upper  central  incisors 
are  the  lightest,  the  laterals  are  darker,  and  the  canines  are  darker  still. 
The  first  bicuspids  are  generally  lighter  than  the  canines,  and  the  sec- 
ond bicuspids  lighter  than  the  first.  The  first  molars  generally  vary 
but  a  shade  or  so  from  the  second  bicuspids." 

The  general  color  of  the  artificial  teeth  should  be  selected  to  accord 
with  the  temperamental  indication  of  the  patient  according  to  the 
tables  on  pages  259-262,  This  should  be  modified  in  shade  by  the  age 
of  the  patient,  an  individual  past  middle  life  requiring  teeth  usually  as 
much  as  tw^o  shades  (of  the  manufacturer's  shade-guide)  darker  than 
at  an  early  period  in  life.  For  reasons  of  convenience  the  shade  of 
the  teeth  should  be  selected  at  the  time  the  bite  is  taken.  The  trial 
shade  should  be  actually  tested  under  the  lips,  because,  from  the  shadow 
cast  by  the  latter,  the  teeth  will  appear  lighter  in  the  mouth.  The  same 
shade-guide  used  in  the  patient's  mouth  should  be  used,  if  possible,  at 
the  dental  depot,  because  there  are  many  slight  variations  in  teeth  said  to 
be  of  the  same  commercial  shade  which  are  due  to  details  of  molding  and 
burning,  and  these  differences  exist  in  the  sample  teeth  of  the  shade-guide. 

A  happy  effect  may  usually  be  produced  by  the  selection  of  the  an- 
terior teeth  from  different  sets,  thus  breaking  up  the  unnatural  uniform- 
ly The  Dental  Review  ,  Vol.  xv.,  pp.  301  and  934 


414 


SELECTION,  ARRANGEMENT,   AND  ARTICULATION. 


ity  in  color  observed  in  the  stock  sets.  Slightly  darker  canines  usually 
give  a  very  natural  effect  to  the  teeth,  and  frequently  the  use  of  slightly 
bluer  lateral  incisors,  and  bluer  bicuspids  will  add  to  this.  The  differ- 
ent shades  recommended  by  Royce  may  also  be  obtained  by  the  use  of 
oil  stains,  as  described  on  page  429. 

We  next  come  to  discuss  the  selection  of  teeth  in  order  that  they  may 
fulfill  the  mechanical  recjuirements  imposed  by  the  base  used,  the  re- 
lation of  the  jaws,  and  the  amount  of  resorption  of  the  process. 

3.  The  Base. — Artificial  teeth  are  constructed  with  a  means  of  attach- 
ment and  a  general  form  suitable  to  the  base  upon  which  they  are  to  be 
mounted.  Vulcanite  and  celluloid  teeth  are  similar  and  may  be  used 
interchangeably   upon  the   two  bases.     Plate  teeth  are  suitable  for 

Fig.   375 


A   Diagram  showing  the  ideal  relation  of  an  artificial  incisor  to  the  alveolar  process.     B  Diagram 
showing  the  ideal  relation  of  an  artificial  molar  to  the  alveolar  process. 


crown  and  bridge  or  metal  plate  work.  In  England  and  on  the  Conti- 
nent they  are  used  to  some  extent  for  vulcanite  work,  for  which  purpose 
they  are  made  wuth  long  pins  which  are  bent  into  a  hook  for  attachment 
to  the  base.  For  cast  dentures,  where  the  metal  is  cast  directly  about 
the  teeth,  vulcanite  teeth  are  used  and  they  are  occasionally  useful  in 
continuous-gum  dentures,  although  the  teeth  made  especially  for  this 
work  are  the  usual  indication. 

4.  The  Amount  of  Resorption  of  the  Alveolar  Process  and  the  Distance 
Between  Jaws  and  their  Relation. — In  the  mounting  of  the  artificial  teeth, 
other  things  being  equal,  it  is  desirable  to  have  their  occlusal  ends 
occupy  the  position  with  relation  to  the  alveolar  ridge  which  was  char- 
acteristic of  their  natural  predecessors.  The  incisors,  canines,  bicus- 
pids, and  molars  would  be  placed,  therefore,  over  the  alveolar  ridge, 
in  the  upper  jaw,  and  slightly  to  its  buccal  and  labial  sides.  (Fig. 
375.)  In  the  lower  jaw  the  incisors  and  canines  would  be  slightly 
to  the  labial  side  and  over  the  ridge,  while  the  line  of  teeth  then  crosses 
the  ridge,  the  last  molars  being  somewhat  to  the  lingual  side  of  its 
summit.  This  ideal  method  of  placing  is  by  no  means  always  pos- 
sible, because  of  the  state  of  resorption  of  the  process  and  the  rela- 
tion of  the  jaws.  The  proper  placing  of  the  teeth  will  be  discussed 
later  in  this  chapter,  but  inasmuch  as  they  may  be  selected  of  surh  form 


THE  AMOUNT  OF  RESORPTION. 


415 


as  to  greatly  facilitate  this,  the  mechanical  demands  upon  them  must 
be  known  at  the  time  they  are  selected,  and  the  choice  made  to  fur- 
ther this  end.  There  are  also  mechanical  requirements  incident  to 
the  strain  upon  the  tooth  in  use,  which  may  be  furthered  by  judicious 
selection. 

The  labial  surface  of  the  fronts  and  the  buccal  and  occlusal  surfaces 
of  the  backs  are  fashioned  to  meet  anatomical  demands;  other  portions 
of  the  teeth  are  designed,  as  was  seen  in  Chapter  III.,  to  meet  the  mechan- 
ical demands  above  referred  to.  As  plain  rubber  teeth  are  the  ones  in 
which  this  provision  is  best  brought  out,  they  will  be  used  to  illustrate 
the  principles. 

The  anterior  teeth  have  the  headed  pin  which  affords  attachment  to 
the  base-plate,  a  pin  guard,  which  makes  the  division  between  "the  bite" 
and  the  "shut," and  also  what  is  technically  called  "the  ridge  lap." 

Fig.   376 


Diagrammatic  drawing  showing  section  through  upper  cast  and  lower  bite-plate,  with  artifi- 
cial incisors  properly  filling  in  the  space.  The  dotted  Une  indicates  the  contom-  of  the  upper 
bite-plate. 


Other  things  being  equal,  it  is  desirable  in  full  sets  to  have  the  pins 
near  the  alveolar  ridge.  The  "ridge  lap"  is  intended  to  be  in  relation 
with  the  alveolar  ridge,  and  "the  bite"  makes  up  the  other  part  of 
the  length  of  the  tooth.  Long  bite  teeth,  it  must  be  remembered,  ase 
not  the  strongest  type  of  teeth  because  of  the  leverage  upon  them,  the 
pin  being  the  fulcrum,  the  length  of  "the  bite"  part  of  the  tooth  repre- 
senting the  power  arm.  Long  bite  teeth  are,  therefore,  not  recommended 
for  use  in  cases  demanding  great  strength  in  W'hich  other  types  will 
answer  the  requirement.  In  most  full  cases,  however,  they  may  be  used 
with  reasonable  assurance  of  sufficient  strength. 

The  upper  bite-plate  having  been  removed,  the  space  between  the  an- 
terior edge  of  the  lower  bite-plate  and  the  alveolar  ridge  is  to  be  filled 
in  with  "the  bite"  of  the  teeth  selected,  the  remainder  of  the  length  of 
the  tooth  has  to  be  made  up  in  ridge  lap.  (Fig.  376.)  Thus  when  there 
has  been  little  resorption  of  the  process  and  the  jaws  are  some  distance 


416  SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 

apart,  the  teeth  may  rest  almost  upon  tlie  v\(\gii,  and  a  tooth  with  a 
short  ridge  lap  is  selected.  (Fig.  377.)  Where  the  jaws  are  close  to- 
gether, however,  a  tooth  with  long  ridge  lap  must  be  used,  and,  of 
course,  of  short  bite,  since  in  teeth  of  a  given  length  the  ridge  lap  and 
bite  are  usually  inversely  related.  (Fig.  378.)  Where  there  has  been 
much  resorption  of  the  process  and  the  teeth  are  to  be  mounted  almost 


Fig.  3' 


Fig.  378 


Use  of  short  ridge  lap  with  small  amount  of 
resorption  of  process. 


Use  of  long  ridge  lap  with  a  short  distance 
between  the  jaws. 


upon  the  ridge,  a  short  ridge  lap  is  indicated.  (Fig.  379.)  To  avoid 
the  use  of  a  long  bite  tooth  in  a  given  case,  a  tooth  with  a  long  shut 
may  be  used,  but  it  must  be  remembered  that  the  plate  must  not  be 
made  too  thick  at  the  portions  about  the  pins,  as  it  may  interfere  with 
speech.     (Fig.  380.) 


Use  of  short  ridge-lap  tooth  with  much  resorp- 
tion of  process,  mounting  tooth  directly  over 
ridge. 


Use  of  long  shut  tooth,  with  short  ridge  lap, 
where  there  is  much  space  between  jaws  and 
little  resorption  of  the  process. 


Where  plain  teeth  are  to  be  mounted  directly  upon  the  gum,  as  in  all 
temporary  dentures,  a  short  ridge  lap  must  be  used. 

When  the  antero-posterior  relation  of  the  jaws  is  abnormal,  as  in  pro- 
truding upper  or  lower  jaw,  this  condition  may  be  accommodated  in  the 
teeth  selected.  Thus,  in  a  protruding  upper  jaw,  a  short  ridge  lap  is 
indicated  for  the  upper  teeth,  while  in  a  protruding  lower  jaw,  teeth 
with  a  long  ridge  lap  may  be  used  advantageously  in  most  instances. 


THE  AMOUNT  OF  RESORPTION. 


417 


(Fig.  381.)  In  a  protruding  upper  jaw,  too,  the  use  of  teeth  with  a  flat 
face  provides  a  means  of  making  the  protusion  less  apparent,  while  on 
the  other  hand,  when  the  lower  jaw  is  anteriorly  placed,  so-called 
"bow-faced"  teeth  will  lessen  the  apparent  protrusion  of  the  lower 
jaw  and  often  permit  a  better  arrangement  of  the  upper  and  lower 
incisors.      (Fig.  382.) 


Fig.  381 


Use   of    flat-faced  tooth  for  protruding 
upper  jaw. 


Use  of  bow-faced  tooth  for  protruding 
lower  jaw. 


In  the  bicuspid  and  molar  region,  the  adjustment  of  these  teeth  to 
the  alveolar  ridge  may  be  made  with  greater  ease.  The  use  of  teeth,  as 
long  as  the  distance  betw^een  the  ridges  will  permit  of  their  proper 
placement,  is  indicated.  This  brings  the  tooth  closely  in  relation  with 
the  ridge,  thereby  lessening  the  amount  of  base  used,  and,  if  the  amount 
of  the  tooth  above  the  pins  is  as  great  as  possible,  this  is  an  added  ad- 


FiG.  383 


Fig.  384 


Kitting  of  molar  teeth  :    filling  in  space 
between  the  ridges. 


Use  of  saddle-back  teeth  in  case  with  short 
distance  between  ridges. 


vantage,  for  in  the  articulation  of  these  teeth  it  permits  the  making  of 
the  sulci  deeper  by  grinding.  (Fig.  383.)  Cases  will  be  met  with,  how- 
ever, where  the  distance  between  the  two  alveolar  ridges  is  so  short 
that  recourse  must  be  had  to  so-called  "saddle  back"  teeth,  although 
this  is  more  especially  necessary  in  partial  dentures.     (Fig.  384.) 

The  use  of  countersunk  pin  teeth  is  only  possible  when  the  distance 
between  the  jaws  is  sufficient  to  permit  them  to  be  placed  almost  di- 

27 


418 


SELECTION,   ARRANGEMENT,   AND  ARTICULATION. 


rectly  over  the  ri(l<i;e,  in  which  instances  their  anatomical  form  will  be 
fomid  advantageous.  (Fig.  385.)  Plate  teeth  and  continuous-gum 
teeth  do  not  have  the  divisions  of  vulcanite  teeth  above  alluded  to, 
except  that  in  the  case  of  the  former  a  general  conformation  to  this 
plan  is  made  by  grinding  at  the  time  they  are  fitted,  and  they  should 
be  selected  with  this  in  view. 

The  use  of  gum  section  teeth  is  the  indication  in  some  cases,  but  the 
number  of  these  instances  is  small.  The  fixed  relation  between  the 
teeth  of  a  block  limits  their  usefulness  because  there  is  little  or  no  latitude 
in  their  arrangement.  They  are  contraindicated  in  those  cases  in 
which  little  resorption  of  the  alveolar  ridge  has  taken  place  for  the 
obvious  reason  that  they  would  cause  too  great  fulness  of  the  denture 
at  this  place.  They  are  used  to  best  advantage  in  cases  in  which  much 
of  the  denture  is  displayed  in  laughing,  as  indicated  by  the  high  lip  line, 


Fig.  385 


Fig.  386 


Countersunk  pin  teeth  set  over  ridge. 


Gum  section  filling  in  space  exposed   in 
smiling  and  laughing. 


when  the  space  between  it  and  the  lower  bite-plate  cannot  be  filled  in 
with  a  plain  tooth  without  the  use  of  one  anatomically  too  long.  (Fig. 
386.)  They,  of  course,  should  be  selected  as  regards  their  anatomical 
and  mechanical  forms  by  the  same  indications  as  prevailed  with  plain 
teeth.  The  natural  appearance  of  the  gum  portion  of  the  section,  an 
imitation  of  mucous  membrane  only  equalled  by  that  of  continuous- 
gum  work,  is  the  only  advantage  which  they  possess. 


THE  SELECTION  OF  TEETH  FOR  PARTIAL  DENTURES. 

In  the  choice  of  teeth  for  partial  dentures  the  dentist  is  greatly  aided 
by  the  remaining  natural  teeth  and  in  proportion  as  they  are  many 
or  few.  In  the  matter  of  size,  form,  and  color,  the  artificial  teeth 
should,  of  course,  correspond  with  those  in  the  mouth  as  closely  as 
expediency  in  each  case  warrants. 

In  general,  the  desired  color  of  the  artificial  teeth  may  be  obtained 
exactly  from  those  that  remain.  Difficulty  is  frequently  experienced, 
however,  in  exactly  matching  the  distribution  of  the  shades  in  the  ar- 
tificial teeth  to  those  of  the  natural,  for  the  reason  that  natural  teeth  are 


SELECTION  OF  TEETH  FOR  PARTIAL  DENTURES.  419 

not  of  uniform  sliado  from  cutting  edge  to  gingival  margin.  This  is 
due  to  the  varying  proportions  of  enamel  and  dentine,  the  thinness  of 
the  enamel  at  the  neck  of  the  teeth  permitting  the  dentine  to  gi\'e  an 
increasingly  yellow  cast  to  the  teeth  at  this  point.  Artificial  teeth  of 
different  manufacturers  have  different  proportions  of  the  "point  and 
base  "  enamels  which  give  color  to  these  regions,  and  a  perfect  matching 
from  their  stock  is  not  always  possible.  Here  the  use  of  stains  accord- 
ing to  the  method  described  later  in  this  chapter  will  be  found  very 
useful  in  obtaining  desired  results. 

Where  an  artificial  tooth  is  to  be  placed  between  two  natural  ones  of 
different  shades,  it  is  advised  that  a  tooth  intermediate  in  shade  between 
the  two  natural  teeth  be  selected  and  darker  than  the  estimated  shade 
rather  than  lighter,  since  a  tooth  a  little  too  dark  attracts  less  attention 
than  one  too  light. 

The  size  and  form  of  the  teeth  should  accord  with  those  in  the  mouth. 
As  to  the  former,  it  is  sometimes  justifiable  to  use  teeth  a  little  wider  or 
a  little  narrower  than  the  teeth  they  are  to  replace,  when  the  space 
between  the  adjoining  teeth  has  increased  or  diminished  since  the 
loss  of  the  natural  teeth.  In  the  front  of  the  mouth  where  the  teeth  are 
visible  this  must  be  done  with  extreme  care,  and  the  teeth  selected 
should  not  be  of  such  difference  in  size  as  to  attract  attention.  And  in 
the  front  of  the  mouth  also  where  movement  of  the  teeth  has  produced  a 

Fig.  387  Fig.  38S 


Partial  case  requiring  plain  teeth.  Partial  case  requiring  gum  section  teeth. 


widening  or  narrowing  of  the  space,  their  movement  to  correct  posi- 
tion by  orthodontic  means  is  frequently  advisable,  and  the  procedure 
is  attended  with  happy  results,  because  the  denture  serves  as  a  perma- 
nent retaining  appliance.  The  size  of  the  distal  teeth  and  those  in  the 
lower  jaw  in  particular,  which  are  not  visible  during  lip  movements, 
may  be  varied  with  greater  liberty.  A  common  case  of  this  sort  is  that 
in  which  three  artificial  bicuspids  are  used  distal  to  the  canine,  to  replace 
the  two  bicuspids  and  a  molar,  the  second  molar  ha^'ing  moved  for- 
ward and  closed  the  space :   often  one  bicuspid  and  a  molar  are  suffi- 


420  SELECTION,  ARRANGEMENT,   AND  ARTfCULATIOX. 

cieiit  to  fill  this  gap.  It  is  usual,  however,  to  use  an  artificial  canine 
tooth  back  of  a  natural  canine,  as  the  sudden  thickening  of  a  plate  by 
the  use  of  a  bicuspid  is  not  so  comfortable  to  the  tongue. 

The  amount  of  resorption  of  the  aheolar  ridge  is  another  factor  of 
importance  in  the  selection  of  teeth  for  partial  cases.  The  general  rule 
is  that  where  only  a  small  amount  of  resorption  has  occurred,  the  ar- 
tificial tooth  rests  upon  the  natural  gum  and  a  plain  tooth  is  used. 
(Fig.  387.)  If,  however,  the  process  has  resorbed  to  such  an  extent  that 
a  tooth  too  long  for  harmony  with  the  adjacent  natural  teeth  would  be 
necessary,  or  the  gum  contours  must  be  restored,  a  gum  tooth  ai)propri- 
ate  to  the  case  is  chosen.  (Fig.  388.)  The  manufacturers  supply  a 
variety  of  gum  sections  w^hich  may  be  used  with  much  advantage  in 
these  cases.  The  color  of  the  gum  should  be  carefully  matched  to  that 
of  the  adjacent  tissue. 

The  length  of  the  bite,  or  the  distance  between  the  jaws,  also  deter- 
mines the  kind  of  tooth  selecteil  as  to  bite  and  ridge  lap,  according  to 
the  general  principles  already  outlined  for  full  dentures. 

Short  bite  teeth  are  to  be  preferred  in  every  instance  in  which  they 
are  available,  as  teeth  are  subjected  to  greater  strain  on  a  partial  than 
on  a  full  denture,  but  partial  cases  exist  with  marked  overbite  of  the 
remaining  natural  teeth  and  then  a  long  bite  tooth  is  the  only  one  that 
can  be  used.  Where  the  overbite  is  very  great,  however,  it  is  usually 
advisable  to  use  a  plate  tooth,  even  for  vulcanite  work,  in  which  latter 
instance  a  gold  backing  is  applied,  and  a  tongue-like  projection  is  ex- 
tended into  the  plate,  making  the  plate  stronger  at  the  point  at  w^hich 
strength  is  needed. 

I.  THE  ARTICULATION  OF  THE  TEETH. 

The  Arrangement  of  the  Anterior  Teeth, 

The  objects  to  be  subserved  in  the  placement  of  the  anterior  teeth 
are  those  of  incision,  of  articulate  speech,  the  establishment  of  correct 
facial  profile  and  contours  by  their  support  of  the  lips  and  cheeks,  and 
finally,  the  securing  of  their  harmonious  relationship  as  a  feature  of  the 
face.  As  the  appearance  of  the  patient  is  chiefly  affected  by  the  upper 
anterior  teeth,  and  as  these  may  be  arranged  first  and  the  distal  teeth 
subsequently  placed  to  accord  and  properly  functionate  with  them,  it 
is  usual  to  arrange  them  first.  It  is  supposed  that  the  casts  have  been 
mounted  upon  an  articulator  capable  of  individualizing  the  movements 
of  the  mandible,  and  that  the  bite-plates  have  been  retained  for  the  data 
v/hich  they  furnish  in  the  setting  of  the  teeth. 

The  requirements  imposed  upon  the  anterior  teeth  by  their  functional 
relations  in  the  operation  of  incision  are  so  closely  related  to  the  subject 
of  plate  maintenance  that  they  may  be  considered  subsequently  when 
this  matter  is  dealt  with.  Suffice  it  here  to  say  that  the  utilitarian  and 
cosmetic  purposes  of  the  denture  are  often  in  conflict  in  the  arrange- 
ment of  these  teeth.     For  the  most  part  it  is  desirable  to  consider  as  of 


THE  ARRANGEMENT  OF  THE  ANTERIOR   TEETH.  421 

first  importance  the  requirements  of  appearance,  and  then  to  make 
such  compromise  between  these  demands  and  those  imposed  by  the 
incisive  function  as  will  subsequently  be  pointed  out  as  advisable.  In 
the  case  of  patients  well  past  middle  life,  where  the  resorj)tion  of  the 
alveolar  process  complicates  the  placing  of  the  anterior  teeth  in  such  a 
way  as  to  serve  both  the  ends  of  appearance  and  those  of  function,  it  is 
wise  to  sacrifice  tlie  former  in  favor  of  the  latter,  because  in  these  instan- 
ces the  correct  functioning  of  the  appliance  is  of  the  greater  importance. 

The  anterior  teeth  are  the  chief  ones  concerned  in  the  functional  re- 
lations of  articulate  speech,  but  it  is  commonly  true  that  when  their 
positions  satisfactorily  answer  the  other  necessary  requirements,  they 
usually  meet  the  demands  of  speech  because  of  the  ability  of  the  tongue 
to  adjust  itself  to  various  conditions.  The  function  of  speech  is  also 
largely  influenced  by  the  form  and  contours  of  the  plate,  and  these 
several  considerations  will  be  discussed  later. 

The  part  played  by  the  anterior  teeth  in  the  support  of  the  lips  in 
proper  profile  and  contour  will  also  be  discussed  under  a  subsequent 
heading. 

It  is  here  purposed  to  take  up,  first,  considerations  relative  to  the 
appearance  of  the  anterior  teeth  as  a  feature  of  the  face.  In  order  to 
serve  as  a  feature  of  the  face  which  thoroughly  harmonizes  with 
its  environment,  it  may  be  said,  in  general,  that  the  anterior  teeth 
should  answer  the  requirements  imposed  by  the  temperamental  re- 
lationship, and  should  also  accord  with  the  age  indications  of  the  case. 
Inasmuch  as  the  data  are  lacking  which  would  permit  an  exact  re- 
production of  the  appearance  of  the  natural  teeth,  the  object  sought 
should  be  to  have  the  artificial  teeth  appear  as  a  natural  endowment 
of  the  individual,  and  exhibit  evidences  of  the  changes  which  would 
have  been  present  upon  the  natural  teeth  at  the  age  of  the  individual. 
In  addition  to  these  requirements,  their  appearance  must  possess  an 
intrinsic  artistic  value.  It  would  not  be  enough,  for  instance,  to  ex- 
actly reproduce  in  the  mouth  of  a  patient  the  characteristics  of  the 
natural  teeth  of  another  individual,  selected  at  random,  though  of  sim- 
ilar age  and  temperament.  Such  a  denture  would  be  natural  looking, 
but  it  might  not  also  be  pleasing  to  the  eye.  Natural  dentures  to 
be  copied  should  have  some  artistic  value,  since  in  the  mouth  of  an 
edentulous  patient  a  denture  may  be  placed  which  accords  with  the 
age  and  temperament  indications  and  also  has  intrinsic  artistic  worth. 

In  the  arrangement  of  the  artificial  teeth,  the  purpose  is  to  imitate 
the  original  endowment  of  the  individual  and  to  imitate  the  effects 
produced  by  the  causes  which  have  operated  in  the  environment  of 
the  teeth,  and  these  effects  must  be  copied  from  the  observed  effects 
existing  in  mouths  under  similar  conditions.  We  shall  now  take  up  in 
detail  the  factors  which  contributed  to  these  several  ends.  The  ar- 
ticulated casts  and  the  bite-plates  furnish  the  data  for  the  following 
items:  the  inclination  of  the  teeth,  the  median  line,  the  position  of  the 
cutting  edge  of  the  teeth,  the  curve  of  the  arch,  the  support  of  the 
lips,  and  the  antero-posterior  relation  of  the  jaw. 


422  SELECTION,  ARRANGEMENT,   AND  ARTICULATION. 

1.  The  Color,  Size  and  Form  of  the  Individual  Teeth.— These  have 
been  determined  hy  their  selection,  as  already  described. 

2.  The  Relation  to  the  Lips.— The  proper  relation  of  the  teeth  to  the 
lips  largely  contributes  to  the  beailty  of  the  teeth  as  a  feature  of  the  face. 
The  most  beautiful  cases  are  those  in  which  the  cutting  edges  of  the 
upper  anterior  teeth  project  but  very  slightly  below  the  lower  margin 
of  the  upper  lip.     (Fig.  389.)     In  some  cases  the  natural  teeth  have 

Fio.    3^9 


Drawing  showing  ideal  relation  of  artificial   teeth  to  the  lips. 

been  so  much  abraded,  or  are  so  situated  that  they  do  not  reach  the 
margin  of  the  lip,  while  in  other  instances  their  edges  extend  much 
below  this  line.  In  moot  edentulous  cases  it  is  advisable  to  es- 
tablish the  teeth  in  the  first  of  these  relationships.  (Fig.  390.)  With  this 
end  in  view,  the  occlusal  surface  of  the  upper  bite-plate  has  been  trim- 
med to  a  distance  one-sixteenth  of  an  inch  below  the  lower  margin  of 
the  upper  lip  and  represents,  therefore,  the  position  of  the  cutting 
edges  of  the  anterior  teeth.  The  general  line  of  cutting  edges  is  also 
parallel  with  the  line  of  separation  between  the  lips,  a  datum  likewise 
furnished  from  the  bite-plate. 

In  the  setting  up  of  the  teeth,  the  upper  plate  should  be  removed  and 
laid  aside  for  reference.  The  correct  distance  between  the  jaws  is 
preserved  by  means  of  a  set  screw  on  the  articulator,  or  by  measuring 
the  distance  between  fixed  points  on  the  upper  and  lower  casts  with 
calipers  before  the  upper  l)ite-plate  is  removed.  The  calipers  are  laid 
aside  and  should  be  preserved  for  reference. 

3.  The  Median  Line. — The  median  line  of  the  mouth  having  been 
marked  on  the  casts,  determines  the  position  of  the  division  between 
the  upper  central  incisors  which  are  the  first  teeth  to  be  put  in  place. 
Their  cutting  edges  should  be  in  relation  with  the  outer  edge  of  the 
occlusal  surface  of  the  lower  bite-plate.     (Fig.  391.) 


iyCLL\ATION  TO   THE  RIDGE.  423 

4.  Inclination  to  the  Ridge. — The  inclination  of  the  lonfj;  axes  of  the 
teeth  to  the  alveoUir  ridjje  has  been  largely  determined  by  the  lower 
portions  of  the  labial  surface  of  the  bite-plate.     These  portions  of  the 

Fig.   390 


Six  upper  anterior  teeth  in  position  and  in  proper  relation  with  lower  bite-plate.     Side  view. 


Fig.   391 


Six  upper  anterior  teeth  in  place,  central  incisors  being  on  each  side  of  the  median  line. 

Front  view. 

bite-plate  were  made  to  support  the  lips  properly,  and  the  anterior 
teeth  must  be  so  placed  that  their  labial  surfaces  occupy  the  position 
of  the  labial  surface  of  the  bite-plate. 

The  teeth  support  and  give  form  to  the  lip,  but  in  addition,  their  in- 
clination to  the  ridge  affects  their  appearance.     This  must  be  some- 


424  SELECTION,   ARRANGEMENT,   AND  ARTICULATION. 

times  made  to  accord  with  the  demands  imjjoscd  l)y  the  functional 
purposes  of  the  denture.  After  tlu;  anterior  teetli  liave  been  set  up 
their  inchnation  sliould  accord  with  that  observed  for  teeth  of  similiar 
shape  in  jaws  similarly  related. 

The  teeth  of  a  normal  or  ideal  denture  in  jaws  having  a  correct 
antero-posterior  relation  are  inclined  about  as  follows:  the  long  axes 
of  all  of  the  anterior  teeth  are  inclined  slightly  outward  from  a  verti- 
cal plane,  the  angle  made  with  the  vertical  varying  from  a  slight  di- 
vergence to  a  considerable  amount.  The  long  axes  of  the  central 
incisors  slightly  diverge  from  the  sagittal  plane  of  the  body.  Those  of 
the  laterals  diverge  slightly  more,  wdiile  those  o'f  the  canines  are  more 
nearly  vertically  located.  Where  the  lower  jaw  is  distally  related  to 
the  upper,  the  upper  teeth  often  incline  slightly  backward,  while  where 
the  lower  jaw  is  protruding,  the  upper  anterior  teeth  are  usually 
inclined  outward,  the  lower  teeth  having  a  lingual  inclination  from 
the  pressure  of  the  lips. 

5.  The  Curve  of  the  Arch. — The  arch  formed  by  the  cutting  edges  of 
the  anterior  teeth  should  be  in  accord  with  that  which  is  characteristie 
of  the  temperament  of    the  patient.     This  is  judged  in  part  from  the 

Fro.  392 


Curve  of   tlie  anterior  teeth  in  four  ilcntures. 


outline  of  the  alveolar  process  when  the  bite-plate  is  made,  and  the  curve 
on  the  occlusal  surface  of  the  bite-plate  should  be  assumed  by  the 
teeth  when  they  are  set  up.    (Fig.  392.) 

6.  The  Relative  Position  of  the  Teeth. — In  the  ideal  or  typical  nor- 
mal   denture,  the   anterior  teeth    occupy   definite   relative    positions. 


RELATIVE  POSIT  fox  OP'   THE   TEETH.  425 

Their  cutting  edges  are  arranged  in  the  arc  of  a  circle  and  they  are 
placed  regularly  and  symmetrically.  This  condition  obtains,  however, 
in  nature  in  a  comparatively  small  proportion  of  cases,  an  irregular 
alignment  or  a  dissimilarity  between  the  two  sides  of  the  arch  being  the 
rule  rather  than  the  exception.  In  the  arrangement  of  the  anterior 
artificial  teeth,  due  cognizance  should  be  taken  of  this  state  of  affairs. 
In  the  effort  to  make  an  irregular  alignment  assume  a  natural  appear- 
ance, the  relationship  which  exists  in  natural  dentures  between  the 
alignment  of  the  teeth  and  their  form,  and  the  temperament  of  the  indi- 
vidual should  be  recognized.  In  the  tables  prepared  by  Dr.  A.  H. 
Thompson,  in  Chapter  V.,  will  be  seen  what  this  relationship  is  in  the 
basal  temperamental  types  and  in  the  binary  compounds,  and  this  gen- 
eral principle  should  be  followed  in  the  determination  of  the  relative 
positions  of  the  teeth  for  a  given  case.  It  w^ould  be  manifestly  out  of 
place  to  arrange  the  teeth  irregularly  for  a  patient  of  a  temperament  in 
which  the  arrangement  is  commonly  regular.  Furthermore,  any  irreg- 
ularity imitated  should  be  that  which  observation  has  shown  to  be  asso- 
ciated with  the  teeth  and  temperament  of  such  cases.  It  should  also 
be  borne  in  mind  that  age  has  an  influence  in  the  production  of  irreg- 
ularities of  the  anterior  teeth  through  causes  which  operate  subsequent 
to  the  original  positioning  of  the  teeth.  Attention  should  be  given 
to  the  association  between  the  irregularities  imitated  and  the  antero- 
posterior relation  of  the  jaws,  and  in  all  instances  the  general  relation 
between  cause  and  effect  should  be  borne  in  mind,  and  results  estab- 
lished to  accord  with  probable  operating  causes. 

The  regular  alignment  of  the  natural  teeth  has  been  described.  This  is 
to  be  established  v,  ith  artificial  teeth  in  mouths  of  patients  of  a  temper- 
ament of  which  this  is  characteristic,  as,  for  instance,  in  those  of  the  lym- 
phatic temperament.  It  should  be  reproduced  also  for  younger  patients 
and  those  in  w'hose  mouths  regularity  of  the  teeth  would  be  in  accord 
with  regular  and  symmetrical  features  of  the  face.  On  the  other  hand, 
irregularities  of  the  teeth  are  to  be  imitated  in  the  mouths  of  young 
patients  of  the  nervous  temperament,  since  the  natural  teeth  in  these 
mouths  are  frequently  irregularly  aligned. 

The  irregularities  of  the  anterior  teeth  commonly  observed  are  those 
with  the  long  axis  of  the  tooth  departing  from  its  position  in  the  ideal 
form  of  the  denture,  and  irregular  positions  of  the  occlusal  edges  of  the 
teeth. 

The  following  may  be  advantageously  imitated  in  appropriate 
cases:  (Fig.  393.) 

1.  Rotation  of  the  centrals  with  their  distal  surfaces  labially  placed. 

2.  Rotation  of  centrals  with  their  distal  surfaces  lingually  placed. 

3.  One  central  overlapping  the  other  with  laterals  overlapping. 

4.  Elongate   centrals. 

5.  Overlapping  laterals. 

6.  Alteration  in  position  of  the  long  axes  of  the  teeth. 

7.  Centrals  slightly  lingually  inclined. 


42fj  SELECTION,   ARRANGEMENT,  AND  AIlTICrLATION 


The  lower  teeth  are  irregularly  placed  fre(}iioiitly  as  follows: 

1.  Centrals  with  the  distal  surfaces  turned  outward. 

2.  Rotation  of  the  lateral  incisors. 

3.  Overlapping  of  laterals  or  centrals, 

4.  Overlapping  of  one  or  both  canines. 


Dentures  sh(jwing  irregular  position  of  the   anterior  teeth. 

Spaces  do  not  exist  between  the  teeth  of  a  natural  denture  without 
some  abnormal  operating  cause.  Their  existence  is  usually  a  defect 
in  the  beauty  of  the  denture,  and  the  imitation  of  this  in  artificial  teeth 
is  seldom  justifiable,  unless  it  be  in  imitation  of  a  condition  known  to 
have  existed  in  the  mouth  of  the  patient. 

7.  The  State  of  Wear  of  the  Teeth. — One  of  the  defects  commonly 
observed  in  artificial  dentures  is  that  the  teeth  are  inserted  without  an 


THE   STATE    OF    WEAR    OF    THE    TEETH. 


427 


Fig.  395,  A 


Denture  showing  imitation  of  first  degree  of  wear. 


alteration  of  their  occlusal  surfaces  to  imitate  that  ijroduced  by  the 
wearing  of  the  teeth  from  use.  In  Chapter  V.,  the  question  of  the  wear- 
ing of  the  teeth  was  considered  at  some  length.  Artificial  teeth  should 
be  matle  to  accord  with  the  probable  state  of  wear  of  the  teeth  of  the 
patient.  The  wear  on  the  teeth  in  a  natural  denture  is  determined 
partly  by  the  temperament, 
the  form  of  the  teeth,  and 
the  manner  of  movement 
of  the  mandible  peculiar 
to  the  individual.  While 
not  directly  related  to  the 
age,  it  must  be,  in  some 
measure,  in  accord  with  it, 
or  the  length  of  ser\'ice 
which  the  denture  has 
seen. 

It  is  seldom  advisable 
to  imitate  greater  degrees 
of  wear  than  the  second, 
as  further  wearing  is  of 
seldom  occurrence  under  the  conditions  of  modern  ci^■ilization  and  is 
infrequently  observed  in  the  natural  teeth. 

It  is  seldom  the  case  that  an  artificial  denture  is  required  in  a 
patient  so  young  that,  had  the  natural  teeth  ^-emained,  no  evidences 
of  wear  would  have  existed.  In  any  but  the  youngest  patients 
the  cutting  edges  of  the  incisors  should  be  ground  with  a  corundum 
wheel  to  portray  this  evidence  of  their  use,  and  the  amount  of  wear 

should  be  graduated 
from  a  slight  alteration 
of  the  cutting  edges  to 
that  observed  in  the 
second  degree  of  wear 
in  which  the  dentine 
is  exposed.  What  may 
be  considered  typical 
cases  are  illustrated  in 
Fig.  395,  and  in  the 
imitation  of  this  con- 
dition the  relation  of 
cause  and  effect,  as 
above  alluded  to,  must 
be  constantly  borne  in  mind.  To  illustrate  in  detail  one  case  which 
may  be  taken  as  a  fair  sample,  Fig.  395,  A,  presents  the  conditions 
which  might  reasonably  exist  in  a  natural  denture  of  a  patient  about 
thirty-five  years  of  age.  The  forward  movement  of  the  lower  jaw 
has  caused  the  wearing  of  the  upper  incisors  into  slight  depressions 
where  thev  were  in  contact  with  the  lower  teeth.     The  lower  teeth  have 


Fig.  395 


Denture  showing  imitation  of  second  degree  of  wear. 


428 


SELECTION,   ARRANGEMENT,   AND  ARTICULATION. 


similarly  worn.  Fig.  iiil"),  B,  shows  a  case  in  wliicli  there  has  been 
considerable  over  bite  of  the  incisors,  where  the  upper  teeth  have  been 
worn  at  the  expense  of  the  lingual  plate  of  the  enamel,  the  lower  teeth 
at  the  expense  of  the  labial.  Fig.  ;i9()  shows  a  case  of  the  second 
degree  of  wear  which  might  be  found  in  the  month  of  a  patient  aged 
fifty  years,  where  the  cus})s  have  worn  down  sufficiently  to  permit  the 
mantlible  to  move  forward,  producing  an  edge-to-edge  bite,  with  the 
comjilete  obliteration  of  the  occlusal  ends  of  the  teeth,  the  exposure  of 
the  dentine,  and  a  slight  chipping  of  the  enamel.  Other  typical  cases 
of  wear  in  natural  dentures  may  be  observed  l)y  the  dentist  and  im- 
itated in  a  similar  manner. 

It  is  suggested  by  Dr.  A.  DeWitt  Gritman  that  the  grinding  of  the 
incisors  and  the  canines  in  the  first  degree  of  wear  be  deferred  until  the 
denture  is  completed  and  tried  in  the  mouth  of  the  patient. 

8.  Recession  of  the  Gums. — This  condition,  when  of  a  physiologic 
nature,  is  seldom  observed  in  the  mouths.of  patients  younger  than  thirty- 


FiG.  39G 


Denture  showing  imitation  of  recession  of  tlie  fiiims. 


five  years  of  age,  although  it  is  p^ogressi^'e  by  almost  imperceptil)le 
degrees  up  to  this  time.  It  is  seen  most  frequently  in  patients  of  the 
sanguine  and  bilio-sanguine  temperaments.  Pathological  recession 
of  the  gums,  attended  with  an  exposure  of  the  cementum  and  a  thicken- 
ing of  the  gingival  margin,  with  a  disappearance  of  the  gum  occu- 
pying the  interproximal  space,  is  frequently  seen  in  these  patients  at 
a  later  period  in  life  and  mav  be  imitated  to  advantage  in  such  cases. 
(Fig.  39b.) 

9.  Individual  Peculiarities.  Defects  in  the  teeth  of  a  denture,  which 
have  assumed  the  form  of  an  individual  peculiarity,  are  often  to  be  re- 
produced in  the  mouths  of  patients  in  which  they  are  known  to  have 
existed.  The  defects  are  those  of  form  or  structure.  In  the  mouths 
of  patients  of  the  nervous  temperament  with  delicately  shaped  teeth, 
filling  operations  have  usually  been  necessary  before  the  time  at  which 
a  plate  denture  is  required,  and  in  such  cases,  the  insertion  of  fillings 


TINTING   AND  STAINING   PORCELAIN  TEETH.  429 

in  the  anterior  teeth  is  a  measure  which  frequently  adds  to  the  nat- 
ural appearance  of  the  denture. 

Where  a  prominent  gold  filling  has  existed  in  a  natural  tooth,  it 
may  be  reproduced  in  the  artificial,  and  will  tend  to  preserve  the  iden- 
tity of  the  individual,  in  which  cases  it  is  the  indication. 

The  lateral  incisors  are  usually  the  first  oral  teeth  requiring  filling 
operations,  and  in  those  cases  in  which  fillings  are  inserted  for  purposes 
of  naturalness,  and  without  a  history  of  their  former  existence,  these 
teeth  should  be  selected  to  receive  them.  In  the  insertion  of  the  filling 
regard  should  be  paid  to  its  placement  in  a  position  in  which  carious 
cavities  commonly  occur.  A  gold  filling  on  the  mesial  surface  of 
either  or  both  laterals  or  upon  the  mesial  or  distal  surfaces  of  either 
central  will  answer  these  several  requirements,  and  in  all  cases  the  re- 
lation of  cause  and  effect,  the  latter  represented  by  the  filling,  should 
be  borne  in  mind. 

Discoloration  of  the  teeth  is  another  condition  to  be  imitated  to  ad- 
vantage in  selected  cases.  One  condition  to  be  imitated  is  the  stain- 
ing  of  the  cervical  third  of  the  labial  surface  of  the  crowns,  a  yellow 
discoloration  being  sometimes  found  in  these  portions  of  the  natural 
teeth.  The  imitation  of  an  eroded  area  in  this  location  by  grinding 
the  surface  which  is  then  stained  yellow,  and  the  staining  of  the  occlu- 
sal surfaces  of  the  teeth  to  imitate  the  discoloration  of  the  dentine  ob- 
served in  the  mouth  of  users  of  tobacco,  are  the  ones  most  commonly  of 
service. 

The  imitation  of  the  discoloration  incident  to  devitalization  of  a 
tooth  may  be  some  times  justifiable,  but  rarely  except  in  those  cases  in 
which  a  similar  condition  was  known  to  exist. 

The  opaque  white  spots  on  the  surface  of  the  incisors,  indicative  of  an 
error  in  the  development  of  the  enamel,  is  also  a  condition  which  may  be 
reproduced.  The  indication  for  this,  however,  seldom  presents  itself, 
and  it  is  only  really  necessary  for  partial  dentures  in  which  an  artificial 
tooth  is  to  be  made  to  match  natural  teeth  exhibiting  this  condition. 

The  method  of  producing  these  stained  effects  is  that  recommended 
by  Dr.  George  H.  Wilson  and  described  in  a  paper  "  Artistic  Staining  of 
Artificial  Teeth,"  in  the  Ohio  Denial  Journal. 

TINTING    AND    STAINING    PORCELAIN    TEETH. 

Changes  may  be  made  in  the  color  or  shades  of  teeth,  or  de^'italized 
and  discolored  teeth  may  be  imitated,  by  the  system  demonstrated  by 
Dr.  George  Cunningham  at  the  Columbian  Dental  Congress,  which 
consisted  in  the  application  of  a  set  of  paste  colors  or  the  stains  pre- 
pared and  furnished  by  Poulson  of  Dresden  or  Ash  Sons  of  London.^ 

The  colors  usually  employed  in  china  painting  will  answer  ver>'  well 
for  the  purpose,  and  a  small  selection,  consisting  of  sepia,  ivory  black, 

iProm  paper  on  "Artistic  Staining  of  Artificial  Teeth,"  in  Ohio  Denial  Journal,  by  Dr.  George 
H.  Wilson. 


430  SELECTION,  ARRANGEMENT,   AND  ARTICULATION. 

rose  pompadour  (gum  color),  ivory  yellow,  brown  yellow,  celestial  blue, 
and  relief  white  will  be  sufficient  with  which  to  form  almost  any  shade 
required  in  the  imitations  of  the  usual  discolorations  of  the  teeth  as  met 
with  in  the  natural  orijans. 

The  implements  recjuired  for  the  mixin<j;  and  apijjication  of  the  tints 
are  a  plain  glass  slab,  on  \\hich  to  mix  the  colors  in  small  quantities;  a 
small  palette  knife;  a  small,  short-bristled  brush  for  stippling  or  spread- 
ing the  color,  such  as  can  readily  be  formed  by  cutting  off  the  bristles 
of  a  camel's  hair  or  sable  brush,  so  that  the  remainder  is  short,  stubby, 
and  square  at  its  end;  alcohol,  with  which  to  clean  the  teeth;  brushes; 
oil  of  cloves,  oil  of  lavender,  or  turpentine  to  thin  the  paints  to  proper 
consistence. 

The  grays,  yellows,  and  browns  are  the  tints  most  frequently  recjuired 
in  imitating  the  (iiscolorations  of  the  natural  teeth.  Ivory  black  is  of 
course  not  to  be  used  by  itself,  but  it  is  indispensable  as  a  means  of 
deepening  the  color  of  the  grays  and  browns. 

In  the  use  and  application  of  pigments  for  the  purpose  of  staining 
porcelain  teeth  the  operator  should  study  the  colors  of  the  natural 
organs  as  met  within  the  mouths  of  patients,  and  he  should  acquire 
experience  in  noting  the  eflFect  of  admixture  of  the  pigments  when 
applied  to  porcelain  teeth.  This  is  essential,  as  the  colors  when  de^'el- 
oped  by  exposure  to  high  temperatures  are  not  always  of  the  degree  and 
shade  expected.  A  few  experiments,  which  can  easily  be  made  u])on 
odd  teeth  by  means  of  the  Downie  or  Custer  furnace,  will  enable  the 
operator  to  apply  the  colors  with  some  degree  of  certainty. 

Imitations  of  gold  fillings  in  porcelain  teeth  are  admissible  only  when 
done  for  the  purpose  of  closely  imitating  conspicuous  natural  teeth,  thus 
protecting  the  patient  from  sudden  change  of  a])pearance.  The  tooth  or 
teeth  to  be  so  treated  are  to  be  first  fitted  accurately  to  place  and  care- 
fully articulated.  The  portion  of  the  tooth  to  receive  the  imitation 
filling  should  be  slightly  depressed  by  grinding  with  a  corundum  wheel, 
so  as  to  allow  for  the  reciuired  thickness  of  the  gold,  which  is  the  same  as 
is  usually  employed  by  china  decorators.  It  is  known  as  "  Roman 
gold,"  and  is  laid  on  with  a  camel's  hair  pencil.  I'sually  three  or  four 
layers  will  be  necessary  to  enable  the  gold  to  withstand  the  attrition 
to  which  it  will  be  subjected  in  the  mouth.  Each  layer  must  be  sepa- 
rately burned  in  the  furnace. 

The  occasions  requiring  tinting  or  staining  are  not  numerous,  and  the 
system  should  be  applied  with  taste  and  judgment.  These  occasions  are 
found  in  cases  where  it  is  necessary  to  imitate  the  discoloration  of  a 
devitalized  tooth;  to  deepen  the  color  of  the  cuspids;  to  imitate  the  dis- 
coloration of  the  dentine  left  bare  by  the  recession  of  the  gums;  to 
darken  the  dentine  between  the  plates  of  enamel  on  the  cutting  edges  of 
the  teeth  of  elderly  subjects;  to  imitate  the  opaque  or  white  spots  in  the 
enamel  of  incisors  or  cuspids,  or  the  yellow  spots  occasionally  seen  on  the 
surfaces  of  the  incisors. 

In  applying  the  stains  the  tooth  should  be  thoroughly  cleaned  with 
alcohol,  dried,  and  held  by  the  pins  with  a  pair  of  pliers:    the  color  is 


ARTICULATION  OF  THE  BICUSPID  AND  MOLAR   TEETH.     431 

mixed  with  oil  of  cloves  or  lavender  and  applied  with  a  camel's  hair 
pencil,  the  quantity-  or  thickness  being  governed  by  the  depth  of  shade 
required. 

The  color  is  fixed  by  subjecting  the  teeth  to  a  temperature  of  about 
2000°  F.  The  firing  may  be  satisfactorily  accomplished  in  either  of  the 
furnaces  above  named,  or,  as  described  by  Dr.  George  H.  Wilson,  "by 
shaping  a  piece  of  No.  36  platinum  plate  so  as  to  cover  and  enclose  the 
teeth,  except  on  one  side,  which  is  left  open  as  a  peep-hole.  This  minia- 
ture oven  or  furnace  containing  the  teeth  is  placed  over  the  Bunsen  burner 
for  about  five  minutes,  when  the  flame  from  the  blowpipe  is  placed 
against  the  outside  of  the  clay  slab,  upon  which  it  is  held,  and  gradually 
bringing  it  over  upon  the  top  of  the  platinum,"  two  minutes'  work  of 
the  blowpipe  being  sufficient,  to  vitrefy  and  fix  the  colors. 

"Atrophy  and  worn  conditions  are  imitated  by  grinding  and  then 
staining."  Gum  colors  are  formed  by  the  use  of  the  rose  pompadour, 
the  depth  of  the  shade  being  secured  by  varying  the  amount  of  the 
relief  white. 

THE  ARTICULATION  OF  THE  BISOUPID  AND  MOLAR  TEETH. 

When  all  is  said  about  the  purposes  of  artificial  dentures,  it  will  be 
seen  that  their  chief  function  is  the  repair  of  the  apparatus  by  which 
mastication  is  accomplished.  The  molar  and  bicuspid  teeth  are  para- 
mount factors  in  the  accomplishment  of  this  object.  Their  form  and 
arrangement  should  be  determined  almost  solely  by  considerations  rel- 
ative to  this  purpose.  They  also  contribute  by  their  arrangement  to 
the  general  object  of  plate  maintenance.  The  correct  placing  and  form 
to  be  given  them  to  promote  these  purposes  will  now  be  considered. 

A  knowledge  of  the  form  and  functional  relations  of  the  natural  teeth 
will  be  of  great  assistance  in  the  articulation  of  the  artificial  bicuspids 
and  molars.  While  it  is  not  possible  to  exactly  reproduce  in  the 
artificial  teeth  the  form  and  arrangement  of  the  natural,  because  of 
essential  differences  in  the  conditions  attending  their  use,  much  may 
be  learned  from  a  study  of  the  normal  operation  of  mastication  in  a 
typical  or  ideal  natural  denture.  As  placed  in  the  mouth,  the  natural 
teeth  are  firmly  imbedded  in  the  alveolar  process,  and  during  their  use 
for  purposes  of  mastication,  stress  may  be  applied  to  them  in  a  variet}- 
of  directions.  On  the  other  hand,  artificial  teeth  are  mounted  upon  a 
base  supported  upon  the  mucous  membrane,  and  they  must  be  so 
formed  and  located  that  not  only  is  the  stress  which  is  exerted  upon 
them  in  the  crushing  of  the  food  to  be  so  arranged  as  to  be  best  resisted 
by  the  tissues  supporting  the  plate,  but  that  stress  must  be  so  disposed 
as  to  hold  the  dentures  firmly  upon  their  base  instead  of  causing  them 
to  be  displaced.  These  essential  dift'erences,  therefore,  exist  between 
natural  and  artificial  dentures  and  the  principles  utilized  in  the  former 
must  be  modified  and  adapted  to  promote  the  best  interests  of  the 
latter. 

Two  objects  are,  therefore,  held  in  view  in  the  articulation  of  artificial 


432  SELECTION,  ARRAXGEMENT,  AND  ARTICULATION. 

teeth:  first,  to  have  the  teeth  shaped  and  located  so  that  they  may  he 
brono;ht  into  effective  functional  relations  durinf];  the  movement  of  the 
mandible;  second,  to  so  arranfjc  them  that  the  stress  brought  upon 
them  during  their  use  in  mastication  will  serve  to  maintain  the  dentures 
upon  their  support  and  not  to  displace  them.  How  may  this  be  ac- 
complished ? 

Let  us  first  direct  attention  to  several  characteristics  of  an  ideal 
natural  denture  which  have  to  do  with  the  function  of  mastication.  In 
the  natural  jaw  there  is  a  definite  relation  between  the  form  of  the 
occlusal  surfaces  of  the  teeth  and  the  path  which  the  condyle  pursues, 
and  in  consecpience,  with  the  movement  of  which  the  mandible  is  capable. 
It  has  been  shown  in  Chapter  IV.  how  this  relationship  renders  the  den- 
ture a  more  effective  masticating  apparatus.  This  principle  is  to  be 
applied  to  artificial  teeth;  for  while  it  is  rarely  the  case  that  in  a  natural 
denture  the  teeth  absolutely  follow  the  typical  design  for  the  apparatus. 

Fig.  397 


Diagram  showing  typical  proportion  between  cusp  length  overbite  and  compensating  curve. 

jVIodified   from   Bonwill. 

in  the  artificial  denture  the  forms  and  positions  of  the  teeth  are  under 
control  and  may  be  determined  and  co-ordinated  with  the  mandibular 
movements. 

In  the  natural  teeth  the  molar  and  bicuspid  series  presents  two  rows  of 
cusps,  the  outer  and  inner.  The  buccal  cusps  of  the  lower  and  the  lingual 
of  the  upper  are  received  into  f ossse  between  the  cusps  of  the  opposed 
series.  While  it  is  not  pos.sible  to  exactly  reproduce  in  the  artificial  teeth 
the  forms  of  the  individual  cusps  constituting  these  two  lines  or  the 
fossa?  into  which  they  are  received,  it  is  possible  to  represent  the  lines 
of  cusps  by  ridges  which  are  received  into  sulci,  and  for  all  practical 
purposes  the  masticatory  function  maybe  executed  by  teeth  thus  shaped. 

It  will  be  remembered  that  in  the  typical  natural  denture  the  so-called 
"compensating  curve"  of  the  bicuspid  and  molar  teeth  is  directly  cor- 
related with  the  path  pursued  by  the  condyle  in  its  forward  excursion. 


ARTICULATION  OF  THE  BICUSPID  AND  MOLAR   TEETH.      433 

(Fig.  397.)  This  provides  for  a  sliding  contact  between  the  two  series, 
upper  and  lower,  in  the  forward  movements  of  the  mandible  until  its 
anterior  end  is  depressed  by  the  sliding  of  the  lower  incisors  upon  the 
lingual  surface  of  the  upper.  The  compensating  curve  is  a  continua- 
tion of,  or  is  concentric  with,  the  path  pursued  by  the  condyle.  This 
correlation  is  to  be  established  by  the  form  and  arrangement  of  the  arti- 
ficial teeth  to  subserve  a  similar  end. 

It  will  also  be  remembered  that  the  buccal  cusps  of  both  upper  and 
lower  series  are  placed  at  a  progressively  higher  level  from  the  first 
bicuspid  to  the  last  molar.  Also  that  the  buccal  cusps  of  the  lower 
and  the  lingual  cusps  of  the  upper  are  the  larger  of  the  lines  of  cusps 
and  that  these  become  relatively  lars^er  from  before  backward.  This 
permits  a  sliding  contact  between  the  teeth  in  the  lateral  excursion  of 
the  jaw.  When  the  mandible  is  moved  to  the  right  side  for  instance, 
the  high  buccal  cusps  of  the  lower  series  on  the  right  side  slide  upon  and 
come  in  contact  with  the  short  buccal  cusps  of  the  upper,  the  large 
lingual  cusps  of  the  upper  being  at  this  time  in  contact  with  the  lingual 
cusps  of  the  lower  series.  (Fig.  398.)  On  the  side  opposite  to  that 
from  which  the  movement  has  taken  place,  the  high  buccal  cusps  of 
the  lower  have  moved  upon  the  large  lingual  cusps  of  the  upper,  the  de- 
scent of  the  condyle  on  this  side  making  it  necessary  that  two  long 
cusps  be  in  relation  to  preserve  the  contact.  When  the  mandible  is 
brought  back  to  the  position  of  the  resting  bite,  the  sliding  contact  is 
maintained.  A  correspondingly  similar  relation  of  the  teeth  exists  when 
it  is  carried  to  the  left  side.  This  characteristic  of  the  ideal  natural 
denture  is  also  to  be  reproduced  in  the  artificial. 

In  the  natural  denture,  when  the  mandible  is  protruded  in  incision 
to  bring  the  occlusal  edges  of  the  incisors  into  contact,  there  is  no  con- 
tact between  the  distal  teeth  of  the  two  series.  In  the  artificial  denture 
the  overbite  of  the  upper  incisors  is  to  be  made  less  than  its  natural  pro- 

FiG.  398 


Diagram  illustrating  contact  of  cusps  in  lateral  excursion  of  the  mandible.  Section  through 
jaws  at  position  of  second  molar.  O  P,  line  touching  lingual  cusps  of  upper  molars;  L  R,  line 
touching  buccal  cusps  of  upper  molars  ;  S  T,  line  touching  buccal  cusps  of  lower  molars,  showing 
the  downward  movement  of  the  mandible  on  the  right  side  necessary  for  contact  of  the  cusps. 

totype,  so  that  when  the  mandible  is  protruded  for  incision  and  the 
incisors  are  in  edge-to-edge  relation,  contact  between  the  last  molars 
of  the  series  is  to  exist  at  the  same  time.     It  will  be  seen  that  this  ar- 

28 


43-t  SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 

rangement  of  the  forms  and  positions  of  the  artificial  teeth  provides 
for  a  simultaneous  contact  between  the  series  of  the  two  sides  during 
the  lateral  movement  of  the  mandible  in  mastication.  This  serves  to 
maintain  both  upper  and  lower  plate  dentures  in  place  by  pressing  them 
firmly  upon  the  tissues  which  give  them  support.  During  the  use  of  arti- 
ficial dentures  for  mastication  this  provision  greatly  contributes  to  their 
maintenance.  It  does  not,  of  course,  provide  against  displacing  stresses 
occurring  in  mastication  before  the  two  series  have  come  into  contact, 
and  during  the  passage  of  the  cusps  through  the  food  until  those  of  the 
two  series  touch;  but  in  the  retraction  of  the  jaw  from  this  point  to 
the  position  of  the  resting  bite,  during  which  time  the  chief  crushing 
of  the  food  takes  place,  the  teeth  preserve  a  sliding  contact  which  tends 

Fig.   399 


Diagrammatic    view  of  the    relative  height  of  the   buccal  and  lingual   cusps  of  the  molar  and 

bicuspid  teeth.     (W'alker.) 

to  keep  the  dentures  in  place.  This  arrangement  of  the  teeth  also 
assists  in  the  maintenance  of  the  plates  during  the  operation  of  incision, 
for  as  soon  as  the  incisors  have  met  through  the  food  that  is  being 
incised,  the  distal  teeth  are  in  contact,  and  as  the  mandible  is  retracted 
to  the  position  of  occlusion,  the  lower  incisors  slide  upon  the  upper  and 
the  plates  are  firmly  pressed  into  place. 

We  shall  now^  discuss  considerations  pertaining  to  the  proper  placing 
and  correct  form  of  the  teeth  to  accomplish  these  ends.  The  bicuspids 
and  molars  obtained  from  the  manufacturers  are  illy  shaped,  as  a  rule, 
to  serve  the  ends  of  this  arrangement.  The  upper  molars  and  bicuspids, 
for  example,  have  longer  buccal  than  lingual  cusps  which  is  the  reverse 
of  that  observed  in  the  natural  teeth.  They  are  also,  as  a  rule,  too 
narrow  bucco-lingually.  Teeth  should  be  selected,  therefore,  which 
will  admit  of  considerable  alteration  in  their  form.  It  is  especially  im- 
portant to  have  a  sufficient  bulk  of  porcelain  occluso-gingivally,  so  that 
the  grinding  of  a  sulcus  between  the  buccal  and  lingual  cusps  will  not 
too  greatly  weaken  them.  They  should  also  be  as  wide  bucco-lingually 
as  possible.  The  alteration  in  form,  as  recommended  by  Dr.  Bon  will, 
may  be  best  done  with  corundum  stone  one  and  one-half  inches  in  di- 
ameter and  an  eighth  of  an  inch  wide,  with  a  round  edge.  It  is  purposed 
to  grind  them  so  that  the  buccal  and  lingual  cusps  shall  have  the  corre- 
sponding relative  size  and  height  characteristic  of  the  natural  teeth. 


ARTICULATION  OF  THE  BICUSPID  AND  MOLAR   TEETH.     435 

This  is  done  chiefly  by  deepening  the  sulcus  between  the  buccal  and 
lingual  cusps  and  altering  the  height  of  these  cusps.  Fig.  399  gives  a 
diagrammatic  profile  view  of  the  upper  and  lower  series  of  one  side. 
It  will  be  obse^^'ed  that  the  buccal  cusps  of  the  upper  are  smaller  and  are 
placed  at  a  p^og^essi^'ely  higher  level  from  before  backward.  This  latter 
characteristic  is  obtained  by  an  actual  decrease  in  the  height  of  the  cusps 
and  by  an  increasing  inclination  of  the  long  axes  of  the  teeth  from  the 
\'ertical.  In  the  lower  series  the  buccal  cusp  increases  in  size  and  is 
placed  at  a  progressively  higher  level,  as  illustrated  in  the  figure.  For 
the  upper  artificial  teeth,  therefore,  a  sulcus  should  be  ground  which 
approximates  nearer  to  the  buccal  side  of  the  teeth  as  one  goes  from  the 
first  bicuspid  to  the  second  molar.  The  buccal  cusps  must  be  shortened 
and  their  size  diminished.  The  lingual  cusp  is  to  be  rounded  and  pre- 
served as  high  as  possible. 

It  is  suggested  by  Walker^  that  the  second  molar  be  given  more  nearly 
the  form  of  the  third  natural  molar  by  having  a  pronounced  lingual 
cusp  and  a  very  small  buccal  cusp.  It  is  observed  in  the  natural  den- 
ture that  the  lingual  cusp  of  the  third  molar  is  chiefly  the  one  in  contact 
with  the  lower  teeth  in  the  movement  of  the  mandible.  In  the  artificial 
teeth  this  arrangement  will  promote  the  stability  of  the  denture  by  re- 
moving the  lingual  cusp  from  occlusal  contact,  audit  will  be  seen  that  as 
this  cusp  is  farthest  removed  from  the  line  of  the  alveolar  ridge,  plac- 
ing it  out  of  contact  with  the  lower  will  reduce  the  displacing  tendencies 
acting  upon  the  plate. 

In  cutting  the  lower  teeth  the  lingual  cusp  is  to  be  reduced  in  height, 
and  the  sulcus  dividing  the  two  lines  is  to  approach  the  lingual  surface 
of  the  series  more  closely  from  before  backward.  Bonwill  has  called 
attention  to  the  advisability  of  removing  the  lingual  cusp  from  the  first 
lower  bicuspid,  because  it  does  not  have  functional  relations  with 
the  upper  series  in  the  movement  of  the  jaw.  The  buccal  cusps  of 
the  lower  are  to  be  rounded  and  preserved  as  high  as  possible.  (Fig. 
400.) 

Recently,  several  manufacturers  have  placed  so-called  "anatomical 
molds"  upon  the  market  which  are  a  great  improvement  upon  the  teeth 
formerly  in  general  use.  These  new  molds  are  designed  to  give  the 
occlusal  surfaces  of  the  teeth  such  cusps  and  fossae  as  to  enable  one  to 
set  them  up  in  correct  occlusion  with  the  same  interdigitation  of  the 
cusps  as  obtains  in  natural  dentures.  Many  of  these  molds  give  ex- 
cellent occlusal  relations  of  the  cusps  and  in  some  instances  they  may 
be  made  to  articulate  in  the  side  and  forward  movements  of  the  articula- 
tor in  a  very  satisfactory  manner,  although  some  slight  alteration  of  a 
cusp  here  or  there  is  usually  necessary  with  even  the  forms  of  best  de- 
sign. It  is  hoped  and  believed  that  before  many  years  forms  will  be 
obtainable  which  will  require  little  or  no  alteration  for  use  in  the  average 
case. 

1  The  Dental  Cosmos,  vol.  xxxviii.,  p.  41. 


48(5 


SELECTION,   ARRANGEMENT,   AM)  ARTICI'LATfON. 


THE  TECHNIQUE  OF  THE  SETTING  OF    THE  BICUSPID  AND 
MOLAR  TEETH. 

The  six  upper  anterior  teeth  having  been  correctly  placed,  as  alread} 
described,  the  placing  of  the  molar  and  bicuspid  teeth  upon  the  casts  is 
then  undertaken.  Bearing  in  mind  the  relationship  between  the 
cusp  length,  the  overbite,  the  compensating  curve,  and  the  path  of 
the  condyle,  it  will  be  seen  that  these  must  be  in  accord  in  each  individ- 
ual denture.  If  the  casts,  therefore,  have  been  correctly  placed  upon  an 
articulator  capable  of  individualizing  the  movements  of  the  mandible,  and 

Fig.  400 


Series  of  artificial  fjicuspid  and  molar  teeth  cut  for  articulation. 

the  paths  of  the  condyles  have  been  recorded,  and  the  articulator  adjusted 
to  reproduce  thern,  then  the  teeth  must  be  arranged  so  that  the  cusp 
length,  overbite  and  compensating  curve  factors  are  in  accord  there- 
with. As  the  overbite  may  be  arranged  to  accord  with  the  cusp  length  and 
the  compensating  curve  after  they  have  been  established,  these  two 
factors  must  be  harmonized  with  the  condylar  path.  It  will  be  re- 
membered that  long  cusps  are  associated  with  a  marked  downward  in- 
clination of  the  path  of  the  condyle,  and  that  short  cusps  are  found  in 
cases  in  which  the  path  is  not  much  inclined.  It  will  also  be  remem- 
bered that  long  cusps  are  associated  with  a  compensating  curve  of 
short  radius,  and  short  cusps  with  a  curve  of  long  radius.  If,  therefore, 
the  length  of  the  cusps  is  decided  upon  for  a  particular  case  to  accord 
with  the  path  of  the  condyle,  only  one  of  the  fixed  factors  in  this  joint 
relationship,  the  compensating  curve,  remains  to  be  determined,  and 
this  curve  may  be  made  to  accord  with  the  cusp  length  and  the  con- 
dylar path. 

The  lengths  of  the  cusps  of  the  individual  teeth  have  a  direct  pro- 
portion to  each  other,  so  that  the  cusps  of  one  tooth  of  the  series  having 
been  determined,  the  others  may  be  made  to  accord  therewith.  These 
facts  make  it  evident  that  if  in  the  process  of  setting  the  teeth,  the 
length  of  the  cusps  of  the  bicuspids  is  determined,  then  the  other  re- 
lated factors  may  be  made  harmonious  therewith. 

The  length  of  the  cusps  on  each  side  is  to  be  determined  in  part  by 
the  temperamental  indication  of  the  patient,  but  chiefly  by  reference 


TECHNIQUE  OF  SETTING    THE   TEETH.  437 

to  the  path  of  thf  coiulyle  in  luronhuice  with  the  ijriiuijjk-s  ahove  out-* 
lined.  These  teeth  should  be  cut,  therefore,  and  phiced  in  their  proper 
position  upon  the  upper  cast  in  rehition  with  the  lower  l)ite-plate.  It 
will  be  remembered  that  the  compensatiiifj  curve  begins  at  this  point, 
and  they  should  be  placed  tentatively  in  line  with  the  upper  teeth 
already  in  position  and  in  correct  relation  w  ith  them,  carefully  preserving 
the  distance  between  the  casts  by  means  of  the  calipers  already  re- 
ferred to.  The  lower  bite-plate  is  removed,  and  the  second  lower  bi- 
cuspid cut  to  accord  with  the  height  of  the  cusps  of  the  upper  teeth,  is 
then  placed  to  correctly  articulate  with  them.     (Fig.  401.)  The  buccal 

Fig.   401 


Casts  on  articulator  with  ten  upper  anterior  teeth  and  second  lower  bicuspids  in  place. 


and  lingual  cusps  of  the  first  upper  bicuspid  should  be  in  the  same 
horizontal  plane,  and  the  teeth  given  correct  positons  so  far  as 
the  direction  of  their  long  axes  is  concerned.  This,  it  will  be  seen 
fixes  the  path  of  movement  of  the  lower  bow  of  the  articulator,  repre- 
senting the  lower  jaw^,  while  the  teeth  are  in  contact.  The  lower  cast 
may  be  moved  in  relation  to  the  upper  only  along  fixed  paths  so  long  as 
the  sliding  contact  is  preserved,  and  the  teeth,  which  are  subsequently 
placed  in  position,  may  be  made  to  come  into  contact  in  correct  func- 
tional positions. 

The  first  molar  teeth  of  the  low^er  jaw  are  then  to  be  placed  in  posi- 
tion. They  are  cut  with  cusps  of  size  relative  to  the  lower  bicuspids 
already  in  place,  and  are  to  have  their  distal  cusps  elevated  in  accord 
with  the  prospective  compensating  curve.  Their  buccal  cusps  should 
also  be  slightly  higher  than  their  lingual.  The  lower  bow  of  the  ar- 
ticulator should  now  be  moved  to  one  side,  and  it  should  be  observed 
if  the  contact  between  the  bicuspids  is  interrupted  because  of  contact 
with  the  molar,  or  whether  the  contact  of  its  cusps  with  the  second 
upper  bicuspid  accords  w^ith  that  of  the  other  teeth.     If  it  does  not,  it 


438  SELECTION,   ARRANGEMENT,  AND  ARTICULATION. 

should  be  so  altered  in  cusp  length  or  position  or  inclination  as  to  make 
it  in  contact  with  the  second  upper  bicuspid  durinj;  these  movements. 
The  first  upper  molar  on  each  side  is  then  to  be  placed  in  position  in 
proper  occlusal  relation  with  the  first  lower.  The  lower  bow  of  the  artic- 
ulator is  again  to  be  moved  laterally;  the  sliding  contact  of  the  upper 
molar  is  to  be  tested  in  a  manner  similiar  to  that  of  the  lower,  and  anv 
alteration  in  its  position  or  cus.p  length  made  to  insure  its  continued 
contact  during  these  movements. 

Fig.   402 


Casts  with  all  bicuspids  and  molars  in  place.     Side  view. 

Enough  of  the  teeth  have  been  placed  in  position  now  to  take  cog- 
nizance of  the  compensating  curve,  and  the  lower  bow  of  the  articulator 
should  be  carried  forward  to  test  this.  In  this  movement  the  lingual 
cusps  of  the  upper  should  slide  in  the  sulci  of  the  lower  and  slightly 
upon  the  buccal  cusps  of  the  lower.  The  more  divergent  are  the  lines  of 
the  teeth  from  the  canines  backward,  the  more  will  the  upper  lingual 
cusps  mount  the  lower  buccal,  and  the  more  nearly  parallel  are  these 
lines  of  teeth,  the  more  will  these  cusps  slide  in  the  grooves.  If  the 
compensating  curve  is  not  sufficiently  great,  the  contact  of  the  molars 
will  be  interrupted  by  this  movement.  It  is  evident,  therefore,  that  the 
cusps  of  the  upper  and  lower  molars  are  placed  below  the  proper  com- 
pensating curve  and  the  curve  must  be  increased  by  inclining  the  long 
axes  of  the  molar  teeth  a  little  farther  forv/ard,  and  then  raising  them  to 
the  necessary  position  of  the  compensating  curve.  On  the  other  hand,  if 
in  this  movement  it  is  the  bicuspids  which  are  separated,  it  is  evident 
that  the  compensating  curve  is  made  too  great,  and  the  line  of  contact 
between  the  upper  and  lower  molars  is  above  their  desired  position 
in  the  proper  compensating  curve.  Any  necessary  alterations  in  their 
positions  to  make  them  accord  with  this  arrangement  must  then  be 
made. 


TECHNIQUE  OF  SETTING   THE  TEETH.  439 

The  second  lower  molars  are  then  to  be  placed  in  position,  having 
been  cut  to  tentative  form.  The  lateral  movements  of  the  articulator 
are  produced  as  before,  and  the  contact  of  their  cusps  with  those  of 
the  first  upper  molar  tested  in  a  similiar  way.  Alterations  in  their  form 
or  position  will  be  indicated  to  make  them  accord  with  the  preservation 
of  an  uninterrupted  contact  with  the  upper  teeth  in  these  movements. 
It  is  particularly  important  to  remember  their  natural  lingual  inclination 
and  the  increased  height  of  their  buccal  cusps.  In  the  forward  move- 
ment of  the  lower  bow  of  the  articulator  their  conformation  to  the  de- 


FlG.    403 


Lower  bow  of  articulator  carried  to  one  side  to  show  contact  of  molars. 

sired  compensating  curve  is  tested,  and  they  should  be  located  in  ac- 
cordance with  the  indications. 

The  second  upper  molar  is  then  to  be  placed  in  position  and  its  form 
altered  or  its  position  changed  as  the  movements  of  the  lower  bow  of  the 
articulator  indicates  to  be  necessary.    (Fig.  402.) 

In  the  making  of  these  adjustments  between  the  teeth,  it  is  first 
desirable  to  bear  in  mind  their  general  relation  to  the  compensating 
curve.  It  is  also  desirable  to  place  the  molar  teeth  as  nearly  over  the 
alveolar  ridges  as  possible,  and,  except  in  cases  of  extreme  absorption 
of  the  process,  this  may  be  measurably  accomplished. 

Inasmuch  as  the  line  of  force  upon  the  two  dentures  should  as  nearly 
as  possible  coincide  with  an  imaginary  line  drawn  from  one  ridge  to 
the  other,  the  long  axes  of  the  artificial  teeth  should  be  as  far  as  is  ex- 
pedient placed  in  this  imaginary  Hne.  (Fig.  404.)  The  outward  inclin- 
ation of  the  upper  teeth  and  the  Kngual  inclination  of  the  lower  will 
make  this  possible,  and  not  conflict  with  the  other  requirements  in  the 
position  of  these  teeth.     In  general,  it  may  also  be  said  that  the  line 


440 


SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 


of  the  occlusal  surfaces  of  these  teeth  should  he  ahout  midway  between 
the  upi)er  and  lower  ahcolar  ridjics,  although  differences  in  resori)tion 
in  the  two  jaws  or  in  the  two  sides  of  the  same  jaw  may  make  slight 
alteration  in  this. 

The  first  lower  bicuspid  is  now  to  be  placed  in  position  in  correct 
functional  relations  with  the  upper  canine  and  first  bicuspid.  The 
lower  bow  of  the  articulator  should  be  moved  l)oth  laterally  and  for- 
ward to  test  the  contact  of  this  tooth  in  these  various  relations. 

Only  the  six  lower  anterior  teeth  now  remain  to  be  placed  in  position. 
It  is  desirable  that  they  should  fulfil  both  functional  requirements  and 

Fia.  404 


DiaKrain  showing  section  through  mouth  with  molars  in  occlusion  and  line  drawn  between  edges 
corresi)onding  to  the  long  axes  of  the  teeth. 

those  imposed  by  considerations  of  appearance.  Their  position  rel- 
ative to  each  other  to  fulfil  the  demands  of  appearance  have  already 
been  considered.  To  subserve  the  ends  of  function,  they  are  to  be 
placed  in  position  so  that  when  the  lower  bow  of  the  articulator  is  pro- 
truded, they  are  in  occlusal  contact  with  the  upper  teeth.  Where  condi- 
tions of  wear  are  to  be  simulated,  they  must  first  be  ground  for  this 
purpose  and  then  placed  in  such  position  that  when  the  lower  bow 
of  the  articulator  is  moved  forward,  their  occlusal  ends  touch  those  of 
the  upper  teeth.  They  must  also  be  arranged  so  that  in  the  lateral  move- 
ment of  the  jaw  they  do  not  strike  the  upper  teeth  and  thus  displace  the 
dentures. 

In  summing  up  the  characteristics  of  artificial  teeth  arranged  accord- 
ing to  this  plan,  it  will  be  seen  that  they  differ  from  the  natural  teeth  in 
the  following  particulars:  the  cusps  are  lower  than  their  natural  pro- 
totypes, and  this  is  because  by  this  means  the  stable  retention  of  the 
plate  is  best  promoted.  The  higher  the  cusps  are,  the  greater  leverage 
there  is  upon  the  dentures.  It  may  be  asked  why  the  sliding  contact 
between  the  dentures  might  not  be  preserved  and  the  maintenance 
of  the  plate  best  secured  by  having  the  teeth  with  fiat  surfaces  instead 
of  with  cusps.     Of  this  it  may  be  said  that  the  advantage  of  the  cusp 


TECHNIQUE  OF  SETTTNO   THE  TEETH.  441 

and  fossa  principle  in  the  mastication  of  food  has  already  been  outlined 
in  Chapter  IV.  Furthermore,  clinical  experience  has  shown  that  arti- 
ficial dentures  mounted  with  teeth  whose  cusps  have  been  ground  are 
by  no  means  as  effective  for  their  wearers  in  the  preparation  of  food, 
as  those  in  which  the  cusps  exist.  G.  V.  Black  has  also  shown  the 
greater  efficiency  of  a  cusped  crusher  in  the  preparation  of  various 
articles  of  food.  His  experiments  with  the  phago-dynamometer  show 
that  whereas  the  average  force  which  may  be  exerted  with  the  natural 
bicuspid  and  molar  teeth  is  over  150  to  175  pounds,  the  average  possible 
with  artificial  dentures  is  only  from  20  to  30  pounds.  He  has  also 
shown  that  this  latter  is  not  sufficient  in  many  instances  to  crush  some 
of  the  more  resistent  articles  of  food,  while  Head  has  demonstrated 
the  greater  masticating  efficiency  of  the  triturating  motion  which,  of 
course,  is  best  obtained  in  artifical  dentures  articulated  according  to 
the  plan  above  outlined. 

Because  of  the  flattening  of  the  floor  of  the  glenoid  fossa  in  edentulous 
cases,  as  mentioned  in  Chapter  IV.,  it  will  be  seen  that  the  path  of  the 
condyle  is  not  so  inclined  as  that  existing  earlier  in  life,  when  the  nat- 
ural teeth  are  in  position.  Inconsequence,  the  compensating  curve  for 
artifical  teeth  will  be  of  longer  radius  than  that  commonly  formed  by 
natural  dentures.  It  has  also  been  shown  that  for  purposes  of  stability 
of  the  plate,  the  natural  overbite  is  to  be  lessened. 

Because  of  the  resorption  of  the  alveolar  ridge,  the  teeth  of  any  ar- 
tificial set  must  be  slightly  smaller  than  the  natural  teeth  which  pre- 
ceded them.  This  fact,  together  with  the  necessity  already  mentioned 
for  placing  them  as  nearly  as  possible  over  the  ridge,  will  make  the  posi- 
tion of  their  long  axes  slightly  different  from  that  of  the  natural  teeth. 

To  Dr.  E.  S.  Ulsaver  is  due  the  credit  of  working  out  the  following 
method,  quoted  by  Clapp,^  of  determining  the  tooth  curves  in  the  bite- 
plates  after  which  the  upper  teeth  may  be  set  up  upon  the  lower  bite- 
plate,  and  the  lower  in  turn  articulated  with  the  upper : 

"Upon  the  occlusal  surface  of  the  lower  trial  plate,  which  was  made 
flat  and  has  not  been  changed,  is  dusted  a  white  powder,  such  as  soap- 
stone  or  talcum,  with  sufficient  evenness  so  that  any  scratches  upon  that 
surface  will  show.  The  trial  plates  are  then  closed  together  and  gentle 
pressure  is  made  from  the  most  anterior  portion  of  the  upper  model 
to  the  most  anterior  portion  of  the  lower  model  by  means  of  the  thumb 
and  finger.  By  pressure  on  the.  anterior  end  of  either  condyle  slot  the 
upper  model  is  moved  laterally  back  and  forth  several  times.  When 
the  trial  plates  are  separated  it  will  be  seen  that  the  occlusal  margin  of 
the  upper  trial  plate,  on  one  side,  has  rubbed  the  powder  noticeably  in 
several  spots.  If  both  occlusal  surfaces  are  smooth  and  level,  this  rub- 
bing will  probably  occur  first  in  the  bicuspid  region. 

"The  wax  of  the  lower  trial  plate  is  now  scraped  where  the  powder 
was  rubbed.  For  this  some  workers  prefer  an  old  blade  from  a  safety 
razor,  and  some  prefer  a  wooden  handled  ink  eraser,  such  as  is  common 
in  business  offices.    When  the  wax  in  the  rubbed  area  has  been  hol- 

'  "  The  Mechanical  Side  of  Anatomical  Articulation,"  by  George  W.  Clapp,  p.  72. 


442  SELECTION,  ARRANGEMENT,   AND  ARTICULATION. 

lowed  somewhat,  fresh  powder  should  be  dusted  on  and  the  rubbing 
and  scrapint;  process  repeated.  When  the  necessary  teclniic  has  been 
acquired,  the  scraping  or  carving  can  be  done  rapidly,  since  the  indica- 
tions of  the  first  rubbing  will  prove  a  reasonably  accurate  guide  for 
extensive  carving.  But  it  cannot  be  urged  too  strongly  upon  dentists 
who  care  to  anatomicall\-  articulate  dentures,  that  in  the  first  two  or 
three  sets  of  trial  plates  there  should  be  given  to  this  carving  enough 
time  and  attention  to  demonstrate  the  principles  and  methods  involved. 
The  time  spent  in  doing  this  will  bring  ample  rewards  in  the  future. 
Trial-plate  making  will  never  again  offer  difficulties. 

"This  form  of  carving  should  be  continued  on  one  side  only  until 
the  upper  trial  plate  rubs  the  powdered  surface  of  the  lower  to  the 
outer  margin  on  that  side.  The  other  side  may  then  be  carved  in  like 
manner.  This  is  as  far  as  this  form  of  carving  should  be  carried,  since 
it  is  not  desired  to  lower  the  labial  margin  of  the  lower  trial  plate.  If 
the  trial  plates  be  now  closed  together  and  examined  from  the  lingual, 
it  will  be  seen  that  while  the  outer  margin  of  the  lower  trial  plate 
remains  undisturbed,  the  occlusal  surface  has  been  considerably  in- 
clined toward  the  lingual.  This  inclination  will  be  lea.st  in  the  molar 
region  and  greatest  at  the  median  line. 

"  If  the  upper  model  be  moved  to  the  right  the  trial  plates  will  now 
remain  in  contact  on  the  left  side,  but  separate  noticeably  in  the  molar 
region  on  the  right.  The  amount  of  separation  will  depend  almost 
wholly  on  the  inclination  of  the  condyle  slots.  If  this  inclination  be 
very  slight,  say  only  10  degrees,  separation  between  the  heels  will 
be  slight.  If,  however,  the  inclination  of  the  condyle  slots  be  33  degrees, 
which  Gysi  thinks  is  the  average,  the  separation  will  be  noticeable. 
If  the  inclination  of  the  condyle  slots  should  be  60  or  70  degrees,  as 
is  found  in  some  cases,  the  separation  will  be  very  marked. 

"The  next  task  is  to  so  continue  the  curves  in  the  occlusal  surfaces 
of  both  trial  plates  that  this  separation  in  the  lateral  movement  may 
be  overcome.  This  may  be  done  by  building  up  the  heel  of  the  lower 
trial  plate  into  the  compensating  curve  and  then  carving  the  heel  of 
the  upper  trial  plate  to  fit  the  lower  as  thus  built. 

"The  heel  of  the  lower  trial  plate  is  built  up  as  follows:  Cut  across 
one  end  of  a  sheet  of  base  plate  wax  as  it  comes  in  the  box,  making  a 
strip  of  about  three-fourths  of  an  inch  wide.  Soften  this  on  one  side 
and  fold,  and  repeat  the  softening  and  folding  until  a  roll  has  been 
made  which  is  soft  all  the  way  through.  With  gentle  heat,  soften  one 
heel  of  the  lower  trial  plate,  place  the  little  roll  thus  made  on  the  heel, 
and  attach  it  firmly  by  means  of  a  hot  spatula  thrust  through  the 
roll  and  into  the  wax.  When  the  union  is  sufficiently  firm  for  working 
purposes,  moisten  with  water  the  occlusal  surface  of  the  upper  trial 
plate  directly  over  the  roll.  Before  bringing  the  trial  plate  together, 
move  the  upper  model  about  one-eighth  of  an  inch  toward  the  side  on 
which  the  roll  is  attached.  With  the  upper  thus  moved  laterally,  press 
the  models  together  until  the  trial  plates  come  in  contact  on  the  one  side 
opposite  to  the  roll.     (Fig.  405.)     Separate  the  trial  plates  and  trim 


TECHNIQUE  OF  SETTING   THE  TEETH. 


443 


away  the  excess  of  wax  to  the  hngual  and  buccal.  It  will  be  observed 
that  the  upper  ridge  did  not  flatten  the  roll  horizontally,  but  that  this 
surface  sho^^■s  an  inclination  upward  and  backward  from  the  occlusal 
surface  of  the  lower  trial  plate.  This  is  the  beginning  of  the  compensat- 
ing curve.  This  surface  also  slopes  lingually;  that  is,  the  elevation  is 
less  at  the  lingual  margin  than  at  the  buccal  margin.  This  is  the  begin- 
ning of  the  lateral  curve  in  this  section. 

"It  has  been  suggested  that  the  upper  model  be  moved  laterally 
only  about  one-eighth  of  an  inch,  because  it  is  found  that  if  the  model 
be  pulled  farther,  the  compensating  and  lateral  curves  are  exaggerated. 
So  far  as  we  are  able  to  determine  at  present,  practically  all  the  benefits 

Fig.  405 


Upper  models  moved  laterally  and  pressed  down  on  roll  on  heel  of  lower  bite.    (Clapp.) 


that  would  be  possible  from  even  the  most  exaggerated  curve  are 
secured  by  the  curve  that  results  from  moving  the  upper  model  one- 
eighth  of  an  inch.  Dentists  who  wish  to  carry  their  education  out  in 
this  matter  will  find  it  profitable  to  make  a  set  of  trial  plates  and  in 
carving  move  the  upper  model  as  far  laterally  as  the  articulator  permits. 
This  will  give  an  understanding  of  the  compensating  and  lateral  curves 
which  will  be  impossible  of  attainment  by  any  other  means. 

"  When  the  upper  model  is  allowed  to  return  to  a  position  of  central 
occlusion ,  the  trial  plates  will  be  kept  apart  by  the  built-up  heel  of  the 
lower.  (Fig.  406.)  At  the  point  of  contact  with  the  lower,  the  upper 
must  be  carved  to  permit  the  trial  plates  to  come  together  all  around. 
Begin  scraping  at  the  buccal-occlusal  margin  in  the  cuspid  region, 
scraping  harder  as  the  heel  is  approached.    The  scraped  surface  of  the 


444 


SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 


u\)\)vv  should  Iia\('  just  the  same  u|)\\ar(l  and  hackward  iuchuation  as 
tho  built-up  heel  of  the  lower,  it  should  have  just  the  same  lateral 
eurve,  so  that  in  the  position  of  eentral  oeelusion  the  built-up  surfaee 
of  the  lower  and  the  seraped  surface  of  the  upper  show  nearly  exact 
contact. 

"The  heel  of  the  upper  should  be  scraped  in  a  curve  somew^hat  longer 
than  that  shown  by  the  built-ui)  wax  on  the  lower  trial  plate.  That 
probably  extended  forward  only  to  the  bicuspids.  It  terminated 
abruptly,  leaving  a  sort  of  'jumping-oflf  place.'  The  curve  of  the 
upper  necessary  to  fit  the  built-up  lower  may  be  carried  forward  to  the 
location  of  the  cuspid.  When  the  trial  plates  are  in  contact  all  around, 
this  will  leave  a  triangular  open  space  anterior  to  the  flattened  roll. 


Fig. 406 


Bites  in  central  occlusion,  kept  apart  by  built-up  heel  of  lower.    (Clapp.) 


This  should  be  built  in  with  soft  wax  and  the  upper  trial  plate  moist- 
ened and  closed  down  on  it.  This  will  shape  it  to  conform  to  the  curve 
in  the  upper. 

"If,  by  pressure  on  the  same  condyle  slot  as  before,  the  upper  model 
be  now  moved  laterally,  a  slight  separation  will  probably  occur  between 
the  heels  of  the  upper  and  lower  trial  plates.  This  is  due  to  the  fact  that 
the  upward  curve  of  the  lower  trial  plate  was  shaped  by  the  occlusal 
surface  of  the  untrimmed  upper.  The  upper  now  having  been  trimmed, 
its  occlusal  surface  occupies  a  somewhat  difl^^erent  position,  hence  the 
separation.  Another  roll  of  wax  is  attached  to  the  occlusal  surface  of 
the  lower  trial  plate  in  the  same  place  and  in  the  same  way  as  the  first. 
The  occlusal  surface  of  the  upper  is  moistened  and  the  upper  model 


TECHNiqUE   OF  SETTING   THE   TEETH. 


445 


is  again  moN'ed  slightly  toward  that  side  and  pressed  down  until  the 
trial  plates  come  in  contact,  on  the  opposite  side.  This  will  be  found  to 
again  increase  the  height  of  the  heel  of  the  lower  on  that  side  and  to 
increase  also  the  compensating  and  lateral  curves.  The  upper  trial 
plate  is  again  carved  on  that  side  until  proper  relations  are  established. 
It  may  now  be  found  that  when  the  upper  model  is  moved  laterally 
through  the  one-eighth  of  an  inch  of  distance,  the  heels  of  the  two 
trial  plates  will  not  separate.  Should  a  separation  of  any  size  occur, 
it  may  be  remedied  by  a  third  building  in  like  fashion.  By  this  means, 
the  compensating  and  lateral  curves  may  be  so  accurately  worked  out 
that  no  separation  is  perceptible  between  the  trial  plates  through  the 
range  of  movement  mentioned.    The  trimming  of  the  wax  ma\'  usually 


Fig.  407 


The  corupcii^atnii;  and  lateral  curv 


rkcd  out  that  llu'  trial  j.latcs  do  n,.t  soparate.   (Clapp.) 


be  accomplished  in  much  less  time  than  is  here  required  to  describe  it, 
and  with  a  little  practice  the  whole  operation  becomes  very  rapid. 

"jMeantime,  the  opposite  sides  of  the  trial  plates  have  remained 
untouched.  Both  sides  should  not  be  put  in  work  at  the  same  time. 
That  is,  if  the  left  side  is  begun,  it  should  be  finished  before  the  right 
side  is  touched.  If  this  is  not  done,  but  both  sides  are  put  in  work  at  the 
same  time,  the  accuracy  secured  by  the  several  mechanical  steps  here 
outlined  will  be  lost.  The  carving  will  become  merely  time-consuming 
and  vexatious  guesswork." 

Dr.  George  H.  Wilson^  secures  a  balancing  of  the  dentures  by  simul- 
taneous contact  of  the  two  sides  by  a  method  slightly  different  from 
any  described  so  far.     He  says: 

1 "  Dental  Prosthetics,"  p.  240. 


446 


SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 


"Fig.  408  shows  the  twelve  upper  and  twelve  lower  teeth  mounted 
to  a  straight  horizontal  plane.  Should  any  of  the  teeth  be  loose  in  their 
setting,  they  are  made  fast  by  remelting  the  wax  about  them  with  an 
ironing  spatula,  and  the  wax  about  all  of  the  teeth  thoroughly  chilled 
for  the  next  step  of  setting  the  lower  second  molar. 


Fig.  408 


"A  portion  of  the  hardened  wax  just  back  of  the  lower  first  molar  is 
removed  and  a  ball  of  softened  wax  set  in  its  place.  The  occlusal 
surface  of  the  second  molar  is  ground  into  the  same  form  as  that  of  the 
first  molar,  and  set  upon  the  softened  ball  of  wax.  The  plane  of  the 
occlusal  surface  of  the  second  molar  should  be  nearly  parallel  with  the 


Fig.  409 


plane  of  the  condyle  path,  and  the  tooth  should  be  so  placed  that  the 
disto-occlusal  margin  of  the  upper  first  molar  will  glide  upon  the 
bucco-sulcus  plane  of  the  lower  second  molar  when  the  teeth  are  placed 
in  lateral  occlusion.  Fig.  409  shows  the  teeth  in  lateral  occlusion  and 
the  disto-occlusal  margin  of  the  upper  first  molar  in  contact  with  the 


TECHNIQUE  OF  SETTING   THE  TEETH.  447 

lower  second  molar.  It  is  obvious  that  if  all  the  teeth  but  the  lower 
second  molar  are  set  in  hardened  wax,  and  it  in  softened  wax,  working 
the  condyle  joint  forward  and  backward  repeatedly  will  aid  in  properly 
adjusting  the  second  molar.  Correctly  placing  the  three  molars,  the 
upper  first  and  the  lower  first  and  second,  is  the  key  to  the  mechanico- 
anatomical  antagonization;  and  the  secret  of  success  in  the  adjustment 
of  these  molars  is  in  keeping  the  disto-occlusal  margins  of  the  first 
molars  down.  They  may  be  depressed  a  trifle  below  the  plane,  but 
never  elevated  above  the  plane.  Herein  is  the  distinction  between  the 
mechanico-anatomical  arrangement  of  artificial  teeth  and  the  variously 
advocated  'anatomical'  arrangement  of  them.  By  observing  Figs. 
192  and  202  it  will  be  seen  that  the  anatomical  arrangement  of  natural 
upper  teeth  is  that  the  occlusal  surfaces  of  all  the  teeth,  from  the  central 
incisors  to  and  including  the  disto-buccal  cusp  of  the  first  molars,  are  in 
a  straight  horizontal  plane,  and  that  the  second  and  third  molars  are 
not  tilted,  but  stepped  upward.  So  far  as  the  author  knows  no  advocate 
of  the  so-called  'anatomical  articulation'  has  ever  suggested  repro- 
ducing this  upward  stepping  of  the  second  and  third  molars.  Hence, 
there  never  has  been  a  system  of  anatomical  arrangement  for  artificial 
teeth,  for  they  have  all  been  adaptations,  and  all  to  a  greater  or  less 
extent  have  opposed  a  physical  law.  The  physical  law  is  that  'force 
moves  at  right  angles  to  the  surface  from  which  it  emanates.'  There- 
fore, it  is  evident  that  the  system  that  least  opposes  this  physical  law 
is  superior  in  at  least  this  one  respect.  It  is  e\'ident  that  if  the  molars 
are  tilted  upward  at  any  angle  (the  greater  the  angle  the  greater  the 
leverage),  the  closing  movement  of  the  mandible  must  force  the  upper 
denture  forward,  and  that  if  it  were  not  for  the  interlocking  of  the  bicus- 
pids the  denture  could  not  be  retained  in  its  place.  As  the  first  molars 
must  assume  the  burden  of  crushing  hard  food,  it  is  logical  to  reason 
that  their  occlusal  surfaces  should  be  parallel  to  their  alveolar  base  of 
support.  If  the  crushing  of  food  were  the  only  function  of  artificial  den- 
tures, then  the  second  molars  should  be  placed  in  the  straight  occlusal 
plane;  however,  it  is  important  to  grind  the  food,  and  to  have  the  den- 
tures so  constructed  that  they  are  balanced  in  any  position  in  which  they 
may  be  occluded.  To  obtain  this  balanced  relationship  of  artificial 
dentures  it  is  necessary  to  have  more  or  less  of  the  teeth  placed  in  har- 
mony ^dth  the  condyle  path ;  but  to  secure  the  greatest  effectiveness  in 
crushing  and  grinding  the  food,  it  is  necessary  to  have  as  few  teeth  out 
of  the  horizontal  occlusal  plane  as  possible,  hence,  the  short  balancing 
curve,  or  'compensating  curve.'  This  term  'short  balancing  or 
compensating  curve'  is  in  contradistinction  to  the  long  'compensating 
curve,'  as  first  taught  by  Dr.  Bonwill. 

"Ha^^ng  developed  the  philosophy  of  this  particular  arrangement  of 
these  three  molars,  a  return  may  be  made  to  the  technique. 

"  In  like  manner  the  three  molars  are  adjusted  on  the  other  side  of  the 
case." 


448  SELECTKjy,  ARRANGEMENT,  AND  ARTICULATION 

TRIAL  OF  THE  DENTURES. 

Upon  theoretical  grounds  after  a  set  of  artificial  teeth  has  been 
articulated  so  as  to  have  correct  functional  relations  in  the  various 
movements  of  the  lower  bow  of  the  articulator,  they  should  be  capable 
of  correct  functional  relations  in  the  mouth.  The  fact,  however, that 
there  is  no  articulator  in  existence  or  probably  ever  will  be,  which  can 
absolutely  perfectly  reproduce  the  movements  of  the  mandible  in  a 
given  case,  makes  it  advisable  that  after  the  dentures  have  been  setup, 
their  functional  relations  should  be  tested  by  actual  trial  in  the  mouth. 
This  procedure  is  also  desirable  because  of  cosmetic  considerations. 
After  the  teeth  have  been  temporarily  mounted, therefore, they  should 
be  tried  in  the  mouth  of  the  patient. 

The  presence  of  the  patient  will  probably,  even  under  the  best 
circumstances,  provide  additional  data  in  the  matter  of  the  arrange- 
ment of  the  artificial  teeth.  In  many  cases  no  alteration  of  the  orig- 
inal arrangement  of  the  teeth  will  be  necessary,  but  this  depends  almost 
solely  upon  the  accuracy  with  w^hich  the  conditions  related  to  the  ar- 
rano"ement  of  the  teeth  have  been  noted  and  the  teeth  set  in  accordance 
therewith.  Frequently,  however,  the  slight  alteration  of  the  positions 
of  some  of  the  anterior  teeth  to  make  them  more  fully  accord  ^^^th  the 
principles  already  laid  down  for  their  arrangement,  will  be  suggested 
when  the  teeth  are  tried  in  the  mouth. 

Tlie  articulation  of  the  molar  and  bicuspid  teeth  in  the  excursions 
of  the  mandible  may  occasionally  rerjuire  slight  adjustment  because  of 
the  natural  iimitatioiis  in  articulators  already  noted.  A  systematic 
examination  of  the  dentures  in  place  in  the  mouth  should  be  under- 
taken according  to  a  method  recommended  by  O.  A.  Weiss/  First, 
the  occlusion  should  be  carefully  noted,  that  is,  it  should  be  ob- 
served whether  the  teeth  of  the  two  series  occupy  the  same  relation 
to  each  other  in  the  occlusal  position  of  the  jaw  as  they  did  in  the 
articulator.  A  possible  error  in  the  bite  may  be  ascertained  in  this 
way.  It  is  not  enough  to  depend  solely  upon  the  eye  to  judge  of 
this,  but  the  actual  contact  of  the  teeth  must  be  tested  by  means 
of  a  thin  instrument,  such  as  a  large  hatchet-shaped  excavator.  The 
patient  is  instructed  to  lightly  hold  the  jaw  in  tlie  position  of  occlusion. 
The  contact  of  the  dentures  anteriorly  is  first  tested  with  the  excavator. 
If  the  contact  is  uniform,  posteriorly  as  well  as  anteriorly,  prying  the 
teeth  apart  with  the  excavator  should  also  separate  the  distal  teeth. 
It  must  be  remembered,  however,  that  the  plates  are  to  be  held  firmly 
in  their  positions  upon  the  alveolar  ridges,  and  the  operator  should  not 
be  deceived  by  finding  the  plates  apparently  in  contact  posteriorly 
when  they  may  be  separated  in  front.  The  dentures  may  be  detached 
from  the  membrane  posteriorly,  the  teeth  apparently  being  in  contact, 
when  the  anterior  teeth  are  separated  by  this  measure.  The  contact  of 
the  distal  teeth  on  both  sides  should  be  tested  in  a  similar  manner. 
The  displacement  of  the  dentures  anteriorly  by  separating  the  poster- 
ior teeth  with  the  excavator  is  not  likely  to  occur  from  this  procedure. 

1  The  Dental  Review,  September,  1903. 


TRIAL   OF  THE  DENTURES.  449 

When  the  distal  teeth  are  separated,  the  jaws  shoiiM  be  pried  apart 
and  the  anterior  teeth  shoidd  also  be  similarly  separated.  This  should 
be  tested  on  both  sides.  If  a  serious  lack  of  adjustment  is  made  mani- 
fest by  this  trial,  the  bite  should  be  retaken  and  the  teeth  reset. 

In  testing  the  relation  of  the  teeth  in  the  various  movements  of  the 
mandible,  the  same  general  method  of  procedure  may  be  undertaken. 
The  patient  is  directed  to  move  the  mandible  to  the  right  and  bring  the 
teeth  in  contact  with  this  position,  the  condyle  on  that  side  remaining  in 
'  its  fossa.  On  the  right  side  the  two  lines  of  buccal  cusps  should  be  in 
contact,  while  at  the  same  time  the  lower  buccal  and  upper  lingual  are 
in  contact  on  the  left  side.  The  contact  is  to  be  tested  with  the  exca- 
vator unless  it  is  seen  that  the  teeth  do  not  occupy  these  relations.  If 
on  the  right  side  the  cusps  are  not  in  contact,  but  are  separated,  while 
they  touch  on  the  left,  it  is  evident  that  the  cusps  on  the  left  side  are 
too  prominent  or  that  those  on  the  right  side  are  not  sufficiently  so. 
This  defect  may  be  corrected  by  changing  the  inclination  of  the  long 
axes  of  the  teeth  on  the  left,  so  that  at  the  same  time  that  the  cusps  ou 
the  light  side  are  in  contact,  those  on  the  left  are  also. 

If,  on  the  contrary,  when  the  mandible  is  moved  to  the  right,  the  cusps 
on  that  side  are  in  contact  and  those  on  the  left  are  not,  the  long  axes  of 
the  teeth  on  the  left  should  be  altered  so  that  the  buccal  cusps  of  the  lower 
and  the  lingual  cusps  of  the  upper-are  made  more  prominent  and  come 
into  contact.  It  will  be  evident  that  these  alterations  must  be  made 
with  the  plates  in  their  place  upon  the  articulator,  and  without  altera- 
tion of  the  occlusal  relations  of  the  casts. 

This  operation  is  to  be  repeated  with  the  mandible  moved  to  theleft, 
and  any  adjustment  in  the  direction  of  the  long  axes  of  the  teeth  on 
either  side  made  in  accordance  with  the  above  principle. 

The  relation  of  the  teeth  when  the  jaw  is  protruded  for  incision 
should  be  tested.  The  patient  is  directed  to  bring  the  occlusal  edges  of 
the  incisors  into  contact  and  to  maintain  the  jaws  in  this  position.  The 
contact  of  the  distal  teeth  is  then  to  be  noted,  the  excavator  being  again 
employed  to  discover  if  they  touch.  If  the  molars  are  in  contact, 
as  determined  in  this  trial,  then  no  alteration  is  to  be  made  in  the 
position  of  the  teeth.  If  however,  they  are  not  in  contact,  it  will  be 
seen  either  that  the  overbite  of  the  upper  incisors  is  too  great  or  that 
the  compensating  curve  of  the  molar  and  bicuspid  teeth  does  not 
accord  with  the  path  of  the  condyle.  This  defect  may  be  corrected, 
either  by  reducing  the  overbite  until  the  incisor  and  distal  teeth 
are  in  simultaneous  contact  in  this  position  of  the  mandible,  or  by 
arranging  the  distal  teeth  with  a  compensating  curve  of  shorter  radius. 

If  in  the  protruded  position  of  the  mandible  the  anterior  teeth  are  not 
in  contact,  then  the  overbite  is  not  proportioned  to  the  compensating 
curve  and  the  length  of  the  cusps  of  the  distal  teeth;  or  the  compensat- 
ing curve  has  been  arranged  with  too  short  a  radius :  or  its  distal  end  is 
below  the  line  proper  for  the  compensating  curve.  Adjustment  of 
these  defects  may  be  made  and  the  dentures  returned  to  the  mouth  for 
confirmation  of  the  changes. 

29 


450  SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 

The  restoration  of  the  facial  contours  and  profile  by  the  dentures 
should  be  tested  at  this  time  also  and  any  alterations  which  may  be  in- 
dicated should  be  made. 


THE  ARRANGEMENT  OF  TEETH  IN  ABNORMAL  PROTRUSION 
OF  THE  LOWER  JAW. 

"In  the  preceding  illustrations  and  text  the  attention  of  the  student 
has  been  directed  to  normal  conditions,  and  the  normal  arrangement 
of  artificial  teeth  with  those  conditions,  in  order  that  he  may  familiar- 
ize himself  wnth  the  various  methods  and  principles  involved,  and  be 
able  to  modify  them  in  the  treatment  of  abnormal  cases. 

Fig.  410  show^s  an  extremely  abnormal  relation  of  the  alveolar  ridges 
and  one  requiring  a  considerable  modification  of  the  usual  methods  in 
order  to  arrange  the  teeth  in  a  manner  at  all  satisfactory.  A  protru- 
sion of  the  lower  jaw,  however,  within  certain  limits  may  be  met  v/ith 
occasionally,  and  a  normal  arrangement  of  the  teeth  obtained,  provid- 
ing that  other  conditions  are  favorable  to  it.  But,  before  attempting  to 
arrange  the  teeth  in  such  cases,  and  while  the  patient  is  still  at  hand, 
the  operator  must  make  some  careful  observations. 


Fio.    410 


Showing  extreme  protrusion  of  the'lower  jaw,  and  with  antaeonizing  casts  on  the  anatomical 

articulator. 


First,  to  ascertain  whether  the  lower  teeth  can  be  retracted  suffi- 
ciently to  obtain  an  overbite  without  interfering  with  the  movements 
of  the  tongue. 

It  is  seldom  possible  to  adjust  the  lower  teeth  toward  the  tongue  fur- 
ther than  the  centre  of  the  edentulous  ridge.  If  such  an  operation  is 
attempted,  the  movement  of  the  tongue  will  not  only  be  impeded  and 


ABNORMAL  PROTRUSION  OF  LOWER  JAW.  451 

speech  impaired,  hut  the  stabiHty  of  the  denture  will  be  affected  by 
the  tongue  constantly  pushing  against  it. 

Second,  it  must  be  ascertained  whether  the  tissues  of  the  upper  lip 
are  sufficiently  lax  to  permit  of  bringing  the  upper  teeth  to  the  necessary 
distance  forward  from  the  alveolar  ridge  to  obtain  an  overbite. 

Third,  will  the  removal  of  the  superior  incisor  teeth  from  the  alveolar 
ridge  cause  a  continual  loosening  of  the  denture  by  excessive  leverage 
on  these  teeth? 

Fourth,  whether  the  attempt  to  obtain  a  perfect  profile  will  effect  too 
radical  a  change  in  the  patient's  appearance. 

Fig.  411  illustrates  the  arrangement  of  teeth  necessary  in  case  of  pro- 
trusion so  extensive  as  in  Fig.  410.  The  upper  incisor  teeth  are  arranged 
to  close  inside  of  the  low^er,  with  their  labial  surfaces  gliding  closely 
on  the  lingual  surfaces  of  the  inferior  incisors,  the  incisive  function  be- 
ing performed  in  a  reverse  manner  to  that  of  a  normal  arrangement. 

When  the  upper  canine  tooth  is  reached,  the  first  attempt  is  made  to 
merge  into  a  normal  arrangement. 

This  tooth  i.s  placed  with  its  anterior  cutting  edge  covered  by  the 
lower  canine,  while  the  distal  cutting  edge  is  turned  labially  and 
ground  so  as  to  strike  directly  on  top  of  the  mesial  cutting  edge  of  the 

Fig.   411 


Showing  the  arrangement  of  tho  teeth  necessary  in  a  case  when  the  lower  teeth  close  outside  of  the 

upper. 

first  lower  bicuspid.  The  first  up})er  bicuspid,  is  ground  and  brought 
out  slightly  more  than  the  canine,  and  from  this  point  distally  the 
teeth  assume  their  normal  position.  In  order  to  obtain  a  graceful 
arrangement  in  such  a  case  as  seen  in  Fig,  411,  it  will  be  necessary 
to  do  considerable  grinding  and  lapping  of  the  upper  teeth,  which  is 
cot  at  all  unsightly  in  this  character  of  case. 

The  facial  expression  following  such  an  arrangement  of  the  teeth  will 
be  improved.  In  marked  protrusion  of  the  low^er  jaw,  where  the  nat- 
ural teeth  close  outside  of  the  upper  and  when  this  condition  has 
existed  up  to  middle  life  with  natural  teeth,  a  correction  of  the  facial 
expression  with  artificial  teeth  should  not  be  attempted."^ 

1  American  Text-Book  of  Prosthetic  Dentistry.    Second  Edition,  p.  -412. 


4ry2 


SELECTION,   ARRANGEMENT,  AND  ARTICULATION. 


THE  ARRANGEMENT   OF  TEETH  IN  ABNORMAL  PROTRUSION 
OF  THE   UPPER  JAW. 

In  the  arrangement  of  teeth  of  a  full  upper  and  lower  denture  in  pro- 
trusion of  the  upper  jaw,  it  is  seldom  possible  to  secure  the  ideal  re- 
lations existing  between  the  teeth  of  the  two  series  when  the  I'aws 
occup}-  a  normal  relationship.  In  most  instances  in  which  the  lower 
jaw  had  a  retruded  position  when  the  natural  teeth  were  in  place, 
after  their  loss, with  the  consequent  absorption  of  the  alveolar  process, 
the  increase  in  the  angle  of  the  mandible,  and  its  forward  movement,  a 
normal  relationship  between  the  two  series  cannot  be  obtained.  A  few 
cases  present  themselves,  however,  where  the  placing  of  the  artificial 
teeth  in  somewhat  the  same  relative  positions  occupied  by  their  natural 
predecessors  is  necessary.  In  these  cases  the  upper  anterior  teeth 
should  have  a  slight  lingual  inclination.     (Fig.  412.)     The  lower  an- 


FiG.  412 


Fin.  413 


Arrangement  of  the  teeth  in  protruding 
upper  jaw. 


Full  upper  denture  arranged  to  occlude  with 
lower  natural  teeth. 


terior  teeth  should  not  be  placed  in  occlusal  relations  with  them,  if  it 
is  necessary  to  give  them  a  labial  inclination.  The  lower  teeth  are 
to  be  made  to  bite  upon  the  lingual  surface  of  the  upper  plate. 
The  molar  and  bicuspid  teeth  are  to  be  articulated  according  to  the 
anatomical  principles  already  outlined,  wherever  this  is  possible.  In 
every  instance  the  cusps  should  be  made  to  interdigitate,  even  if  this  re- 
quires the  placing  of  the  lower  teeth  the  width  of  a  cusp  distal  to  their 
normal  position.  This  condition  of  occlusion  is  frequently  observed 
in  the  natural  dentures. 

The  commonest  cases  of  retruded  lower  jaw  which  present  for  treat- 
ment are  those  with  the  natural  teeth  remaining  in  position  and  pre- 
venting, by  the  nature  of  their  occlusion,  the  forward  movement  of  the 


A   FULL    UPPER  DENTURE  TO  NATURAL   TEETH.  453 

mandible.  In  these  instances  the  difficulties  of  obtaining  good  occlusal 
relations  between  the  teeth  are  greatly  increased,  and  usually  the  oper- 
ator has  to  be  satisfied  with  an  arrangement  far  short  of  the  ideal. 


THE  ARRANGEMENT  AND  ARTICULATION  OF  A  FULL  UPPER 
DENTURE  TO  NATURAL  TEETH. 

Cases  frequently  present  themselves  for  treatment  in  which  the  patient 
has  lost  all  of  the  upper  teeth,  while  all  or  a  large  number  of  the  lower 
remain  in  the  mouth.  While  the  general  principles  underlying  the  artic- 
ulation of  teeth  for  full  upper  and  lower  dentures  are  applicable  in  these 
cases,  certain  additional  considerations  are  to  be  noted. 

When  all  the  lower  natural  teeth  remain,  the  articulation  of  an  upper 
artificial  set  is  a  comparatively  simple  matter.  One  of  the  two  series  of 
teeth  is  in  place;  it  is  only  necessary  to  arrange  the  other  to  accord 
therewith.  While  it  is  usually  necessary  to  mount  the  casts  in  correct 
relation  with  the  joint  of  an  anatomical  articulator  which  has  been  set 
according  to  the  movement  of  the  mandible  for  the  case  in  hand, yet  the 
necessity  for  so  doing  is  not  so  great  as  in  full  dentures.  This  is  because 
of  the  fact  that  the  forms  of  the  occlusal  surfaces  of  the  natural  teeth  are 
eitherinaccord  with  the  jaw  movement,  usually  in  such  cases  having  been 
much  worn,  or  if  they  are  not,  they  cannot  be  altered,  and  the  form  of 
the  occlusal  surfaces  of  the  artificial  teeth  must  be  largely  determined  by 
them.  Still  it  is  preferable  to  use  the  anatomical  articulator,  because 
the  occlusal  relations  may  be  more  certainly  determined. 

In  the  arrangement  of  the  anterior  teeth  advantage  may  often  be  ob- 
tained by  placing  them  in  edge-to-edge  occlusion  with  the  lower  teeth. 
(Fig.  413.)  They  are  ground  to  articulate  upon  the  worn  edges  of  the 
lower  teeth  and  must  be  made  to  accurately  fit  these  edges  8.s  if  they 
had  been  worn  into  shape  in  the  mouth.  This  arrangement  enhances 
the  stability  of  the  plate  by  avoiding  the  leverage  due  to  an  overbite, 
but  is  not  possible  in  every  case,  because  the  distance  between  the  lower 
teeth  and  the  upper  alveolar  ridge  may  not  permit  the  placing  of  a  tooth 
of  the  proper  size.  Nor  is  it  indeed  always  advisable  from  consider- 
ations relative  to  appearance.  The  arrangement  of  the  artificial  teeth 
with  an  overbite  is  demanded  in  such  instances,  but  the  overbite 
should  be  as  short  as  possible.  Where  the  lower  jaw  occupies  a  re- 
truded  position,  however,  it  may  be  necessary  to  have  a  long  overbite 
with  a  Ungual  inchnation  of  the  upper  teeth,  but  in  such  instances,  a  firm 
retention  of  the  upper  plate  should  be  assured  and  a  space  left  be- 
tween the  upper  and  lower  teeth  to  avoid  displacement  of  the  upper 
denture. 

The  molar  and  bicuspid  teeth  should  be  ground  to  correspond  to  the 
state  of  wear  of  the  natural  teeth  and  should  be  made  to  occlude  evenly 
upon  them.  Many  dentures  of  this  type  are  seen  in  which  the  teeth  have 
been  articulated  without  alteration  of  their  form,  the  long  sharp  cusps 


454  SELECTION,   AHRAXdEMhWl',   AND   ARTK'ULATIOX. 

of  the  artificial  teeth  ocehuHiig  upon  much  abraded  lower  natural  teeth. 
The  functional  disadvantafje  of  such  an  arrangement  is  manifest. 

Where  only  the  lower  anterior  teeth  remain,  and  these  cases  are  of 
common  occurrence,  the  principles  already  laid  down  for  the  correct 
articulation  of  the  artificial  teeth  may  be  followed  out  almost  completely. 
It  will  be  remembered  that  the  lower  anterior  artificial  teeth  in  full 
dentures  are  the  last  ones  to  be  placed  in  position.  In  the  case  under 
consideration  the  natural  teeth  serve  as  a  starting  point  in  the  arrange- 
ment of  the  artificial  teeth,  which  latter  may  be  made  to  accord  with  the 
former.  The  slight  settling  of  the  lower  partial  denture  should  be  borne 
in  mind  and  anticipated  by  arranging  the  upper  teeth  just  short  of  occlu- 
sion with  the  natural  organs. 

This  type  of  case  illustrates  particularly  well  the  necessity  for  complete 
restoration  in  every  case  which  presents  itself.  In  these  instances  if 
the  lower  partial  denture  is  not  made,  the  whole  function  of  mastication 
is  thrown  upon  the  natural  teeth  and  the  upper  plate.  In  the  course  of 
time  the  pressure  upon  the  anterior  portion  of  the  upper  plate   will 

Fig.  414 


A  cast  showing  recent  extraction  of  six  anterior  teeth. 


cause  an  absorption  of  the  alveolar  process  underlying  it.  The  mucous 
membrane  in  the  anterior  part  of  the  upper  jaw^  will  become  soft  and 
spongy  and  re-adaptation  of  the  plate  may  be  necessary.  This  latter 
procedure  will  be  complicated  by  the  softness  of  the  tissues  over  the 
absorbed  process,  and  it  will  be  difficult  to  obtain  satisfactory  results. 
On  the  other  hand,  if  a  lower  partial  denture  had  been  inserted,  the 
condition  alluded  to  would  have  been  avoided. 

TEMPORARY  DENTURES. 

While  in  the  strictest  sense  of  the  term  all  dentures  are  temporary,  as 
greater  or  less  change  is  constantly  going  on  in  the  process,  reference  is 


TEMPORARY  DENTURES. 


455 


here  made  to  dentures  inserted  within  a  short  time  after  the  extraction 
of  the  teeth.  Temporary  dentures  are  to  be  advised  in  every  instance 
in  which  tliere  is  not  some  contraincHcating  condition.  They  may  be 
inserted  either  immediately  after  the  extraction  of  the  teeth  before  the 
inflammatory  reaction  incident  thereto  has  subsided,  or  they  may  be 
inserted  after  the  inflammation  has  ceased  and  before  the  resorption 
of  the  process  has  appreciably  progressed.  They  serve  to  provide  the 
patient  with  a  masticatory  apparatus  and  avoid  a  period  in  which  the 
patient  is  seen  without  teeth. 

The  selection  of  teeth  appropriate  for  these  cases  has  already  been 
discussed.  If  it  is  desired  to  insert  the  plate  immediately  after  the  ex- 
traction of  the  teeth,  an  impression  must  be  taken  and  a  cast  made  with 
the  natural  teeth  in  situ.  The  plaster  teeth  are  then  cut  from  the  cast, 
which  is  carved  to  represent  the  conditions  after  the  teeth  shall  have 
been  extracted.     The  anterior  artificial  teeth  are  to  be  mounted  in  the 


Fig.   415 


Showing  the  arrangement  of    teeth  necessary  in  a  case  like  Fig.  406,  where   the  six  anterior 
teeth  were  recently  extracted. 

sockets  of  the  natural  ones.  The  cast  is  carved  to  permit  this.  An- 
ticipating to  some  degree  the  absorption  of  the  external  plate  of  the 
process,  as  shown  in  Fig.  414,  the  artificial  teeth  are  to  have  the  portions 
which  are  to  be  in  relation  with  the  cast  so  ground  that  their  necks  pro- 
ject into  the  socket,  and  yet  after  the  external  plate  has  been  absorbed, 
they  will  be  in  relation  with  the  labial  surface  of  the  process.  The  distal 
teeth  are  to  be  mounted  in  the  usual  relation  with  the  alveolar  ridge. 
The  buccal  portion  of  the  plate  is  to  be  made  as  for  full  dentures,  but 
should  not  extend  farther  forward  than  the  centre  of  the  first  bicuspid. 
Of  course  no  portion  of  the  plate  is  to  extend  over  the  unresorbed  pro- 
cess anteriorly.     (Fig.  415.) 


456  SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 

PARTIAL  DENTURES. 

After  the  teeth  for  partial  cases  have  been  selected  in  accordance  with 
principles  already  outlined,  they  are  to  be  adjusted  in  their  proper 
])().sition  on  the  cast.  It  will  be  seen  that  there  is  less  latitude  in  their 
arrangement  than  exists  in  full  cases,  yet  their  correct  positions  with 
reference  to  the  natural  teeth  which  remain  may  be  more  readily  deter- 
mined. All  that  has  been  said  concerning  the  arrangement  of  teeth  to 
give  the  most  natural  appearance  applies  to  some  extent  to  the  setting  of 
teeth  for  partial  dentures. 

In  the  anterior  part  of  the  mouth,  gum  or  plain  teeth  are  to  be  used 
according  as  there  is  necessity  for  a  restoration  of  lost  gum  tissue  or  not. 
Before  the  teeth  are  placed  in  position,  the  cast,  in  relation  to  which  they 
are  to  be  placed,  is  to  be  scraped,  so  that  when  the  appliance  is  put  in  the 
mouth,  these  teeth  will  press  upon  the  mucous  membrane  and  imbed 
themselves  slightly  in  it.  The  gum  of  gum-section  teeth  is  to  blend 
with  the  natural  gum,  while  plain  teeth  are  to  be  made  to  appear  as  if 
growing  from  the  mucous  membrane.  The  teeth  are,  therefore,  to  be 
ground  to  accurately  fit  the  cast.  This  procedure  requires  considerable 
care  to  see  that  the  teeth  touch  the  cast  uniformly.  The  use  of  carbon 
paper  placed  between  the  cast  and  the  tooth  will  greatly  facilitate  the 
process  by  indicating  the  points  to  be  ground.  Nothing  short  of  an 
accurate  adaptation  of  surface  should  be  accepted.  It  is  usually  wise 
to  anticipate  the  resorption  of  the  process  in  the  front  of  the  mouth 
under  a  single  tooth  and  to  mount  it  on  the  cast  slightly  longer  than  its 
neighbors  with  this  in  view.  In  the  settling  of  the  plate,  which  occurs 
within  a  short  time,  the  tooth  is  made  of  correct  length. 

In  those  portions  of  a  partial  denture  where  gum  restoration  is  to  be 
made,  and  where  the  artificial  teeth  do  not  rest  upon  the  mucous  mem- 
brane, the  same  principles  which  apply  to  the  placing  of  teeth  for  full 
dentures  obtain.  Where  the  partial  plate  carries  more  than  a  few 
teeth,  the  setting  of  the  casts  upon  an  anatomical  articulator  and  the 
Fig.  416  articulation  of  the  teeth  according  to  methods  al- 

ready described,  are  indicated.     In  every  instance 
the  artificial  teeth  are  to   be  ground  so  that  they 
correctly  occlude  with  their  opponents.     In    the 
^    ^  ,     ,      ^ .  trial  of  the  artificial  dentures  in  the  mouth  the 

leeth  for  close  bite.  ,      .  n       i  i      •         i  i 

relation  of  the  teeth  in  the  several  positions  as- 
sumed by  the  jaw  in  mastication  is  to  be  tested,  and  where  a  cusp  in- 
terferes with  a  gliding  contact  of  the  teeth,  alteration  is  to  be  made. 

In  the  few  cases  in  which  it  is  deemed  advisable  to  open  the  bite,  it  is 
necessary  to  provide  for  the  contact  and  correct  functioning  of  the 
natural  teeth  which  have  thus  been  separated.  Where  these  are  molars 
and  bicuspids,  they  should  preferably  receive  crowns  whose  occlusal 
surfaces  should  be  made  to  accord  with  the  line  of  occlusion  of  the  teeth 
on  the  plate.  This  may  be  best  done  by  preparing  them  for  the  crowns, 
and  after  the  latter  have  been  constructed  and  temporarily  put  in  place, 


^ 


VOICE  AND  SPEECH  RELATIONS.  457 

the  bite  is  taken  with  the  jaws  in  their  new  position.     The  crowns  are 
removed  and  may  be  permanently  set  when  the  denture  is  inserted. 

Where  the  bite  is  very  close  in  cases  in  which  the  natural  teeth  almost 
touch  the  opposing  gum,  special  arrangement  must  be  made  to  secure 
sufficient  strength  for  the  artificial  teeth  in  this  location.  Where  the 
denture  is  to  be  of  vulcanite  and  sufficient  space  exists  for  a  reasonable 
thickness  of  the  plate,  the  use  of  a  long  bite  tooth  is  indicated.  If,  how- 
ever, only  one  tooth  is  to  occupy  the  space  under  such  conditions  as 
•  this,  it  is  preferable  to  use  a  plate  tooth  to  which  is  soldered  a  backing 
with  an  extension  as  shown  in  Fig.  408,  which  is  imbedded  in  the  vul- 
canite. This  gives  more  character  and  strength  than  if  a  vulcanite 
tooth  were  used.  If  the  plate  is  to  be  of  metal,  the  tooth  is,  of  course, 
directly  soldered  to  it. 

II.     VOICE  AND  SPEECH  RELATIONS. 

It  is  desired  that  artificial  dentures  shall  restore  any  lost  portions  of 
the  apparatus  necessary  in  the  production  of  articulate  speech,  and,  in 
addition,  shall  offer  no  impediment  to  the  normal  articulation  of  sounds. 
It  is  desired  also  that  they  shall  produce  the  least  possible  alteration 
in  the  tones  of  the  voice. 

It  has  been  seen  in  Chapter  IV.  that  the  loss  of  the  teeth  and  the 
changes  in  the  surrounding  tissues  incident  thereto,  cause  but  slight 
alteration  in  the  quality  of  the  voice,  that  speech  is  chiefly  affected  by 
these  conditions,  and  that  the  production  of  the  vowels  is  less  affected 
than  the  production  of  the  consonants.  It  was  seen,  further,  that  the 
chief  alterations  of  conditions  affecting  consonant  production  are  the 
loss  of  the  tissues  upon  which  the  current  of  air  is  projected,  or  of  those 
at  the  site  of  which  the  current  of  air  is  stopped,  and  the  loss  of  tissues 
concerned  in  the  formation  of  the  channel  through  which  the  air  is 
forced.  It  is  with  the  remedy  of  these  conditions  that  we  are  chiefly 
concerned,  and  at  the  same  time  the  artificial  denture  must  be  designed 
to  offer  the  least  possible  impediment  to  the  articulation  of  all  sounds. 

Slight  alterations  of  the  tones  of  the  voice  will  occur  when  any  ar- 
tificial denture  is  placed  in  the  mouth  of  a  patient.  These  are,  in  many 
instances,  so  slight  as  to  be  indistinguishable,  while  in  others  the  differ- 
ence may  be  sufficient  to  be  appreciated.  This  consideration,  however, 
is  of  comparatively  small  importance  in  the  design  of  dentures,  for  the 
reason  that  it  is  impossible  to  place  an  appliance  of  any  sort  in  the 
mouth  without  producing  some  slight  changes  in  the  voice  tones.  Thin- 
ness of  the  plate  which  covers  the  palatal  vault  contributes  more  than 
anything  else  to  a  retention  of  the  normal  voice  qualities.  It  is  for 
this  reason  that  the  swaged  metal  plate  causes  less  change  than  a  plate 
of  one  of  the  molded  bases. 

In  designing  a  denture  to  fulfil  all  the  requirements  of  speech  the 
following  fact  must  be  noted:  the  factors  concerned  in  the  speech 
relations  of  a  denture  are  the  form,  location,  and  arrangement  of  the 


458  SELECTIOS,   ARRANGEMENT,  AND  ARTICULATION. 

teeth,  and  the  Ungual  conformation  of  the  upper  and  lower  dentures. 
These  factors  are  to  be  so  adjusted  to  the  case  in  hand  as  to  permit  a 
free  movement  of  the  tongue,  and  the  correct  formation  of  the  air 
channel,  and  provide  for  the  obstruction  of  the  air  current  at  the  proper 
places. 

Fortunately  the  form  and  arrangement  of  the  teeth  to  answer  the 
requirements  of  appearance  and  food  preparation,  in  general,  best  serve 
the  ends  to  be  desired  from  the  standpoint  of  speech  production.  There 
are  a  few  exceptions  to  this  principle  which  are  to  be  noted.  The 
arrangement  of  the  upper  and  lower  anterior  teeth  with  a  slight 
space  between  them  to  prevent  contact  and  consequent  displacement 
of  the  denture,  recommended  by  some  practitioners,  interferes  occa- 
sionally with  the  articulation  of  the  sounds  in  which  the  current  of  air 
is  interrupted  at  this  point.  The  tongue  is  called  upon  to  close  up  the 
deficiency  caused  by  a  lack  of  contact  of  the  teeth  in  the  production  of 
the  sound,  for  example,  an  adjustment  which  it  is  usually  possible  for  it 
to  execute. 

The  bicuspids  and  molars  for  considerations  of  plate  stability  fre- 
quently intrude  upon  the  space  required  by  the  tongue  in  its  adjust- 
ments; a  consequent  cramping  of  this  organ  occurs  with  a  certain 
thickness  of  speech  which  persists  until  the  individual  has  adapted 
himself  to  the  abnormal  conditions. 

Freedom  in  the  movement  of  the  tongue  may  some  times  be  prevented 
by  an  impingement  of  the  plate  upon  its  frienum.  It  has  already  been 
seen  that  this  condition  is  to  be  avoided  upon  another  ground — that  of 
the  displacement  of  the  denture. 

A  common  error  in  the  conformation  of  the  lingual  surface  of  lower 
plates  causes  a  limitation  to  the  movement  of  the  tongue.  Where  the 
lower  molars  and  bicuspids  are  placed  to  the  lingual  side  of  the  ridge 
to  occlude  with  those  of  the  upper  jaw  in  mouths  in  which  great  resorp- 
tion of  the  process  has  occurred,  the  narrowness  of  the  plate  restricts 
the  tongue  movements  necessary  to  correct  articulation.  It  not  in- 
frequently happens  that  the  lower  plate  itself  intrudes  upon  the  space 
proper  for  the  tongue.  These  conditions  are  to  be  avoided  if  possible. 
It  is  often  necessary  to  compromise  the  demands  of  ])late  stability  with 
those  of  speech  production.  This  situation  arises  in  a  large  number 
of  lower  dentures  constructed  for  mouths  in  which  considerable  re- 
sorption of  the  process  has  occurred.  In  these  instances  the  arch  of 
the  teeth  should  be  as  wide  as  is  consistent  with  plate  stability,  and  at 
the  same  time  the  lingual  surface  of  the  lower  plates  should  be  made  as 
concave  as  possible  to  provide  adequate  space  for  the  tongue. 

When  the  lingual  conformation  of  the  upper  plate  copies  as  accurately 
as  possible  the  form  of  the  natural  tissues,  the  conditions  most  favor- 
able to  articulation  are  established.  Large  numbers  of  vulcanite  den- 
tures are  made  with  a  smooth  dome-shaped  lingual  surface,  to  which 
the  tongue  can  adapt  itself  in  the  formation  of  the  air  channel  with  less 
ease  than  if  the  conformation  of  the  natural  tissues  were  reproduced. 


VOICE  AND  SPEECH  RELATIONS.  459 

In  the  formation  of  the  TH,  T,  D,  S,  SH,  C,  Z,  ZH  sounds,  the  sides 
of  the  tongue  are  curled  up  to  come  in  contact  with  the  teeth  and 
adjacent  alveolar  process  to  form  the  channel  through  which  the  aii 
escapes.  It  has  been  seen  that  the  form  of  this  channel  largely  de- 
termines the  consonant  sounds.  While  the  tongue  can  adapt  itself  to 
changed  relations  of  other  tissues  taking  part  in  the  formation  of  this 
channel,  as  the  enunciation  of  patients  wearing  dentures  constructed 
regardless  of  these  conditions  abundantly  testifies,  yet  it  is  not  wise  to 
impose  too  much  upon  the  tongue  in  this  way.  The  more  nearly  the 
lingual  surface  of  the  plate  corresponds  to  the  form  of  natural  tissues, 
the  more  readily  will  the  tongue  be  capable  of  afi^ecting  correct  adjust- 
ment to  them.  With  this  end  in  view  it  is  advisable  in  vulcanite 
dentures  to  reproduce  the  lingual  surfaces  of  the  teetli,  either  by  the  use 
of  counter-sunk  pin  teeth  or  by  the  imitation  of  these  surfaces  with  the 
vulcanite.^  (Fig-  417.)  The  imitation  of  the  rugae  on  the  lingual  surface 
is  to  be  referred  to  presently. 

Fig.  417     • 


Lingual  surfaces  of  teeth  reproduced  in  vulcanite.     (Fine.) 

The  projection  upon  the  lingual  surface  of  a  metal  plate  caused  by  the 
vacuum-chamber  seldom  interferes  with  correct  speech  production. 
This  is  for  the  reason  that  if  properly  located  and  of  only  the  required 
depth,  it  does  not  prevent  the  formation  of  a  sufficiently  large  channel 
for  the  air.  The  tongue,  of  course,  has  to  adjust  itself  to  this  condition 
of  affairs,  but  the  adjustment  is  made  with  comparative  ease.  Further- 
more, if  properly  located,  the  vacuum-chamber  is  posterior  to  the  point 
of  interruption  of  the  air  channel  in  the  formation  of  the  T,  D,  S,  C,  Z, 
SH  and  CH  sounds. 

The  conformation  of  the  lingual  surface  of  the  upper  plate  to  facili- 
tate correct  speech  has  been  well  described  by  Dr.  George  B.  Snow. 
The  following  is  requoted  from  a  paper  pubhshed  in  the  Dental  Ad- 
vertiser in  1899.  "Trouble  is  often  experienced  by  patients  in  secuiing 
a  clear  and  sharp  S  sound  after  they  have  commenced  the  use  of  artifi- 
cial dentures.  A  peculiar  whistling  sound  is  produced.  It  is  now  pro- 
posed ±0  give  a  short  description  of  the  mechanism  by  which  these 
sounds  are  produced,  and  to  draw  attention  to  the  importance  of  giving 

J-  Dr.  W.  M.  Fine,  International  Dental  Joiimal. 


460 


SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 


due  consideration  to  the  shape  of  the  lingual  side  of  the  plate,  if  it  is 
desired  to  secure  clearness  and  ease  of  articulation  of  the  sound  above 
referred  to. 

Inspection  of  uiodels  of  the  upper  jaw  in  which  the  natural  teeth  are 
in  place  will  show  that  while  the  lin<^ual  surface  of  the  bicuspids  and 
molars  practically  forms  a  continuation  of  the  lateral  curve  of  the 
palatal  arch,  the  alveolus  behind  the  incisors  is  thickened.  With  the 
rugfe  a  nearly  triangular  space  is  oftened  produced,  bounded  by  a  line 
connecting  the  distal  surfaces  of  the  laterals  and  the  edges  of  the  alveo- 
lar sockets.  Viewed  in  longitudinal  section,  a  reversed  curve  is  pre- 
sented, extending  forward  from  the  hard  palate  and  merging  into  the 
hollow  outline  of  the  lingual  surfaces  of  the  incisors. 

Sections  of  models  from  different  mouths  are  shown  in  Figs.  418  to 
423.  The  curves  will  be  seen  to  present  nearly  the  same  general  shape, 
whether  the  arch  be  deep,  like  Fig.  419,  or  shallow,  like  Fig.  421. 


Fig.  418 


Fig.  419 


Fig.  420 


Fig.  421 


Sections  through  casts  showing  thickened  alveolus  back  of  incisor"?. 

In  Figs.  422  and  423  an  attempt  has  been  made  to  show  the  relative 
positions  of  the  tongue  and  teeth  in  making  the  S  and  SH  sounds.  In 
producing  the  SH  sound  (Fig.  423),  the  upper  and  lower  teeth  are  held 
slightly  apart;  the  tip  of  the  tongue  rests  against  the  gum  behind  the 
lower  incisors,  its  edges  impinging  upon  the  lingual  surfaces  of  the 
bicuspids  and  molars  at  their  junction  with  the  alveolus.  The  result  is  a 
narrow  passage  over  the  centre  of  the  tongue,  the  narrowest  portion 
being  just  back  of  its  tip,  the  passage  being  thus  gradually  enlarged 
both  behind  and  before  its  narrowest  portion.  The  breath,  being 
forced  through  this  narrow  passage,  follows  its  curve,  and  is  impelled 
again.st  the  tips  of  the  lower  incisors,  the  result  being  the  SH  sound. 

In  giving  the  S  sound  (Fig.  422,  all  the  parts  remain  in  the  positions 
above  described,  except  the  tip  of  the  tongue,  which  is  curved  upward 
to  the  alveolar  border  on  the  lingual  side  of  the  upper  incisors,  making 
the  passage  smallest  at  its  outlet  and  projecting  the  current  of  air 
against  the  upper  incisors.  It  will  be  found  by  experiment  that  if  the 
tongue  is  drawn  backward  a  little  from  the  position  described,  the  his- 


VOICE  AND  SPEECH  RELATIONS. 


461 


sing  sound  will  be  changed  to  a  whistle.  It  will  be  noticed  that  the 
shape  of  the  palatine  arch  is  such  that  the  tongue  can  readily  conform 
to  it,  and  that  the  passage  between  the  tongue,  palate,  and  alveolar 
border  can  be  readily  formed,  by  which  a  clear  articulation  of  the 
sounds  in  question  can  be  produced. 

As  a  contrast  to  the  figures  already  shown,  attention  is  directed  to 
Fig.  424,  which  is  a  section  of  a  fairly  weirmade  vulcanite  plate.  The 
teeth  are  well  arranged,  the  joints  close  and  well  fitted,  the  finish  good. 


Fig.  422 


Fig.  423 


Position  of  tongue  in  pronouncing  S. 


Position  of  tongue  in  pronouncing  SH. 


It  will  be  observed  that  the  palatal  curve,  if  continued,  would  meet  and 
coincide  with  the  curve  of  the  lingual  surfaces  of  the  incisors,  there  being 
a  break  at  the  point  of  junction  of  the  teeth  and  rubber;  and  this  is  so 
abrupt  that  it  would  be  impossible  for  the  tongue  to  follow  its  outline, 
as  it  does  the  curve  of  the  natural  arch  in  Figs.  422  and  423.  The 
reversed  curve,  shown  in  Figs.  418-421,  is  plainly  out  of  the  question. 
The  sketch  illustrates  what  is  by  no  means  an  extreme  case.  With 
thinner  teeth  and  a  longer  bite  the  defect  noted  would  be  still  greater. 


Fig.  424 


Fig    425 


Section  through  vulcanite  plate.  Section  through  vulcanite  plate  designed 

to  imitate  contour  of  alveolar  process  back 
of  incisors. 

If  the  plate  which  is  shown  in  section  in  Fig.  424  were  filled  in  to  pre- 
sent the  outline  shown  in  a  dotted  line  in  Fig.  425,  the  enunciation  of 
the  wearer  would  be  improved,  and  another  very  substantial  benefit  be 
secured,  viz.,  an  amount  of  strength  which  will  obviate  any  danger  of 
the  plate  cracking  through  the  centre. 

If  the  imitation  of  nature  be  carried  far  enough  to  reproduce  the  rugee 
upon  the  plate,  it  will  be  found  to  be  a  decided  benefit  both  to  articu- 
lation and  in  the  management  of  food  in  mastication.     When  the  lin- 


462  SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 

gual  side  of  the  plate  Is  smooth,  the  tongue  has  but  Httle  power  to  hold  a 
morsel  of  food  upon  it,  while  with  the  rugae  the  food  is  easily  held  and 
managed.  They  are  easily  formed  by  burnishing  a  piece  of  heavy  tin 
foil  over  a  model  showing  them  prominently,  filling  the  depressions  in 
the  tin  foil  with  wax  or  paraffin,  and  then  fitting  and  attaching  it  to  the 
trial-plate  when  waxed  up  and  ready  for  flasking,  leaving  its  edges 
turned  up  so  that  it  will  be  held  securely  in  the  plaster  when  the  plate 
is  flashed.  The  surface  of  the  vulcanite  will  come  out  clean  and  smooth, 
and  will  require  but  little  polishing.  It  will  be  found  that  a  patient 
who  has  once  become  accustomed  to  the  use  of  a  plate  made  as  above 
suggested  will  be  extremely  loath  to  return  to  the  use  of  one  as  ordina- 
rily made." 

III.     THE  RELATION  OF  PLATE  DENTURES  TO  THE 
EXPRESSIVE  MOVEMENTS  OF  THE  FACE. 

Beside  restoring  the  fixed  expression  of  the  face,  plate  dentures  must 
establish  conditions  which  admit  of  the  normal  activity  of  its  expres- 
sive movements.  It  has  been  shown  in  Chapter  IV.  that  the  following 
conditions  resulting  from  the  loss  of  the  teeth  afl^ect  these  move- 
ments: a  change  in  the  relation  of  the  jaws  and  the  withdrawal  of 
the  normal  support  provided  by  the  teeth  and  alveolar  process  for 
the  lips  and  cheek;  the  restriction  of  the  movement  of  the  lips  and 
cheeks  in  the  associated  group  of  muscular  movements  wdiich  give  ex- 
pressional  sijjnificance  to  the  face.  Artificial  dentures  are  to  establish 
such  conditions  as  will  permit  the  normal  operation  of  these  move- 
ments. 

In  the  design  of  the  dentures  to  answer  the  above  mentioned  re- 
quirements, the  following  factors  are  to  be  considered  as  promoting  the 
desired  ends.  The  relation  between  the  jaws  is  established  in  the 
position  of  occlusion  by  the  dentures.  The  support  of  the  lips  and 
cheeks  is  furnished  by  the  positions  of  the  teeth  and  the  contours  of  the 
buccal  and  labial  surfaces  of  the  plates. 

While  the  correct  operation  of  the  muscular  activities  concerned  in 
the  expressive  movements  in  which  the  mouth  participates,  is  largely 
provided  for,  if  the  dentures  answer  other  requirements  imposed  upon 
them,  it  is  necessary  to  call  attention  to  the  features  of  the  dentures 
directly  concerned  in  this  relationship,  in  order  that  in  the  pro- 
motion of  other  purposes  these  considerations  shall  not  be  infringed 
upon.  As  with  natural  dentures,  the  lips  should  be  capable  of  free  and 
easy  movement  over  the  teeth  and  the  labial  surfaces  of  the  plates. 
The  margins  of  the  dentures  and  its  external  contours  should  not  en- 
croach upon  the  line  of  action  of  any  of  the  muscles  concerned  in  these 
movements.  The  labial  contours  of  the  plates  and  the  teeth  should 
support  the  lips  in  those  positions  wdiich  are  subsequently  discussed  as 
proper  for  the  establishment  of  the  fixed  expressions  of  the  face.  They 
should  permit  an  easy  gliding  of  the  lips  over  them  upon  the  contrac- 
tion of  the  various  muscles  centering  in  the  orbicularis  oris. 


RESTORATION  OF  FACIAL  EXPRESSION.  463 

The  upper  plate  is  the  one  mostly  concerned  in  this  relationship. 
Its  upper  margin  should  not  impinge  upon  the  attachments  of  the 
orbicularis  oris  in  the  incisive  fossae.  At  the  position  of  the  canine  tooth 
there  should  be  enough  of  a  prominence  to  afford  a  'point  d'appui  for 
the  muscles  elevating  and  retracting  the  corner  of  the  mouth.  The 
upper  margin  of  the  plate  should  not  be  so  thick  as  to  prevent  a  direct 
line  of  action  in  the  elevation  of  the  lip  by  the  levator  labii  superioris 
alffique  nasi  and  the  levator  labii  superioris  proprius. 

The  lower  denture  should  avoid  in  its  anterior  margin  the  line  of 
action  of  the  levator  labii  inferioris,  which  is  placed  to  the  side  of  the 
median  line  of  the  symphysis. 

An  incorrect  relation  between  the  jaws  would,  of  course,  cause 
a  limitation  of  these  movements,  if  the  distance  established  was  too 
great  or  too  small,  and  too  great  or  too  little  prominence  to  the  plates 
underlying  the  lips  would  cause  a  similar  limitation  to  the  expressive 
movements  of  the  mouth.  It  will,  of  course,  be  seen  that  the  conditions 
necessary  for  the  correct  operation  of  the  movements  concerned  in  ex- 
pression, have  been  provided  for  by  other  considerations  relative  to  the 
dentures.  These  several  demands  have  overlapped  in  this  particular 
and  the  necessity  for  the  correct  construction  of  the  dentures  is,  there- 
fore, increased. 

IV.     THE  RESTORATION  OF  FACIAL  EXPRESSION. 

The  alteration  in  facial  expression  which  succeeds  the  loss  of  the 
teeth  has  been  described  in  Chapter  IV.  One  of  the  chief  functions  of 
artificial  dentures  is  to  restore  this.  By  the  insertion  of  artificial  den- 
tures the  relation  between  the  jaws  should  be  correctly  established,  the 
contours  of  the  lips  and  cheeks  restored,  and  the  teeth  and  those  por- 
tions of  the  gum  visible  in  the  movements  of  the  lips  restored  as  nearly 
as  possible  to  their  original  appearance.  The  various  steps  in  the  de- 
sign and  construction  of  the  dentures  which  have  already  been  described 
have  served  to  promote  these  ends. 

The  relation  between  the  jaws  in  the  position  of  occlusion  is  estab- 
lished when  the  bite  is  taken.  At  this  time  also  a  tentative  fulness 
.  which  the  plates  should  possess  to  restore  the  lips  and  cheeks  to  their 
original  contours,  is  obtained.  In  the  arrangement  of  the  artificial 
teeth  the  portions  of  the  dentures  visible  in  laughing  and  smiling  are 
arranged  so  that  the  teeth  correctly  harmonize  with  the  other  features 
of  the  face.  The  court  of  final  resort  in  determining  the  efficacy  of 
these  several  measures  should  be  the  actual  trial  of  the  dentures  in  the 
mouth.  It  is  now  proposed  to  discuss  the  various  details  of  the  den- 
tures which  are  related  to  the  restoration  of  facial  expression. 

The  primary  object  which  artificial  dentures  should  have  from  the 
cosmetic  standpoint  is  the  establishment  of  the  appearance  which  the 
patient  would  have  if  the  natural  teeth  had  remained.  This  is,  of 
course,  however,  subject  to  the  sHght  exceptions  which  have  already 


464  SELECTION,  ARRANGEMENT,  AND  ARTICULATION. 

been  mentioned  in  tills  eluipter,  but  in  the  main,  this  is  the  purpose  in 
view.  It  has  ah-eady  been  shown  that  compk'te  data  for  the  execution 
of  this  motive  are  lacking  in  nearly  every  instance.  The  circumstances 
most  favorable  for  the  exact  establishment  of  such  a  condition  are  the 
recent  extraction  and  preservation  of  the  teeth  of  the  patient  for  re- 
ference, and  the  possession  of  photographs  taken  shortly  before  the 
teeth  were  lost.  Even  to  these  data  must  be  added  an  allowance  for 
the  effects  ensuing,  if  an  appreciable  period  has  clasped  between  the 
restoration  and  the  time  to  which  the  original  data  referred. 

For  the  most  part  the  restoration  of  appearance  must  be  undertaken 
with  data  secured  at  the  time  the  dentures  are  made,  which  are  the  only 
source  of  reference.  These  data  are  to  be  obtained  almost  solely  from  the 
patient.  They  may  be  occasionally  supplemented  by  reference  to  other 
members  of  the  family  of  the  patient,  whose  physical  similarity  so  cor- 
responds as  to  make  their  use  of  service.  A  brother  or  sister,  for  example, 
or  a  son  or  daughter,  may  sometime  be  possessed  of  characteristics  re- 
sembling those  of  the  lost  tissues  of  the  patient  which  will  furnish 
reliable  information  in  these  particulars.  The  accuracy  of  this  resem- 
blance should  be  positively  ascertained  before  it  is  utilized  for  this  pur- 
pose. Some  general  considerations  relating  to  the  restoration  of  facial 
expression  may  not  be  out  of  place. 

While  the  majority  of  faces  which  require  restoration  by  prosthetic 
means  cannot  by  any  artifice  be  made  to  correspond  to  the  regular  con- 
ditions of  profile  and  contour  established  by  the  ideals  of  art,  yet  these 
latter  should  be  a  possible  goal,  nearness  of  approach  to  which  is  only 
limited  by  the  particular  conditions  found  in  the  individual  case.  The 
attainment  of  this  ideal  is  neither  to  be  hoped  for  nor  expected,  because 
of  the  natural  limitations  which  the  conditions  of  each  case  impose. 
In  the  lack  of  definite  information  as  to  the  conditions  originally  ex- 
istent in  the  individual  case,  the  effort  should  be  to  exhaust  the  in- 
formation furnished  by  the  tissues  as  to  the  original  condition,  and  then 
to  complete  the  restoration  along  lines  consistent  with  the  artistic  ideals. 

The  student  will  find  the  following  quotation  from  John  W.  ^^ander- 
poel's  "  Drawing  and  Construction  of  the  Human  Figure  "  *  of  value 
in  arranging  the  contours  of  the  lips,  and  should  read  it  in  connection 
with  Figures  426  and  433,  which  illustrate  a  patient  with  correct  facial 
contours  established  by  a  full  upper  and  lower  denture.  He  says, 
"  Beginning  with  the  front  view,  note  the  convexity  of  the  mass  of  the 
mouth  as  affected  by  the  teeth  ;  this  means  that  as  the  corners  are 
farther  back  than  the  middle,  the  curvature  of  both  lips  in  their 
approach  to  the  corners  partakes  of  foreshortening.  Irrespective  of 
the  view,  establish  the  relation  of  the  corners  to  the  middle.  This 
is  exceedingly  important,  as  it  relates  to  symmetry  in  its  construction 
and  action,  as  well  as  to  expression  and  character.  In  a  normal  mouth 
the  corners  are  slightly  lower  than  the  middle.  Though  the  mouth  is 
convex  in  the  mass  (except  at  the  corners  where  the   lips  dip  into  a 

iThe  Sketch  Book,  July,  1903.  p.  25. 


REiiTOILlTfON   OF  FACIAL   EXPRESSION. 


465 


deprossion),  it  is  dili'erently  expressed  in  cacli  lip.  The  inucoiis  por- 
tion of  the  up])er  lip  is  divided  into  two  ccpuil  parts  or  planes,  of 
greatest  width  in  the  middle,  retreating  in  diminishing  thiekness  with 
a  downward  course  to  the  depressed  corners.  The  lower  lip  on  the 
other  hand  contains  three  planes,  the  central  one  extending  well  on 
each  side  of  the  middle  of  the  upper  lij),  and  flanked  by  a  minor  one 
on  each  side,  rising  to  an  acute  angle  at  the  corner.  The  planes  of 
the  upper  lip  are  comparatively  flat,  while  those  of  the  lower  are  very 
convex. 

The  length  of  the  upper  li})  has  its  origin  at  the  middle  cartilage  of 
the  nose  in  the  form  of  a  depression,  which  widens  as  it  descends,  and 
terminates  in  the  delicate  angle  of  the  middle  of  the  upper  lip  :  the 
centre  of  this  angle  forms  the  most  forward  part  of  the  mouth.     This 


Fic.  426 


Profile  view  of  correct  facial  contours  established  with  artificial  dentures 


angle  is  repeated  in  the  contact  of  the  upper  lip  with  the  lower  im- 
mediately below  this  point,  although  the  angle  is  more  obtuse  and  a 
little  flattened,  showing  how  the  upper  lip  clasps  the  lower  as  it  over- 
hangs it.  The,  lower  lip  rolls  outward  and  is  apt  to  be  full  and  convex 
in  proportion  as  the  concavity  below  it  is  deep.  This  depression  or 
length  of  the  lower  lip  divides  perceptibly  and  forms  at  its  base  the 
upper  border  of  the  chin.  Through  a  study  of  the  profile,  which  is 
equivalent  to  the  section,  these  facts  are  more  easily  understood.  Note 
first  the  backward  sloping  plane  from  the  nose  to  the  base  of  the  chin, 
and  in  it  find  a  series  of  steps,  the  upper  lip  overhanging  the  lower 
and  the  lower  the  chin.  Note  the  concavity  in  the  length  of  both  lips, 
and  the  convexity  of  their  breadth  or  mucous  portion,  greater  in  the 
lower — at  least  more  rolling — all  subtly  connected  with  the  adjacent 
parts  of  the  face,  particularly  in  the  soft  play  at  the  corners."  .... 
"  However  the  student  must  fully  realize  that  no  matter  how  intimate 
CO 


466 


SELECTIOX,  ARRANGEMENT,  AND  ARTICULATION. 


his  knowledge  of  a  part  may  be,  it  is  only  of   value  when  it  coexists 
with  an  appreciation  of  its  relation  to  the  entire  structure." 

The  regular  profile  above  described  is  tiiat  obtaining  only  with  in- 
dividuals the  antero-posterior  relation  of  whose  jaws  produces  it.  As 
the  prosthetist  has  no  control  over  the  antero-posterior  position  of  the 
mandible  in  his  restorations,  it  is  only  in  the  cases  in  which  this  is 
normal  that  he  may  attempt  to  establish  the  relation  of  the  lips 
which  is  shown  to  be  harmonious  with  such  a  jaw  relationship.  He 
should  take  note,  however, of  the  commonly  observed  principle  of  profile 
that  a  projection  of  the  lips,  which  is  caused  by  a  projection  of  the 
teeth  and  process,  is  commonly  associated  with  a  receding  forehead,  and 
that  in  those  individuals  possessed  of  a  more  marked  development  of  the 


Fig.  427 


Fig.  428 


Front  view  of  patient  with  full  upper  and 
lower  artificial  dentures  in  place  showing 
restoration  of  facial  contours.  Same  pat- 
ient as  in  Figs.  225  and  226. 


Profile  view  of  patient  showing  restoration 
of  facial  profile.  Same  jjatient  as  in  Fig.  225 
and  226. 


frontal  region  in  which  the  facial  angles  are  more  nearly  approximate 
9'^°,  there  is  less  protrusion  of  the  lips. 

The  conditions  of  contour  of  the  lips  affecting  the  profile  commonly 
observed  in  individuals  with  the  jaw  anterior  or  posterior  to  the  above 
described  relationship,  should  be  observed.  A  common  type  of  face 
observed  in  America  is  that  with  a  retruded  chin.  In  these  cases  the 
positions  of  the  lips  are  altered  from  that  above  described  to  accord 
with  such  a  position  of  the  mandible.  This  type  of  face  is  shown  in 
Fig.  430.  It  will  be  .seen  by  reference  to  this  figure  that  the  lips  oc- 
cupy approximately  the  same  relation  with  a  line  drawn  from  the  ba.se 
of  the  nose  to  the  chin  as  they  occupy  in  Fig.  426.  In  all  cases  where 
the  jaw  occupies  this  po.sition  this  relation  of  the  lips  should  be 
obtained.    The  upper  lip  must  frequently  be  made  sUghtly  more  promi- 


RESTORATION  OF  FACIAL  EXPRESSION. 


467 


nent,  but  this  only  to  be  done  when  the  contours  of  the  alveolar  pro- 
cesses demand  it.     (Figs.  429  and  430.) 

Cases  are  of  less  frequent  occurrence  in  which  the  mandible  is  pro- 
truded. In  an  edentulous  case  of  this  character,  beside  the  observed 
relationship  between  the  alveolar  processes,  the  prominence  of  the  cheek 
over  the  ramus  of  the  jaw  contributes  to  aid  in  the  diagnosis.  In  such 
instances  the  curves  of  the  lips  observed  in  cases  with  a  normal  jaw 
relationship  do  not  exist.  This  is  because  of  the  nature  of  the  support 
afforded  the  lips  by  the  process  and  the  differently  inclined  teeth  and 
because  of  the  muscular  action  which  has  been  necessary  to  keep  the 
lips  closed.  In  such  instances,  therefore,  the  prosthetist  can  only,  of 
course,  hope  to  establish  conditions  of  profile  which  were  as  good  as 
those  exi&ting  before  the  loss  of  the  teeth. 


Fig.  429 


Fig.  430 


Front  view  of  patient  with  full  upper  denture  in 
place,  showing  restoration  of  facial  contours 


Profile  view  of  patient  with  retruded  chin: 
full  upper  artificial  denture  in  place. 


At  the  age  at  which  artificial  dentures  are  commonly  necessary  the 
full  and  rounded  contours  characteristic  of  youth  have  usually  faded. 
In  indi^dduals  of  this  age  who  have  not  lost  their  teeth  these  effects  are 
likewise  observable.  The  prosthetist,  therefore,  should  take  into  account 
in  his  restorations  the  effect  wdiich  age  produces  upon  both  profile  and 
contours,  and  should  establish  these  in  accordance  thercAvith.  A 
patient  exhibiting  the  effects  of  the  passage  of  time  upon  other  fixed 
features  of  the  face,  yet  displaying  oral  contours  belonging  to  a  previous 
period  of  life,  would  be  an  inexcusable  anomaly. 

The  effect  of  age  in  the  absorption  of  the  subcutaneous  fat,  in  the 
atrophy  of  the  skin,  and  the  establishment  of  wrinkles  in  the  face,  has 
been  described  in  Chapter   IV.      No  attempt,  therefore,  in  the  pros- 


468 


sKLhVTioy,  ARRAy(;KMj:yT,  Ayn  articulation. 


thetic  restoration  sliould  he  made  to  alter  the  conditions  clearly  attrihut- 
ahle  to  this  influence.  The  lines  about  the  mouth,  for  example,  which 
have  resulted  from  age,  are  not  to  be  altered,  while  those  which  have 
ensued  from  the  loss  of  the  teeth  are  to  be  corrected  as  far  as  the  pro- 
thetist  is  able. 

Finally,  the  prothetist  should  utilize  every  minutia  of  information  to 
be  obtained  from  the  patient  and  from  the  conditions  of  the  tissues 
about  the  mouth.  A  full  knowledge  of  the  influence  of  time  and  of  the 
influence  of  the  loss  of  the  teeth  should  be  in  his  luuKls,an(l  his  efforts 
should  be  directed  toward  the  re-establishment  of  conditions,  alteration 
of  which  has  produced  the  observed  changes. 


Fir.    431 


Fig.   r.Vl 


m. 


Full  upper  denture  with  elongate  centrals, 
slightly  inclined  lingually.  Same  patient  as 
Figs.  429  and  430. 


Patient  with  full  upper  denture:   incisors 
irregularly  arranged. 


In  discussing  the  details  of  the  restoration  of  the  contours  of  the  mouth 
and  cheeks,  simplicity  will  be  consulted  by  considering  first  the  profile 
and  then  the  contours  of  the  face  as  viewed  from  the  front.  In  estab- 
lishing the  profile  in  accordance  with  the  principles  above  outlined  the 
following  factors  are  to  be  taken  into  account:  first,  the  relation  of 
the  jaws.  This  is  determined  tentatively  at  the  time  the  l)ite  is  taken, 
concerning  which  it  was  said,  that  such  a  distance  sliould  be  estab- 
lished between  the  jaws  and  such  a  fulness  of  the  bite-plates  provided, 
that  the  lips  rest  in  contact  without  restraint  and  display  an  equal  amount 
of  mucous  membrane.  Although  the  contact  of  the  lips  in  the  manner 
described  as  desirable,  is  influenced  both  by  the  distance  between  the 
jaws  and  the  fulness  of  the  bite-plates,  these  two  factors  should  iiave 
been  so  adjusted  that  the  amount  of  protrusion  of  the  lips  desirable  in 
the  case  in  hand  is  obtained.     If  this  has  been  satisfactorilv  done  and 


RESTORATION  OF  FACIAL   EXPRESSION.  469 

(Iciituros  constructed  to  accord  with  the  forins  oi"  the  bite-pUites,  no  aUer- 
ation  in  tlie  (hstance  between  the  jaws  will  be  necessary. 

The  base  of  the  upper  hp,  in  rehition  with  the  nose  and  the  upper 
part  of  the  face,  is  fixeih  The  chin  and  tissues  up  to  a  point  opposite 
tiie  point  of  reflection  of  the  mucous  membrane  of  the  process  to  the 
k)wer  lip  are  also  fixed.  The  amount  of  outward  inclination  of  the  upper 
lip,  its  curve,  the  amount  of  mucous  membrane  displayed,  the  position 
of  the  lower  lip,  as  related  to  the  upper,  and  the  sulcus  mento-labialis  are 
the  factors  wdiich  may  be  adjusted.  The  thickness  of  the  lips  is  another 
factor  which  may  be  in  some  part  taken  as  an  index  of  their  position, 
thick  lips  beino;  usually  associated  with  an  outward  inclination  of  the 
teeth  and  a  projection  of  the  lips,  thin  lips  being  usually  associated 

Fio.  433 


„  __  j—   Linea  naso-labialis 

Philtrum   -^ =^== —  W 

Tutoereulum  -^ ^^^r~  ^ ^r      Angle  of  the  mouth 

^-,^^^--,—„^———,^       Sulcus  mento-labialis 
Mentum 


Full  face,  showing  good  contours  and  lines. 

with  a  less  prominent  position.  For  the  most  part  the  line  from  the  base 
of  the  nose  to  the  margin  of  the  mucous  membrane  of  the  upper  lip  is  ap- 
proximately a  straight  line.  It  is  curved  inward  where  the  margin  of 
the  lip  is  prominent,  the  curve  being  due  to  the  difference  in  thickness 
of  the  lip  at  this  point,  and  not  to  the  conformation  of  the  supporting 
structures  beneath.  Where  the  lower  jaw  occupies  a  distal  position, 
the  lip  may  be  either  in  a  vertical  line,  or  may  be  slightly  inclined  back- 
ward. 

The  sulcus  mento-labialis,  which  imparts  considerable  beauty  to  the 
form  of  the  lower  lip,  is  caused  by  the  greater  thickness  of  the  margin 
of  the  lower  lip,  by  the  contact  of  the  upper  anterior  teeth  with  its  upper 
surface  wdiich  serves  to  roll  it  slightly  outward,  and  by  the  intimacy  of 
attachment  of  the  skin  of  the  chin  to  the  mandible.  This  curve  is  to  be 
established,  if  possible,  but  where  great  absorption  of  the  fat  has  occurred. 


470 


SELECTION,   ARRANGEMENT,   AND   AUTTCULATTON. 


or  in  some  cases  from  an  orij^iiialdisj^osition  of  the  j)arts,  tliis  is  not 
possible. 

The  amount  of  nuicous  membrane  (Hsplayed  by  the  two  hps  should 
be  equal  in  cases  with  a  normal  relationship  of  the  jaws.  In  individuals 
with  a  retruded  lower  jaw  more  of  the  mucous  membrane  of  the  upper 
lip  will  be  displayed  than  of  the  lower.  Where  the  lower  jaw  is  pro- 
truded, there  is  likewise  a  corresponding  difference  in  amount  of  mem- 
brane visible. 

Viewing  the  face  from  the  front  the  follow^ing  points  are  to  be  noted: 
the  line  marking  the  point  of  contact  of  the  two  lips.  This  is  affected 
by  the  natural  configuration  of  the  lips,  by  the  distance  between  the 
jaws,  and  by  the  amount  of  projection  of  the  structures  supporting  the 


Fig.  434 


Continuous-gum  denture  showing  contours.      (Wilson.) 

lips  Unfortunately,  at  the  age  at  which  plate  dentures  are  necessary 
the  fine  lines  characteristic  of  youth  are  frecpiently  so  altered  that  the 
establishment  of  theselinesin their  mo.st beautiful  form  is  impossible. 
Of  course  the  original  condition  may  have  been  such  that  this  is  not 
possible.  The  ideal  cupid's  bow,  shown  in  Fig.  483  is  that  to  be  sought 
in  all  cases,  but  ordinarily  only  a  straight  line  of  separation  may  be 
obtained.  This  should  preferably  occupy  a  horizontal  plane  as  it 
does  usually  in  the  natural  condition,  although  cases  are  frequently 
seen  in  which  the  distal  ends  of  the  line  are  at  a  lower  level  than  the 
middle.  This  latter  condition  may  be  produced  if  the  jaws  have  been 
established  too  close  together.  Where  it  existed  originally,  of  course, 
no  improvement  can  be  made. 

The  philtrum  is  frequently  obliterated  by  the  falling  in  of  the  tissues 
after  the  loss  of  the  teeth,  if  age  has  not  already  had  this  effect.  The 
prosthetist,  probably,  has  no  influence  over  the  formation  of  this 
groove,  other  than  if  the  lips  are  put  upon  too  great  a  strain,  it  may  be 
further  obliterated.  The  same  may  be  said  of  a  prominent  tip  or 
tuberculum  of  the  upper  lip.  Both  age  and  the  loss  of  the  teeth  serve  to 
straighten  the  line  of  separation  between  the  lips  and  obliterate  this 


RESTORATION  OF  FACIAL  EXPRESSION.  471 

prominence,  while  in  those  cases  in  which  this  effect  has  not  ensued,  the 
tubercukira  should  be  preserved  by  imposing  no  great  strain  upon  the 
lips. 

The  canine  eminence  will  usually  require  considerable  restoration 
with  the  artificial  dentures,  because  of  the  large  amount  of  absorp- 
tion of  the  process  which  occurs  at  its  site.  The  temperamental  type 
of  the  individual  will  assist  in  affording  information  in  determining  the 
amount  of  building  to  be  undertaken  at  this  point.  Individuals  of  the 
bilious  temperament  and  its  various  combinations  will  require  promi- 
nentcanines  and  prominent  portions  of  the  plate  overljing  this  tooth. 
In  the  individual  case  reference  should  be  made  to  the  naso-labial 
fold,  which  is  usually  accentuated  both  by  age  and  the  loss  of  the  teeth. 
Ordinarily  it  extends  from  the  base  of  the  ala  of  the  nose  with  decreas- 

FiG.  435 


Wax  model  of  denture  with  extensive  contours. 

ing  depth  to  a  pomt  slightly  below  the  corner  of  the  mouth.  The  build- 
ing out  of  the  canine  eminence  will  increase  or  decrease  this  fold  by 
elevating  the  lips  to  the  level  of  the  cheek  tissue  adjoining  the  upper 
margin  of  the  fold.  In  determining  the  fulness  to  be  established  here, 
reference  should  also  be  made  to  the  already  established  inclination 
of  the  centre  of  the  lips.. 

In  instances  in  which  the  wrinkles  radiating  from  the  mouth  and 
caused  by  loss  of  the  teeth  have  been  of  long  standing  it  will  be  impos- 
sible to  eradicate  them  by  the  placing  of  the  denture.  Much  improve- 
ment will  occur  after  the  use  of  dentures  properly  restoring  the  contours, 
but  immediate  correction  of  the  defects  in  the  surface  of  the  skin  can- 
not be  expected.  This  is  also  true  of  the  groove  frequently  observed 
descending  from  the  angle  of  the  mouth  toward  the  chin,  but  the 
plates  should  remove  the.^e  wrinkles  as  far  as  possible. 


C  H  A  P  T  E  R     X  1 1 1. 

VULCANIZED  RUBBER  AS  A  BASE  FOR  ARTIFICIAL  DENTURES. 

By  CxEorge  H.  Wilson,  D.D.S. 
Vulcanite. — A  chemical  compound  of  Caoutchouc  and  Sulphur. 

CAOUTCHOUC. 

History, — Caoutchouc  is  a  native  Indian  name.  India-rubber  is  a 
name  given  the  material  because  its  early  use  in  Europe  was  to  remove 
black  lead  pencil  marks  from  paper.  Dr.  Priestley,  the  distinguished 
discoverer  of  oxygen,  mentions  this  use  in  a  publication  of  1770. 
Caoutchouc  must  have  been  known  in  America  at  a  very  early  period, 
l)ecause  balls  made  from  the  gum  of  a  tree,  lighter  and  bounding  better 
than  the  wind-balls  of  Castile,  are  mentioned  by  Herrera  when  speaking 
of  the  amusements  of  the  natives  of  Haiti,  in  his  account  of  the  second 
voyage  of  Columbus.  In  a  book  published  in  Madrid,  1G15,  Juan  de 
Torquemada  mentions  a  tree  which  yields  it  in  Mexico,  describes  the 
mode  of  collecting  the  gum,  and  states  that  it  Avas  made  into  shoes. 
More  exact  information  was  furnished  by  a  French  Academician,  who 
visited  South  America  in  1735.  While  the  Indians  used  it  more  than 
three  hundred  years  ago  for  water  bottles  and  gum  shoes,  it  was  only 
used  in  the  United  States  and  Europe  for  erasing  pencil  marks,  until 
about  1820,  when  it  was  applied  to  water-proofing  cloth.  As  caout- 
chouc became  hard  and  brittle  in  cold  weather  and  sticky  in  hot 
weather,  many  experiments  were  made  to  overcome  this  objectionable 
quality  which  resulted  in  the  discovery  of  vulcanite  in  1843. 

Physical  Properties.— Caoutchouc  is  the  dried  milky  juice  of  various 
trees  and  plants.  A  similar  gum  capable  of  vulcanization  can  be  ob- 
tained from  the  common  milk-weed  and  other  plants  of  temperate 
climates,  but  it  is  only  commercially  profitable  from  certain  trees  in  the 
tropics.  The  Brazilian,  or  Para  (a  shipping-port  on  the  Amazon  river) 
caoutchouc  is  the  product  of  several  species  of  Siphonia  (nat.  ord. 
Euphorbiacea^),  chiefly  Siphonia  elastica.  Bates  says  that  this  tree  is 
not  remarkable  in  appearance;  in  bark  and  foliage  it  is  not  unlike  the 
European  Ash,  but  the  trunk,  like  that  of  all  forest  trees,  shoots  up 
to  an  immense  height  before  throwing  off  branches.  The  India-rubber 
produced  in  New  Granada,  Ecuador  and  Central  America  is  obtained 
from  Castilloa  elastica  ;  that  of  East  India  from  the  beautiful  glossy- 
leaved  Ficus  elastica,  now  a  common  ornamental  plant  in  conserva- 
tories; that  of  Borneo  from  Urceola  elastica;  and  that  of  West  Africa 
from  several  species  of  Landolphia  and  also  Ficus. 
472 


CHEMISTRY  OF  CAOUTCHOUC.  473 

Afttn"  the  tr(H\s  arc  tapped,  tlie  juice  is  first  reeeivcl  in  clay  basins, 
and  then  is  solidified  in  various  ways — as  by  spreadino;  it  out  in  thin 
layers  and  evaporatino-  in  the  sun  or  by  the  aid  of  artificial  heat;  or  the 
emulsion  is  coagulated  by  the  leaves  of  a  kind  of  vine — a  method  used 
in  Central  America  which  gives,  however,  a  product  inferior  to  that  ob- 
tained by  evaporation.  The  evaporated  product  is  known  as  "biscuit." 
The  fresh  juice  has  the  consistency  of  cream,  is  yellow,  miscible  with 
water,  but  not  with  naphtha  or  other  solvents  of  ordinary  rubber;  its 
^specific  gravity  is  1.02 — 1.41;  the  yield  of  thegumis  aboutSO  percent. 
Pure  caoutchouc  is  devoid  of  odor  and  is  nearly  white;  it  has  the  specific 
gravity  of  .915.  The  finest  quality  of  caoutchouc  is  that  from  Brazil 
(Para)  which  has  the  least  impurities;  the  other  South  and  Central 
American  kinds  are  of  medium  quality;  East  India  rubber  ranks  next, 
while  the  African  rubber  is  quite  inferior. 

Commercial  India-rubber  is  a  dark,  tough,  fibrous  substance,  pos- 
sessing elastic  properties  in  the  highest  degree.  At  the  freezing  point  of 
water  it  hardens  and  largely  loses  its  elasticity.  The  gum  is  insoluble 
in  water  or  alcohol,  and  is  not  acted  upon  by  alkalies  or  acids  except 
when  the  latter  are  concentrated  and  heat  is  applied.  It  is  soluble  in 
ether,  chloroform,  bisulphide  of  carbon,  naphtha,  petroleum,  benzol, 
and  the  essential  oils,  and  in  many  of  the  fixed  oils  by  the  aid  of  heat. 
Caoutchouc  melts  at  a  temperature  of  250°  F.  and  does  not  again  re- 
sume its  former  elastic  state;  at  600°  F.  it  volatilizes  and  undergoes 
decomposition. 

Purifying. — In  the  manufacture  of  India-rubber  the  first  operation  is 
the  puritication  of  the  crude  material .  The  impure  rubber  is  cut  into 
minute  shreds  and  is  washed  by  powerful  machinery  immersed  in 
water,  which  releases  the  solid  impurities.  The  washed  gum  is  then 
placed  on  iron  trays  and  dried  in  a  room  lieated  by  steam.  The  material 
then  undergoes  a  process  of  kneading  under  very  heavy  rollers,  which 
causes  the  adhesion  of  its  various  pieces  to  each  other  and  ultimately 
yields  a  mass  or  block  of  India-rubber  so  compact  that  all  air-holes, 
other  cells  and  interstices  disappear. 

Chemistry  of  Caoutchouc/ — India-rubber,  as  is  well-known,  is  the 
product  of  the  coagulation  of  the  milky  juice  of  a  large  number  of  trees, 
creepers,  and  shrubs.  The  commercial  article  can  hardly  be  expected 
to  be  homogeneous,  and  still  less  a  pure  product  in  the  chemical  sense. 
Besides  accidental  impurities  of  sand  and  fragments,  it  contains  a 
greater  or  less  amount  of  oily  and  resinous  matter,  which  varies  greatly 
even  in  the  same  brand  of  rubber.  Para  rubber  contains  from  1  to  2 
per  cent. ;  Logus  rubber  from  3  to  7  per  cent. ;  Borneo  rubber  from  6 
to  21  per  cent.;  and  African  Flake  may  contain  as  high  as  64  per 
cent.  Lascelles-Scott  gives  the  composition  of  a  brand  of  unnamed 
origin : 

^  The  rnriter  uses  as  his  authority  for- this  paragraph  and  the  subsequent  ones  upon  the  Chemis- 
try of  Vulcanite,  "The  Chemistry  of  India-Rubber,"  by  Carl  Otto  Weber,  Ph.  D.,  published  by 
Charles  Griffin  and  Company,  Limited,  London.  J.  B.  Lippincott  Company,  Philadelphia,  1903. 


474  VULCANIZED  RUBBER  AS  A  BASE. 

India-rubber  (gum') .'{".13  per  cent. 

Albumen 2.71   per  cent. 

Resins .3 .  44  per  cent. 

Essential  oils Traces. 

Sugar 4. 17  per  cent. 

Mineral  matter 0 .  23  per  cent. 

Water 52.32  per  cent. 

The  pure  Para  gum  con.si.sts  of  soluble  and  insoluble  portions,  the 
latter  averaging  about  3.5  per  cent.  The  soluble  portion  has  a  formula 
of  C10H16  and  is  the  portion  with  which  the  sulphur  combines  to  form 
vulcanite.     The  formula  for  the  insoluble  portion  is  Ci^HcsOio. 

VULCANITE. 

History. — Charles  Goodyear^  of  New  Haven,  Conn.,  discovered  the 
process  of  curing  or  vulcanizing  India-rubber  in  1S43.  Thomas  Han- 
cock of  England  has  been  credited  with  making  this  discovery  contem- 
poraneously; but  his  own  writings  state  that  he  had  seen  small  sam- 
ples of  Goodyear's  work,  and  that  after  much  experimenting,  he  pro- 
duced the  same  thing;  so  the  priority  of  the  discovery  undoubtedly  be- 
longs to  Goodyear. 

C3n  January  30th,  1S44,  a  patent  was  granted  to  Charles  Goodyear, 
for  making  soft  or  flexible  rubber  that  would  resist  the  action  of  the 
usual  solvents  of  caoutchouc,  and  would  not  be  affected  by  cold  or  heat, 
if  the  temperature  were  not  raised  above  the  vulcanizing  point.  The 
mixture  he  preferred  was:  caoutchouc  25  parts,  sulphur  5  parts,  and 
white  lead  7  parts.     This  produced  soft  vulcanite. 

The  process  of  making  hard  rubber  was  patented  by  Nelson  Good- 
year, May  6,  1851.  His  formula  consisted  of  one-half  pound  of  sul- 
phur to  a  pound  of  caoutchouc  and  one-half  pound  of  any  one  of  a  long 
list  of  earthy  substances. 

A  patent  was  granted  to  Charles  Goodyear,  Jr.  "For  improvement 
in  plates  for  artificial  teeth,"  dated  March  4,1855.  He  says:  "The 
best  compound,  I  l)elieve  to  be  one  pound  of  India-rubber  or  gutta- 
percha (or  of  the  two  combined  in  suitable  proportions)  with  a  half 
pound  of  sulphur,  together  with  a  suitable  quantity  of  coloring  matter. 
To  obtain  a  suitable  color,  I  mix  with  caoutchouc  or  gutta-percha,  ver- 
milion, oxide  of  zinc,  oxide  of  iron,  of  any  coloring  substance  that  will 
stand  the  necessary  degree  of  heat  with  the  action  of  sulphur.  This 
compound,  after  having  been  molded,  is  subjected  to  heat  for  about 
six  hours,  and  in  so  doing,  I  gradually  raise  the  heat  to  about  230°  F., 
say  in  half  an  hour,  and  then  unless  there  be  a  considerable  quantity  of 
foreign  matter  present,  the  heat  may  be  raised,  quickly  as  may  be,  to 
about  295°  F. ;  otherwise,  I  raise  the  heat  more  slowly  and  keep  the 
compound  at  about  that  temperature  for  the  remainder  of  the  six  hours 
and  then  allow  the  whole  to  cool  down,  when  the  process  will  be  com- 
pleted." 

'This  historical  sketch  of  vulcanite  is  made  up  largely  from  the  Monograph,  "Instructions  in 
Vulcanite"  by  Prof.  E.  WUdman,  M.D.,  D.D.S.     PhUadelphia:  Samuel  S.  White,  1867. 


COMPOSITION  OF  VULCANITE  FOR  ARTIFICIAL  DENTURES.     475 

A  patent  was  granted  in  June,  1857,  to  H.  H.  Day  for  vulcanizing 
very  thick  pieces  of  rubber.  To  accomplish  this,  he  mixes  with  the 
matter  prepared  for  vulcanization,  a  substance  that  will  prevent  its 
becoming  spongy  or  cellular,  by  absorbing  the  sulphur  gases  as  fast  as 
generated.  The  material  which  he  proposed  to  employ  for  this  pur- 
pose, is  ordinary  fire  clay,  but  other  substances  capable  of  absorbing 
the  gas  may  be  employed. 

In  Austin  G.  Day's  specification  we  find  some  interesting  remarks 
upon  the  nature  of  rubber  compounds.  In  contra-distinction  to  Nelson 
Goodyear's  hard  and  inflexible  substance,  he  claims  his  compound  to 
be  a  hard,  but  highly  elastic  material  obtained  by  a  process  differing 
from  that  of  N.  Goodyear's  in  the  length  of  time,  in  the  degree  of  heat, 
in  the  proportion  of  the  ingredients,  and  in  the  mode  of  equalizing  the 
temperature.  Day's  composition  is  one  pound  of  purified  Para  rubber 
and  one-half  pound  of  sulphur. 

He  remarks :  "In  the  vulcanizing  process,  there  is  eliminated  during 
the  whole  operationa  constant  discharge  of  sulphurettedhydrogenand 
other  sulphuretted  gases,  which  must  have  means  of  escape  through  the 
pores  of  the  mass  while  being  vulcanized.  By  my  present  improved 
management  of  the  heat  in  vulcanizing,  by  raising  it  very  gradually, 
step  by  step,  to  the  highest  point,  I  am  enabled  to  vulcanize  pieces  of 
an  inch  or  more  in  thickness  with  great  uniformity  and  perfection.  A 
mixture  containing  earthy  matter  may  be  vulcanized  in  much  shorter 
time  than  one  consisting  of  caoutchouc  and  sulphur  alone,  and  yet  be 
solid,  owing  to  the  earthy  matter  facilitating  the  escape  of  the  gases 
generated  in  its  substance  during  the  process.  At  the  same  time  such 
compositions  are  destitute  of  elasticity  and  flexibility.  For  a  piece 
five-eights  of  an  inch  thick,  the  time  required  for  vulcanizing  is  thirteen 
and  a  half  hours : 

It  is  held  at 275°  F.,  for  6  hrs. 

Then  raised  to  and  held  at ■ £S0°  F..  for  3  hrs. 

Then  raised  to  and  held  at £90°  F.,  for  2  hrs. 

Then  raised  to   and  held  at    295°  F.,  for  2  hrs. 

Then  raised  to   and  held  at .300°  F..    for  }^   hr. 

Composition  of  Vulcanite  for  Artificial  Dentures — -As  the  formulae 
of  the  various  makes  of  rubber  are  "trade  secrets"  of  the  manufac- 
turers, our  knowledge  is  limited  to  the  general  specifications  of  patent 
papers  and  the  writings  which  detail  the  experiments  of  Prof.  Wildman 
and  others. 

Both  the  soft  pliable  and  the  hard  flexible  vulcanite  are  used  in  the 
construction  of  dentures.  The  essential  components  of  vulcanite  are 
caoutchouc  and  sulphur,  the  ratio  varying  according  to  the  use  for 
which  the  product  is  designed.  All  other  ingredients  are  for  coloring 
or  to  cheapen  the  product.  The  soft  pliable  variety  used  in  dentistry  is 
known  as  velum  rubber,  because  its  most  important  use  is  for  vela  for 
cleft  palates.  It  contains  sulphur  to  the  extent  of  about  one-fifth  of  the 
weight  of  the  gum.  Hard  vulcanite,  sometimes  called  ebonite,  con- 
tains by  weight  one-half  as  much  sulphur  as  caoutchouc. 


476  VULCANIZED   RUBBKIl   AS  A    BASE. 

Some  of  the  fonniilas  jrivon  by  Prof.  Wildman  arc: 

DARK  BROWN.  CiRAYISH  WHITE 

Caoutchouc 48  parts  Caoutchouc 48  parts 

Sulphur ; 24       "  Sulphur 24     " 

White  Oxide  ZiiFc .96      " 

RED.  BLACK. 

Caoutchouc. 48  parts  Caoutchouc 48    parts 

Sulphur 24     "  Sulphur 24     " 

Vermilion 36     "  Ivory-black  or 

Drop-black 24     " 

DARK  PINK.  JET  BLACK. 

Caoutchouc. 48  parts  Caoutchouc 48  parts 

Sulphur 24     "  Sulphur i;4     " 

White  Oxide  of  Zinc 30     "  Ivorv-black) 

or  ) 48     " 

Vermilion 10     "  Drop-black 

If  pure  caoutchouc  is  burned,  there  should  be  but  about  three  per 
cent,  of  dark  ash  remaining.  Sulphur  and  vermilion  (mercuric  sulphide) 
leave  no  ash,  hence  the  per  centum  of  ash  from  rubber  containing  these 
materials  should  be  less  than  three  per  cent,  in  the  ratio  of  the  amount 
of  these  materials  to  the  caoutchouc.  Some  rubbers  leave  as  hicrh  as 
sixty  per  cent,  of  ash.  It  would  be  reasonable  to  suppose  that  the 
strength  would  be  reduced  in  ratio  to  the  amount  of  the  ash,  but  this  is 
not  true,  as  the  pure  gumandsulphur  produce  the  strongest  vulcanite; 
the  red  and  black  are  nearly  the  same  strength,  although  the  black 
rubber  will  leave  a  much  larger  ash  than  red,  because  the  coloring 
matter  is  animal  charcoal  composed  largely  of  phosphate  and  carbonate 
of  lime,  while  the  mercuric  sulphide  would  be  entirely  volatilized.  The 
oxide  of  zinc  and  other  earthy  matter  in  the  pink  and  white  rubbers 
have  a  very  deleterious  effect  upon  the  flexibility  and  tenacity  of 
the  vulcanized  rubber,  so  much  in  fact,  that  these  light  colored  vul- 
canites are  not  one-fourth  as  strong  as  the  brown,  red  or  black. 

Physical  Properties  of  Vulcanite — Vulcanite  is  hard,  flexible,  and 
horn-like  in  texture.  Dr.  George  B.  Snow  gives  the  specific  gravity  of 
a  specimen  of  black  vulcanite  as  1.1 974;  and  that  of  the  same  piece  before 
vulcanizing  as  1 .1333.  The  specific  gravity  varies,  as  it  is  much  aft'ected 
by  the  coloring  matter,  and  is  also  increased  by  the  temperature 
and  time  of  vulcanization.  Caoutchouc  expands  upon  heating. 
Dr.  Snow  says :  "Rubber  expands  by  heat  more  rapidly  than  any  other 
solid  body.  Its  rate  of  expansion  at  ordinary  temperatures,  from  70° 
to  90°  F.  is  over  six  times  that  of  iron,  about  five  times  that  of  brass, 
and  nearly  four  times  that  of  zinc  which  is  the  most  susceptible  to  ex- 
pansion by  heat  of  any  of  the  metals.  Its  rate  of  expansion  is  known 
to  increase  as  the  temperature  rises,  but  it  has  not  been  definitely  deter- 
mined." In  vulcanizing  soon  after  chemical  action  begins  (24S°  F.), 
expansion  ceases  and  contraction  commences,  the  latter  being  much 
affected  by  the  contained  foreign  matter,  by  a  high  or  low  temperature, 
and  by  a  long  or  short  time  of  vulcanization.  Its  increased  specific 
gravity  is  due  to  this  contraction. 

The  usual  solvents  of  caoutchouc  have  but  little  action  upon  vulcan- 


CHEMISTRY  OF  VULCANIZATION.  477 

ite,  and  no  agent  which  can  be  tolerated  in  the  mouth  has  any  action 
upon  it.  It  is  susceptible  of  a  high  polish.  It  is  very  opaque,  and, 
therefore,  does  not  imitate  well  the  appearance  of  the  mucous  mem- 
brane. It  is  a  very  poor  conductor  of  thermal  and  electrical  changes, 
in  consequence  of  which  it  is  not  conducive  to  the  health  of  the  tissues 
upon  which  it  is  worn.  It  is  porous,  although  this  condition  is  invis- 
ible to  the  eye.  It  absorbs  the  secretions  of  the  mouth,  even  though 
the  rubber  has  been  perfectly  vulcanized,  and  when  improperly  vul- 
canized, it  becomes  so  saturated  with  decomposing  secretions  that  it 
is  exceedingly  offensive.  Great  care  should  be  used  in  vulcanizing 
rubber  that  is  to  be  worn  in  the  mouth,  and  the  patient  should  be 
thoroughly  instructed  in  cleansing  it. 

New  rubber  can  be  added  to  old  vulcanite  by  reheating;  hence  vul- 
canite dentures  can  be  easily  repaired.  It  is  unnecessary  to  add  a 
solution  of  rubber  to  vulcanite  to  aid  in  its  repair,  as  the  solvent  has  no 
action  upon  the  vulcanite,  only  leaving  a  thin  layer  of  soft  rubber  to 
penetrate  the  pores  of  the  vulcanite,  a  result  better  accomplished  by  heat 
and  pressure. 

Chemistry  of  Vulcanization. — Vulcanization  consists  of  the  chemical 
union  of  caoutchouc  and  sulphur,  probably  producing  a  series  of  com- 
pounds having  the  formula  CioHigSo  for  the  highest  combination,  and 
C100H160S  for  the  lowest,  with  a  series  from  the  lowest  to  the  highest. 

V^ilcanization  can  be  brought  about  either  by  the  cold  or  the  hot  pro- 
cess, and  by  using  with  the  latter  either  the  dry  or  the  wet  method.  The 
essential  requisite  is  to  secure  the  union  of  the  sulphur  with  the  poly- 
prene  (CioHir,)- 

The  cold  process  is  by  the  use  of  sulphur  monochloride  and  is  only 
suitable  for  very  thin  layers  of  rubber,  being,  therefore  not  applica- 
ble for  dental  use.  An  attempt  has  been  made  to  sell  to  the  profes- 
sion office  rights  for  the  use  of  a  porcelain  enamel  for  facing  vulcanite 
dentures.  This  method  was  based  upon  the  cold  vulcanization  pro- 
cess. While  the  results  were  an  improvement  upon  ordinary  pink  rub- 
ber, the  product  lacked  the  translucent  effect  of  fused  porcelain,  its 
durability  was  uncertain,  and  the  process  was  long  and  tedious. 

Mr.  Weber  in  the  work  previously  referred  to,  says:  "We  turn  our  at- 
tention first  to  the  question  of  the  general  action  of  sulphur  upon  India- 
rubber  at  high  temperatures.  The  sulphur  bath  method  might  appear 
from  several  points  of  view  the  most  suitable  method  of  studying  this 
question,  but  after  a  number  of  attempts,  I  abandoned  it  in  favor  of 
the  method  of  subjecting  carefully  prepared  homogeneous  mixtures  of 
Para  rubber  with  a  definite  amount  of  sulphur,  to  the  action  of  heat. 
Again  in  this  case  we  have  the  choice  of  several  methods  of  heating,  but 
the  one  of  heating  pieces  of  Para  mixture  of  uniform  thickness  to  vul- 
canizing temperatures  when  immersed  in  water,  appeared  to  me  the 
most  satisfactory,  as  it  involves  the  minimum  of  loss  of  sulphur  by  evap- 
oration. 

"The  experiments  were  carried  on  with  strips  cut  from  a  calendered 
sheet  3  mm.  in  thickness — a  mixture  of  100  parts  of  Para  rubber  witli 


478  VULCANIZED   RUBBER   AS  A    BASE. 

ten  parts  of  pure  precipitated  sulphur.  These  strips  were  vulcanized  in 
a  phosphor-bronze  digestor. 

"The  digestor  is  provided  with  a  thermometer  tube  (thermometer  in 
mercury),  a  pressure  gauge,  and  a  blow-oft"  valve.  In  the  digestor  a 
porcelain  beaker  is  suspended  so  that  it  is  clear  of  the  bottom.  The 
dig.estor  is  filled  to  about  one-([uarter  of  its  capacity  with  water;  the 
beaker  is  completely  charged  with  water,  and  a  number  of  the  strips  to 
be  experimented  upon,  immersed  in  it.  The  digestor  is  then  closed, 
rapidly  heated  to  the  retjuired  temperature,  and  maintained  thereat, 
either  by  carefully  adjusting  the  gas  burner,  or  by  means  of  some  form 
of  thermo-regulator.  At  regular  intervals  one  of  the  strips  is  withdrawn 
after  blowing  off  steam  and  rapidly  opening  the  digestor,  which  is  then 
immediately  closed  again  to  continue  the  series.  The  time  error  caused 
by  these  successive  withdrawals  does  not  exceed  four  minutes  per  sam- 
ple. Of  course  the  water  lost  by  the  blow-off  steam  is  from  time  to 
time  made  up  with  boiling  water. 

"The  strips  thus  withdrawn  are  marked,  and  subsequently  cut  into 
very  fine  threads,  which  are  freed  from  every  trace  of  uncombined  sul- 
phur by  extraction  with  acetone  in  a  Soxhlet  extractor.  The  greatest 
care  was  employed  to  render  this  operation  perfect,  every  sample  being 
subjected  to  a  three  days'  continuous  extraction.  The  extracted  sam- 
ples were  dried  in  a  current  of  carbonic  acid  in  the  water  oven,  and, 
until  analysis,  were  preserved  in  carefully  stoppered  glass  tubes. 

"About  one  gram  of  each  of  these  samples  was  used  for  analysis. 
The  sulphur  determinations  were  all,  without  exception,  carried  out  by 
Carius'  method,  as  the  results  by  the  much  simpler  and  more  expedi- 
tious inethod  proposed  by  Henriques,  were  found  to  be  liable  to  an 
error  approaching  0.1  per  cent,  in  magnitude.  In  this  manner  the 
following  results  were  obtained: — 

VnLCANIZATION    OF   PaRA    RUBBER. 


Duration  of 

Temperature  of  Vul 

canization. 

Vulcanization, 

120°  C. 

125°  C. 

130°  C. 

135°  C. 

140°  C. 

s.% 

S.% 

S.% 

S.% 

S.% 

30  mins. 

0.71 

0.71 

0.99 

1.76 



00     „ 

1.18 

1.32 

1.44 

2.17 



90     „ 

1.31 

1.67 

2.04 

2.36 



120     „ 

1.62 

1.91 

2.32 

3.92 

5.07 

150     „ 







4.02 



180     „ 

1.78 

2.11 

2.94 

4.18 

6.05 

240     „ 

1.93 

2.22 

5.00 

5.50 



300     „ 

2.25 

2.35 

5.27 

6.74 



360     „ 

2.60 

3.80 

5.82 

6.88 



420     „ 

3.71 

4.04 

6.04 

6.97 



480 

3.94 

4.31 

6.33 

7.13 



"These  figures  amply  suffice  to  demonstrate  indisputably  the  fact,  even 
quite  recently  again  denied,  that  the  vulcanization  of  India-rubber  with 
sulphur  involves  the  chemical  combination  of  these  two  substances,  at 
any  rate  as  far  as  the  vulcanization  of  Para  rubber  is  concerned. 

"  That  dift'erent  brands  of  India-rubber  behave  very  difterently  in 
the  vulcanization  process,  is  a  well-known  fact,  but  what  we  know  at 


CHEMISTRY  OF  VULCANIZATION.  479 

this  moment  respecting  the  composition  and  chemical  relationship  of 
these  different  brands  entitles  us  to  assume  that,  although  their  be- 
havior untler  vulcanization  may  not  be  identical  v/ith  the  Para  rubber, 
it  will  be  more  or  less  closely  analogous  to  it." 

Following  this,  Mr.  Weber  gives  a  tabulation  of  his  experiments 
with  Upper  Congo,  Beni  River,  Ceara  and  Borneo  rubber  for  the  same 
duration  of  vulcanization  and  for  125°  C.  and  135°  C.  He  then  sums 
up  these  experiments  thus: 

,  "The  extremely  interesting  results  here  tabulated  remove  all  doubt 
that  the  vulcanization  of  India-rubber  is  a  chemical  process  resulting 
in  the  formation  of  a  polyprene  sulphide.  The  rate  at  which  the  sulphur 
enters  into  combination  with  the  India-rubber  hydrocarbon  (polyprene) 
is  characteristic  for  each  brand  of  India-rubber.  Some  of  the  above 
series  were  repeatedly  investigated,  always  with  the  same  result. 

"There  arises  now,  of  course,  at  once  the  question  as  to  the  nature  of 
the  process  by  which  sulphur  enters  into  combination  with  the  polyprene, 
whether  the  polyprene  sulphide  or  sulphides  formed  are  addition  or  sub- 
stitution products.  Certainly  what  we  already  know  respecting  the 
chemical  nature  of  India-rubber,  leads  us  to  infer  that  the  vulcaniza- 
tion process  consists  essentially  in  the  formation  of  an  addition  product 
of  sulphur  and  polyprene.  This  assumption,  however,  requires  support 
in  view  of  the  fact  that  quite  a  number  of  writers,  from  Payen  to  most 
of  the  recent  authors,  declare  that  vulzanization  is  accompanied  by  the 
evolution  of  hydrogen  sulphide,  thereby  implying  that  the  process  is  a 
substitution,  and  not  an  addition  process.  Indeed,  most  of  the  recent 
authors  on  this  subject  state  this  in  so  many  words.  We  shall  therefore 
have  to  subject  this  point  to  a  careful  examination. 

"Assuming  the  compound  of  polyprene  and  sulphur,  which  indisput- 
ably forms  in  the  vulcanization  process,  to  be  a  substitution  product,  it 
follows  with  absolute  necessity  that  for  each  32  parts  of  sulphur  combin- 
ing with  the  polyprene,  we  must  obtain  34  parts  of  hydrogen  sulphide. 
Now,  in  the  process  of  vulcanization  as  practically  carried  out,  we  ob- 
tain on  an  average,  a  product  containing,  say,  2.5  per  cent,  of  combined 
sulphur.  Consequently  the  vulcanization  of  one  ton  of  India-rubber,  on 
the  above  assumption,  would  be  bound  to  yield  very  nearly  60  pounds 
of  hydrogen  sulphide,  or  approximately  18,000  litres.  Considering  that 
in  a  number  of  factories  the  amount  of  India-rubber  vulcanized  daily 
largely  exceeds  one  ton  in  weight,  we  should  expect  to  find  the  vulcani- 
zing rooms  of  these  factories  reeking  with  gas.  As  a  matter  of  fact,  how- 
ever, there  is  scarcely  ever  a  trace  of  this  gas  to  be  discovered  in  the 
rubber  works'  atmosphere,  and  the  very  rare  cases  in  which  its  pres- 
ence becomes  noticeable  may  always  be  considered  as  an  indication 
of  something  having  gone  wrong. 

"In  the  vulcanization  of  'hard  rubber'  goods  (ebonite  vulcanite) 
faint  but  distinct  traces  of  hydrogen  sulphide  are  generally,  perhaps 
always  observable,  but  they  could  not  be  ascribed  to  the  vulcanization 
process  proper — the  combination  of  polyprene  with  sulphm- — which 
process,  if  it  consisted  in  the  substitution  of  hydrogen  for  sulphur,  should 


480  VULCANIZED  RUBBER  AS  A    BASE. 

ciiiisc  a  perfectly  torrential  evolution  of  hydrogen  sulphide,  seeing  that 
'  hard  rubber'  contains  at  least  20  per  cent,  of  combined  sulphur. 

"It  is,  therefore,  certain  that  if  hydrogen  sulphide  forms  at  all  in  the 
vulcani/.ini,'  process,  its  amount  is  ^utterly  inadequate  to  support  the 
assumption  that  the  process  of  vulcanization  is  a  substitution  process 

"J^aboratory  experiments  on  this  question  lead  to  exactly  the  same 
conclusion.  If  the  experiments  are  carried- out  with  technically  pure 
Para  rubber  under  conditions  absolutely  precluding  the  escape  of  any 
gaseous  j)ro(luct  of  the  reaction,  very  minute  traces  of  hydrogen  sulphide 
may  sometimes  be  observed,  l)ut  in  a  considerable  number  of  carefully 
devised  experiments  with  highly  purified  Para  rubber,  no  hydrogen 
sulphide  at  all  could  be  detected. 

"If,  on  the  other  hand,  the  'insoluble'  part  of  India-rubber  is  mixed 
withsul])hur,  and  this  mixture  is  subjected  to  a  vulcanizing  temperature 
say,  about  13o°C. — a  considerable  evolution  of  hydrogen  sulphide  takes 
place,  due  to  the  formation  of  a  substitution  product  of  this  insoluble 
body,  CjuIifijjOio,  with  sulphur.  This  substitution  process  certainly  pro- 
ceeds much  slower  than  the  vulcanization  process  of  India-rubber 
(polyprene).  Under  the  same  conditions  of  temperature  and  the  time 
under  which  polyprene  forms  a  vulcanization  product  containing  4 
per  cent,  of  sulphur,  the  above  named  insoluble  constituent  forms  a 
s'jbtitution  product  containing  at  most  0.7  per  cent,  of  sulphur. 

"From  these  facts  we  are  justified  in  drawing  the  following  conclu- 
sions: 

"1.  The  India-rubber  hydrocarbon,  polyprene  CioHie,  combines 
with  sulphur  without  evolution  of  hydrogen  sulphide.  The  vulcaniza- 
tion process  of  India-rubber  is,  therefore,  an  addition  process. 

"2.  The  insoluble  constituent  of  India-rubber,  which  forms  only 
an  insignificant  proportion  of  the  technical  product,  not  exceeding  five 
per  cent,  of  the  total,  combines  with  sulphur  under  vulcanizing  condi- 
tions at  a  very  slow  rate  with  evolution  of  hydrogen  sulphide  and  with 
the  formation  of  a  substitution  product. 

"The  above  conclusively  settles  the  question  regarding  the  general 
chemical  aspect  of  the  vulcanization  process,  but  it  confronts  us  with 
the  further  question  respecting  the  quantity  of  sulphur  combining  with 
India-rubber  in  this  process,  as  well  as  the  more  intimate  structure  of 
the  compound  thus  formed." 

Interesting  and  instructive  as  the  work  of  Mr.  Weber  is,  the  limits  of 
this  chapter  will  not  permit  us  to  follow  him  in  detail,  but  only  to  give 
his  conclusions. 

"The  process  of  vulcanization  consists  in  the  formation  of  a  contin- 
uous series  of  addition  products  of  polyprene  and  sulphur,  with  prob- 
ably a  polyprene  sulphide  CiooHimS,  as  the  lower,  and  CiooHieoSzo  as  the 
upper  limit  of  the  series.  Physically  this  series  is  characterized  by 
the  decrease  of  distensibility,  and  the  increase  of  rigidity,  from  the 
lower  to  the  upper  limit.  Which  term  of  the  above  series,  that  is, 
which  degree  of  vulcanization  is  produced,  is  in  every  case  only  a  func- 
tion of  temperature,  time,  and  the  proportion  of  sulphur  present. 

"As  a  chemical  reaction  the  vulcanization  process  is  not  influenced  by 


CONSTRUCTION  OF   VULCANITE  VENTURES.  481 

the  physical  state  of  the  India-rubber  colloid ;  but  the  physical  state  of 
the  India-rubber  colloid,  while  under  vulcanization  largely  determines 
the  physical  constants  of  the  vulcanization  product." 

From  the  above  we  conclude  that  dental  vulcanite  is  essentially 
polyprene  disulphide  having  the  symbol  CioHjoS.  which  contains  32 
per  cent,  of  combined  sulphur. 

ADVANTAGES  AND  DISADVANTAGES  OP  VULCANITE  AS 
A  BASE  FOR  ARTIFICIAL  DENTURES. 

Advantages. — First: — It  is  easy  of  manipulation;  it  can  be  molded 
into  any  form,  and  it  becomes,  upon  proper  vulcanization,  very  strong 
tough  and  flexible.     It  is  repaired  with  equal  ease. 

Second: — It  is  the  lightest  of  all  substances  used  in  the  mouth;  its 
specific  gravity  is  from  1.15  to  1.50,  while  aluminum,  the  lightest  metal 
suitable  for  use  in  the  mouth,  has  a  specific  gravity  of  from  2.5  to  2.7. 

Third: — It  is  inexpensive,  both  as  to  cost  of  material  and  labor  in 
construction,  thus  bringing  it  within  the  reach  of  patients  unable  to 
afford  metal  plates. 

Fourth: — There  is  no  material  with  which  contours  can  be  so  easily 
and  perfectly  restored. 

Disadvantages. — First: — It  is  a  very  poor  conductor.  It  prevents 
the  proper  radiation  of  heat  from  the  mucous  membrane  over  which  it 
is  placed,  thereby  leading  to  excessive  resorption  of  the  hard  tissue  and 
lowering  the  vitality  of  the  soft  tissue,  in  consequence  of  which  they 
are  more  subject  to  the  action  of  irritants. 

Second: — Because  it  is  a  porous  material  and  because  this  condition  is 
greatly  exaggerated  by  improper  vulcanization,  it  affords  lodgment  for 
bacteria,  the  products  of  which  are  very  strong  irritants  to  the  soft 
tissue. 

The  physical  phenomena  of  expansion  and  contraction  in  the  vul- 
canization process  are  by  some  considered  as  disadvantages,  but  these 
can  be  so  well  controlled  by  modern  methods  of  manipulation,  that  they 
should  not  be  considered. 

Red  and  pink  rubber  are  by  many  considered  injurious  because  of 
the  coloring  matter,  vermilion  (mercuric  sulphide).  This  criticism  is 
unjust  because  pure  mercuric  sulphide  is  insoluble  in  water,  alcohol, 
alkali,  and  all  acids,  (except  nitro-hydrochloric  acid),  which  under  no 
condition  should  come  in  contact  with  red  or  pink  vulcanite,  as  this 
acid  converts  HgS  into  HgCL  (corrosive  sublimate). 

Only  high  grades  of  rubber  should  be  used  in  the  mouth  as  the 
cheap  grades  may  contain  injurious  impurities. 

CONSTRUCTION  OF  VULCANITE  DENTURES. 

The  history  and  the  physical  and  chemical  properties  of  caoutchouc 
and  vulcanite  have  been  treated  at  considerable  length,  under  the  belief 
that  ^ith  this  information  fully  set  forth,  the  student  will  pursue  the 

31 


^ 


482  VUl.CAMZKl)   RUBBER  AS  A    BASE. 

stiuly  of  the  techiii(|ue  of  the  construction  of  vulcanite  dentures  more 
intelHgently  and  with  more  interest  and  profit. 

It  is  important  in  dental  technique  that  every  step  in  the  series  of  an 
operation  be  carefully  and  accurately  performed,  otherwise  the  desired 
results  cannot  be  obtained. 

There  are  two  general  methods  of  constructing  vulcanite  dentures, 
which  we  shall  name  the  Double  Vulcanization  Method  and  the  Single 
Vulcanization  Method.  The  first  method  is  best  adapted  to  all  full 
cases  where  contour  restoration  of  the  gum  tissue  is  re(juired;  also  to 
some  partial  cases.  The  second  method  is  best  adapted  to  full  cases 
where  little  or  no  gum  restoration  is  required  and  to  the  larger  portion 
of  partial  cases. 

FULL  UPPER:  DOUBLE  VULCANIZATION  METHOD. 

The  operation  consists  of  taking  the  impression,  making  the  cast, 
forming  a  base-plate,  and  finishing  the  maxillary  surface  thereof;  of 
obtaining  the  occlusion  models,  arranging  the  teeth  and  proving  the 
contour  and  expression;  of  preparing  the  case  for  flasking,  packing, 
vulcanizing,  and  finishing. 

Impressions. — It  is  imperative  in  vulcanite  work  that  a  perfect  plas- 
ter impression  be  obtained.  The  technique  of  this  operation  is  described 
in  Chapter  VII. 

The  Cast. — Because  of  the  heavy  pressure  to  which  the  cast  will  be 
subjected  in  molding  the  rubber,  it  should  be  made  of  a  material  that 
cannot  be  compressed.  The  Spence  plaster  compound  is  the  best  for 
this  work.  It  is  better  practice  in  vulcanite  work  to  carve  and 
make  additions  to  the  cast  for  equalizing  the  pressure  of  the  den- 
ture than  to  alter  the  impression.  The  carN'ing  can  be  done  as 
described  in  the  chapter  on  this  subject.  Obviously,  additions  to 
the  cast  must  be  made  of  a  material  that  will  stand  the  heat  of  the 
vulcanizer.  Tin  is  best  for  this  purpose  as  it  does  not  discolor  the 
rubber.  Number  60  tin-foil,  which  is  about  .005  of  an  inch  thick,  is 
well  adapted  for  this  use,  and  can  be  applied  in  one  or  more  thicknesses 
by  attaching  each  layer  with  sandarac  varnish.  Thicker  pieces  of  tin 
can  be  made  by  rolling  out  bar  tin,  after  which  they  are  annealed  by 
placing  a  few  moments  in  boiling  water.  This  tin  plate  is  fastened  to 
the  cast  by  one-eighth  inch  tacks  or  brads,  or  is  retained  by  the  tin 
foil  used  for  finishing  the  maxillary  surface. 

The  Base-plate. — The  cast  having  been  properly  prepared,  the  base- 
plate is  made  by  warming  and  evenly  forming  a  sheet  of  thin  base- 
plate wax  over  the  cast.  With  a  warm  wax  spatula  the  excess  wax  is 
cut  off,  permitting  the  wax  pattern  to  extend  one-sixteenth  of  an  inch 
farther  over  the  sides  of  the  cast  than  it  is  desired  to  have  the  plate 
extend  when  it  is  finished.  The  hot  spatula  is  then  passed  around 
the  edge  of  the  wax  which  causes  it  to  adhere  to  the  cast.  The  cast 
with  the  wax  base-plate  is  now  flasked  in  a  Star  or  Wilson  flask. 
(Figs.  462  and  463.) 

Flasking  the  Base-plate. — The  flasking  is  done  with  regular  dental 


THE  SILEX  METHOD.  483 

plaster,  and  should  be  so  arranged  that  the  separation  of  the  two  por- 
tions will  be  at  the  periphery  of  the  wax.  The  plaster  in  the  first  section 
of  the  flask  must  be  coated  with  a  separating  fluid.  Any  of  the  various 
liquids  used  for  separating  plaster,  may  be  used,  except  oil  which  should 
never  be  used  in  rubber  work,  as  it  has  a  deleterious  efi^ect  upon  the 
vulcanizing  rubber.  After  the  flask  is  filled,  it  should  stand  until  the 
plaster  is  thoroughly  hard.  French's  regular  dental  plaster  will  re- 
quire not  less  than  twenty  minutes  and  the  slower-setting  plasters  from 
thirty  to  forty-five  minutes.  The  flask  is  now  placed  in  a  stew  pan  or 
any  convenient  receptacle  and  is  covered  with  cold  water.  The  water 
is  heated  to  ebullition,  when  the  flask  is  removed  from  the  water  and 
separated.  The  wax  will  be  sufiiciently  softened  to  permit  of  easy  re- 
moval. It  is  desirable  to  have  all  wax  removed  without  melting,  but 
should  a  portion  of  the  wax  be  melted  upon  the  cast  it  should  be  washed 
away  with  boiling  water.  Some  experience  will  be  required  to  know 
when  to  take  the  flask  from  the  water.  Large  cases  in  which  the  wax 
is  very  near  the  sides  of  the  flask  may  require  opening  just  before  the 
water  reaches  the  boiling  point;  while  small  cases  in  which  the  wax 
is  much  nearer  the  centre  of  the  flask  may  require  boiling  for  a  minute 
or  two. 

An  excess  space  to  receive  the  superfluous  rubber  should  be  cut  in 
the  cast  portion  of  the  flask,  beginning  one-eighth  of  an  inch  from  the 
mold  and  extending  to  the  rim  of  the  flask.  Small  grooves  or  gate- 
ways are  cut  from  the  mold  to  this  excess  space.     (Fig.  446.) 

Finishing  the  Maxillary  Surface  of  the  Base-plate. — The  surface 
of  the  cast  should  now  be  coated  with  a  material  that  will  give  a  hard  and 
smooth  finish  to  the  maxillary  surface  of  the  vulcanite.  There  are 
two  general  methods,  which  are  known  as  the  tin,  and  the  liquid-silex 
methods. 

The  Tin  Method. — This  method  is  preferable  as  it  gives  a  smoother 
and  denser  surface  to  the  vulcanite,  especially  if  any  wax  has  been 
melted  into  the  cast.  A  sheet  of  No.  6  or  No.  10  tin-foil  is  nicely  fitted 
over  the  cast  with  the  thumb  and  finger.  It  is  then  removed  and  the 
excess  of  tin  cut  away  with  sharp  scissors,  as  indicated  by  the  imprint 
of  the  edge  of  the  cast  upon  the  tin.  The  cast  is  now  coated  with  san- 
darac  varnish,  and  the  tin  is  at  once  replaced,  and  firmly  pressed  and 
gently  rubbed  with  a  wad  of  soft  tissue  paper  until  there  is  perfect 
adaptation  to  the  cast.  The  tin  should  be  rubbed  until  it  has  a  well 
burnished  surface.  It  is  important  that  the  tinned  cast  be  coated  with 
a  lather  of  soap.  This  is  accomplished  by  wetting  a  soft  bristle  brush 
and  rubbing  it  upon  a  cake  of  soap  and  then  upon  the  palm  of  the  hand, 
until  a  smooth  lather  is  formed,  which  is  appHed  to  the  tinned  surface; 
or  a  thin  w^ash  of  Johnson's  ethereal  soap  may  be  used.  If  the  soap  is 
not  applied,  the  tin  and  vulcanite  will  adhere  very  strongly  and  can  only 
be  separated  by  dissolving  the  tin  with  mercury  or  hydrochloric  acid. 

The  Silex  Method. — The  liquid-silex  method  has  the  advantage  of 
being  more  easily  applied,  and  if  the  surface  of  the  cast  is  entirely  free 
of  wax  or  oily  substances,  it  will  give  nearly  as  good  results.  A  clean  ox- 
hair  or  camels-hair  brush  is  dipped  into  the  liquid-silex  and  is  then  ap- 


484  VULCANIZED  RUBBER  AS  A   BASE. 

plied  to  the  cast.  It  will  be  necessary  to  occasionally  dip  the  brush  into 
water,  so  that  tlie  silex  may  be  well  diluted  and  evenly  applied.  The 
excess  of  silex  should  be  absorbed  with  a  cloth.  Another  method  is 
as  follows:  while  the  thin  silex  is  still  moist  upon  the  cast,  dust 
with  talcum  powder  and  when  dry,  rub  carefully  with  a  soft  cloth. 
The  licjuid-silex  bottle  should  be  kept  well  corked  and  no  particles  of 
plaster  i)e  permitted  to  get  into  it,  as  they  will  precipitate  and  spoil 
the  silex  for  use.  The  brush  must  be  well  washed  each  time  it  is  used. 
Packing  the  Base-plate. — The  cast  having  been  coated  either  with 
the  tin  or  with  the  lic|uid-silex,  the  counter  portion  of  the  flask  is  placed 
plaster  side  down,  upon  a  piece  of  sheet  iron  over  the  gas  stove.  The 
cast  portion  of  the  flask  is  placed  upon  the  sheet  iron  with  the  cast 

Fig.  436 


The  base-plate. 

downward,  and  one  edge  resting  upon  the  other  section  of  the  flask  so 
that  the  cast  does  not  touch  the  sheet  iron;  heat  is  applied  for  three 
or  four  minutes  or  until  the  plaster  is  as  hot  as  the  fingers  can  bear 
when  pressed  upon  it.  The  case  is  then  removed  from  the  sheet  iron 
and  a  piece  of  brown  or  black  rubber  large  enough  to  cover  the  cast  is 
placed  in  the  mold  in  the  flask.  If  there  is  any  doubt  of  the  rubber 
filling  the  mold,  an  extra  piece  should  be  added.  The  two  portions  of  the 
flask  are  placed  together  and  gently  pressed  in  the  flask  press  until 
closed.     (vSee  Figs.  468  to  470.) 

Vulcanization  of  the  Base-plate. — The  flask  is  then  clamped  or  bolted 
and  placed  in  the  vulcanizer  (see  Figs.  472  to  481),  and  sufficient  heat 
is  applied  to  raise  the  temperature  to  .320°  F.  and  sustained  for  fifty 
minutes.  When  the  flask  is  cold  the  case  is  removed  and  all  plaster 
cut  and  brushed  away. 

Finishing  the  Base-plate. — The  periphery  of  the  base-plate  is  trimmed 
with  a  vulcanite  file  to  the  desired  outline,  and  the  labial,  buccal,  and 
lingual  surfaces  are  scraped,  so  as  to  have  a  clean,  fresh-cut  surface  for 
the  attachment  of  the  teeth  and  contouring  rubber. 

Obtaining  the  Occlusion  Models. — The  base-plate.  Fig.  436,  is  placed 
in  the  mouth  and  the  patient  is  instructed  to  swallow;  when,  if  the 
conditions  are  favorable,  it  will  be  firmly  retained.  With  the  index 
finger,  pressure  should  be  exerted  upon  every  portion  of  the  base-plate 
to  see  if  this  tends  to  dislodge  it;  and  if  so,  the  cause  should  be  noted  to 
see  if  the  fault  can  be  corrected.  It  is  to  be  observed  if  the  labial  and 
buccal  frjena  are  sufficiently  relieved,  that  the  plate  at  the  canine  emi- 
nence is  as  high  as  can  be  worn,  and  that  the  distal  edge  of  the  plate  does 
not  extend  too  far  backward.  If  there  are  faults  that  cannot  be  cor- 
rected a  new  impression  should  be  taken  and  the  work  started  again.  In 
some  cases  the  soft  tissues  are  so  verv  tense  that  adhesion  will  not  tak^ 


OBTAINING   THE  OCCLUSION  MODELS.  485 

place  at  once.  In  such  cases  the  index-finger  of  the  left  hand  should  be 
placed  a<>;niiist  the  vault  of  the  base-plate  and  the  test  made  as  before, — 
when,  if  the  base-plate  sets  firmly  at  every  point  and  the  peripheral  line 
is  correct,  the  operator  may  be  assured  the  finished  denture  will  adhere 
after  it  has  been  in  the  mouth  a  short  time. 

A  satisfactory  base-plate  having  been  obtained,  wax  should  be  formed 
over  the  alveolar  ridge  of  the  base-plate  to  restore  the  contour  of  the 
gum  and  the  outline  of  the  teeth,  by  repeatedly  trying  in  the  mouth  and 
adding  to  or  taking  away  the  wax  until  the  desired  effect  is  produced. 
(Fig.  437.)     The  objects  sought  are:  (1)  that  the  hps  and  cheeks  be 

Fig.    437 


The  base-plate  with  wax  added  used  for  the  bite-plate. 

held  in  as  near  the  normal  condition  as  possible;  (2)  that  the  wax  be 
built  the  full  length  of  the  lip,  thus  indicating  the  incisal  line  of  the  teeth; 
(3)  that  the  occlusal  edge  of  the  wax  be  carved  to  receive  a  slight  im- 
print of  the  cusps  and  incisive  edges  of  all  the  lower  teeth,  and  (4)  that 
a  line  be  drawn  in  the  wax  to  indicate  the  median  line  of  the  face  and 
also  the  high  lip  line  at  the  highest  point  at  which  the  patient  can  elevate 
the  lip  by  muscular  action. 

Sufficiently  well-softened  pure  beeswax  should  be  placed  in  a  lower 
tray  and  a  perfect  impression  of  the  occlusal  and  incisive  surface 
and  at  least  half  the  length  of  the  lower  teeth  be  taken.  This  impres- 
sion may  be  filled  with  regular  dental  plaster  or  better,  Spence  com- 
pound, because  of  its  great  hardness. 

Teeth  of  suitable  size,  form  and  color  (see  Chapter  XII.),  should 
now  be  selected  and  the  patient  dismissed. 

The  base-plate  with  its  wax  occlusion  model  and  cast  of  the  lower 
teeth  should  be  adjusted  upon  an  anatomical  articulator.  (Fig.  438.) 
If  there  are  heavy  undercuts  in  the  base-plate,  they  should  be  filled  in 
with  soft  wax,  but  if  the  undercuts  are  not  suflacient  to  interfere  with 
its  easy  removal  from  the  supporting  cast,  no  wax  will  be  needed.  The 
cast  of  the  lower  teeth  should  be  adjusted  to  the  imprints  of  the  teeth 
in  the  occlusal  edge  of  the  wax  model  and  sufficient  regular  dental  plas- 
ter mixed  to  fill  the  base-plate  and  attach  all  to  the  articulator.  At- 
tention should  be  given  to  placing  the  case  squarely  upon  the  artic- 
ulator, the  occlusal  surface  of  the  teeth  parallel  with  the  low^er  bow,  and 


486 


VULCAXlZh'D    nriiHh-R   AS  A    BASE. 


thv  median  line  at  the  incisive  edge  of  the  teeth  four  inches  from  the 
condyles.  The  Snow  face-bow  in  connection  witli  the  Snow  ar- 
ticulator furnished  a  good  means  for  accurately  adjusting  the  case. 
Fig.  4o!)  siiows  wax  model  removed. 

Arranging  the  Teeth.     A  section  of  the  wax  model  extending  from  the 
median  line  and  tiie  iiigh  lip  line  hackward  to  the  first  molar,  upon 


Casts  mounted  upon  artioilator  :  wax  removeri  for  setting:  np  of  teeth  on  one  side. 

Fi...  v:<.\ 


Base-plate  on  articulator  with  wax  removed. 

one  side  only,  should  be  removed.  (Fig.  438.)  Arrange  the  teeth  in 
this  space  so  as  to  restore  the  contour  of  the  removed  wax,  and  at  the 
same  time  follow  the  instructions  in  Chapter  XII.  Wax  should  be 
melted  about  the  lingual  and  cervical  portion  of  the  teeth  to  securely 
fasten  them.  The  remaining  segment  of  wax  representing  the  molars 
should  now  be  removed  and  the  teeth  secured  in  their  position.     The 


PROVING  ANTAGONTZATION,   CONTOUR,  AND  EXPRESSION.     487 


opposite  side  is  treated  in  like  iiiauner.  The  contour  of  the  gum  is 
restored  by  aid  of  a  wax  spatula  and  the  addition  of  wax  where  needed. 
The  wax  can  be  nicely  smoothed  by  passing  it  through  the  Bunsen 
flame.  The  teeth  may  be  cleaned  of  wax  by  using  a  cloth  wet  with 
chloroform.  The  case  should  now  be  taken  from  the  articulator.  If  any 
wax  has  been  placed  upon  the  maxillary  surface  it  must  be  removed. 

Proving  the  Antagonization,  Contour,  and  Expression. — The  case  should 
be  placed  under  the  faucet  to  chill  the  wax  and  moisten  the  maxillary 
surface;  it  is  then  placed  in  the  mouth.  The  occlusion  must  first  be 
considered.  Examine  the  molars  and  bicuspids  w^ith  a  mouth  mirror 
and  use  a  thin  spatula  blade  to  determine  if  there  is  equal  pressure 
upon  both  sides.  The  antagonization  can  be  inspected  by  requesting 
the  patient  to  carefullv  close  the  teeth  in  various  positions.     The  in- 


Teeth  set  up  and  strings  in  place. 

cisors  are  studied  by  taking  a  position  in  front  of  the  patient,  and  re- 
questing the  patient  to  raise  the  upper  lip,  thus  observing  the  location 
of  the  median  line  and  the  inclination  of  each  of  the  six  anterior  teeth. 
(See  Fig.  457.)  The  contour  is  proven  by  studying  the  face.  Standing 
at  the  side  of  the  patient  observe  the  profile  and  see  that  the  upper  lip 
is  in  harmonious  relation  to  the  lower,  also  that  the  lip  has  its  normal 
fulness  throughout  its  length.  (See  Figs.  455  and  456.)  The  operator 
should  again  take  a  position  in  front  of  the  patient.  Attention  should 
be  given  to  the  incisive  fossae  and  canine  eminences,  and  especial  atten- 
tion be  given  to  the  triangles  formed  by  the  wings  of  the  nose  and  cheeks, 
which  are  influenced  by  the  apices  of  the  canines.  If  it  is  desirable, 
the  cheeks  can  be  contoured  to  a  limited  extent  by  the  addition  of  wax 
contours  (plumpers)  over  the  molars.  Having  obtained  the  desired  re- 
sults in  a  state  of  rest,  the  operator  should  engage  the  patient  in  conver- 
sation and  observe  the  effect.     The  case  is  now  cleansed  of  the  secre- 


488  VULCAyiZED  RUBBER  AS  A    BASE. 

tions  of  the  month  hv  liohUii*;  iiiKk-r  the  faucet  and  (h'viny;  wltli  a  cloth. 
If  any  of  the  teetli  are  k>o,se,  they  must  be  securely  fastened,  and  the  wax 
smoothed  witliout  chaiiLriiiii;  its  form. 

The  double  vulcanization  method  is  especially  adapted  for  restoring 
the  contour  and  expression,  because  this  work  is  done  in  wax,  when  the 
wax  form  can  l)e  easily  and  ])erfectly  reproduced  in  vulcanite. 

Preparing  the  Case  for  Flasking — Strings  are  used  for  outlining 
the  festoons  and  periphery  of  the  gum.  The  object  of  the  festooning 
string  at  the  cervical  portion  of  the  teetli  is  to  give  the  proper  thickness 
to  the  margin  of  the  gum.  The  string  used  for  this  purpose  is  waxed 
dental  floss,  twisted  very  hard,  doubled,  and  twisted  again.  In  doub- 
ling, the  loop  will  show  the  direction  in  which  it  should  be  twisted  the 
second  time.  Wax  the  string  well  with  softened  wax  and  apply  it  by 
grasping  the  left  heel  of  the  plate  between  the  fingers  and  thumb  of  the 
left  hand,  with  the  occlusal  surfaces  of  the  teeth  upward;  place  one  end 
of  the  string  at  the  distal  surface  of  the  second  molar,  pressing  it  gently 
into  the  wax;  outline  the  margin  of  the  gum,  using  the  wax  spatula  to 
carry  the  string  well  into  the  interproximal  spaces.  The  peripheral 
string  should  be  well-waxed  wrapping  twine,  placed  at  the  outer  edge 
of  the  wax,  and  secured  in  place  by  melted  wax  made  smooth  with  a 
hot  spatula.     (See  Figs.  440,  449,  and  450.) 

The  next  step  is  to  cover  the  buccal  and  labial  surfaces  with  a  strip  of 
No.  60  tin  foil.  Instructions  are  necessary  in  applying  the  tin  over 
the  strings.  The  No.  3  instrument  of  the  Evans  set  of  carvers  (Fig. 
40f)),  is  especially  adapted  for  adjusting  the  tin  foil.  The  strip  of  foil 
is  placed  over  the  wax  and  teeth  and  pressed  as  closely  as  possible  into 
position  with  the  fingers.  Hold  the  work  in  the  left  hand,  seize  the 
ivory-pointed  instrument  by  the  hand  grasp,  rest  the  thumb  upon  the 
occlusal  surface  of  the  second  molar  and  burnish  the  tin  closely  to  the 
tooth  and  against  the  festoon  string.  Continue  this  operation  with  all 
the  teeth.  With  a  sharp  chisel  cut  away  the  excess  of  tin  upon  the 
teeth  to  within  one-sixteenth  of  an  inch  of  the  festoon  string.  (See  Fig. 
441.)  After  readjusting  the  tin  about  the  teeth,  the  metal  must  be 
burnished  over  the  string  to  give  the  desired  thickness  of  the  gum  and 
the  contour  of  the  festoon.  This  is  done  hy  holding  the  plate  and 
burnisher  in  the  same  manner  as  before.  The  instrument  must  extend 
one-sixteenth  of  an  inch  behind  the  string  and  at  the  same  time  must 
rest  upon  the  body  of  the  tooth  while  pressing  the  tin  down  over  the 
festoon  string.  By  this  means  a  proper  thickness  and  contour  is  given 
the  margin  of  the  gum,  without  forming  an  unnatural  beaded  edge. 
After  all  the  teeth  have  been  thus  treated,  the  position  of  the  plate 
should  be  reversed  in  the  left  hand,  so  that  the  thumb  of  the  right  hand 
may  rest  upon  the  periphery  of  the  plate  while  burnishing  the  tin  from 
the  festoons  towards  the  edge  of  the  plate.  With  a  pair  of  sharp  curved 
scissors  trim  the  tin  flush  with  the  peripheral  string,  but  do  not  permit 
it  to  overlap  the  vulcanite  base-plate.  (See  Fig.  441 .)  The  case  is  now 
ready  for  tinning  the  lingual  surface.  Use  No.  60  foil  and  if  the  vault 
is  a  high  one,  slit  the  tin  from  the  middle  of  one  side  to  the  centre. 
Place  the  inner  end  of  the  slit  over  the  middle  of  the  vault,  and  one  edge 


FLASKING.  489 

of  the  slit  along  the  median  ridge  to  the  incisor  teeth;  press  the  side  of 
the  foil  gently  against  the  wax  and  teeth ;  press  the  other  half  of  the  tin 
in  the  same  manner  into  position,  permitting  the  slit  portion  to  overlap 
the-  first  half.     With  sharp  scissors  trim  the  tin  nearly  down  to  the 

Fig.  441 


Tin-foil  applied  to  labial  and  buccal  portions  of  denture. 

teeth.  Remove  the  foil  and  place  it  upon  a  plaster  or  metal  cast^ 
having  well-defined  rugae  and  burnish  the  rugse  into  the  foil.  Remove 
the  foil,  turn  it  over  and  fill  the  impressions  of  the  rugse  with  wax,  also 
smear  the  remainder  of  this  surface  with  a  thin  layer  of  wax;  now  re- 


Fig.  442 

^^^pH^HKiVL^^^  ^'Nj 

i^^l 

■■^^y''"iiT "" 

^^^^^^H 

H^HjIil  ^^^^JESMRySfc  ■  %     ' 

^^^^B^wfc       .   ^^ 

^IM| 

^n^^_ 

^H 

HBSHhi 

Tin-foil  applied  to  lingual  surface.     Showing  rugae  and  carving  of  the  lingual  surfaces  of  the  teeth. 

place  the  waxed  surface  against  the  vault  of  the  plate  and  nicely  ad- 
just wath  the  fingers.  The  tin  must  be  securely  burnished  against  the 
teeth.  The  lingual  contour  of  the  teeth  -  is  reproduced  by  burnishing 
their  forms  in  the  tin.     (See  Fig.  442.) 

1  A  suggestion  of  Dr.  A.  DeWitt  Gritman  of  the  University  of  Pennsylvania. 
2 In  the  International  Dental  Journal  for  August,  1905,  Dr.  William  M.  Fine  describes  and  beau- 
tifuUv  illustrates  his  method  of  carving  the  lingual  contour  of  the  teeth. 


490  VULCANIZED   RVIIUER  AS  A    BASE. 

Flasking.  A  flask  with  a  narrow  rim  is  imperative.  The  Star  flask 
will  do  \(Ty  well,  hut  one  made  by  the  Cleveland  Dental  ]\Ianufaetur- 
\\\)l  Company,  railed   the  Wilson  flask,  will  better  serve  the  purpose. 

Fig.  443 


Cast  and  denture  invested  in  Wilson-flask. 


This  fla.sk  is  desiijned  to  l)e  used  with  the  Donham  elamp.     (See  Figs. 
4()8  and  4G4.) 

The  maxillary  surface  of  the  case,  having  been  cleansed  of  wax,  is 
filled  with  Spence's  compound,  which  forms  a  cast  upon  which  the 
denture  is  vulcanized.    This  vulcanization  cast  should  be  not  less  than 


Fig.  444 


Counter  portion  of  Wilson  lla.sk. 


one-fourth  of  an  inch  thick  at  the  thinnest  portion  of  the  vault,  and 
should  not  overlap  the  tin  facing.  In  one  hour  this  cast  will  be  suflS- 
ciently  hard  to  place  in  the  first  section  of  the  flask  with  regular  dental 
plaster.     (See  Fig.  443.)     The  peripheral  string  will  be  a  great  aid 


SKPARATfNd    THE   FLASK. 


491 


in  outlining  the  denture  in  the  investment  plaster.  After  the  plaster 
has  set  it  is  coated  with  a  separating  fluid,  and  then  held  under  the 
I'aueet  so  as  to  moisten  the  tin  foil  and  thus  facilitate  the  flowing  of 
plaster  into  the  interproximal  si)aces  at  the  time  the  flasking  is  com- 


Invested  case:    flask  opened  and  wax  removed  ready  for  packing. 
Fig.  446 


Lower  portion  of  flask,  showing  invested  base-plate  and  outlet  vents  for  the  excess  of  vulcanite. 

pleted.  The  flask  should  stand  about  twenty-five  minutes  and  then 
be  placed  over  the  stove  in  a  stew-pan  of  cold  water  to  be  heated  up  as 
before  described. 

Separating  the  Flask.— When  the  heat  of  the  water  indicates  the 


492 


VULCANIZED  RUBBER  AS  A   BASE. 


time  of  opening,  the  flask  is  grasped  with  a  cloth  holder  in  the  left  hand 
and  separated  h\  the  point  of  a  knife  blade  or  wax  spatnla  inserted  at 
the  heel  of  tlie  flask.  The  instrument  should  be  guarded  by  the  thumb 
and  finger  of  the  right  hand  to  avoid  the  possil)ihty  of  marring  the  ease. 
The  strings  and  as  mueii  of  the  wax  as  possibk'  are  removed  with  the 
spatula,  when  the  remainder  is  removed  by  pouring  boiling  water  upon 
it;  then  with  a  cloth  the  vulcanite  base-plate  and  tin  lining  are  w'iped 
dry.  (Figs.  445  and  446.)  The  excess  space  is  cut  with  small  gates 
(see  Fig.  446),  and  the  separated  flask  is  placed  over  the  sheet  iron  to 
warm  as  pre\'iously  described. 

Packing. — Sufficient  Gilbert  Walker's  granular  gum  or  pink  rubber 
is  cut  into  strips  to  form  a  layer  of  one  thickness  over  the  tinnerl  surface. 
First  pack  a  narrow  strip  of  red  rubber  about  the  pins  (Fig.  447,  C), 
and  small  square  or  triangular  pieces  of  granular  gum  between  the 
cervical  portions  of  the  teeth.  The  strips  of  granular  gum  are  then 
placed  over  the  labial  and  buccal  surfaces  of  the  matrix  with  the 
fingers  and  wax  spatula  so  that  no  space  remains  through  which  the 
red    rubber    can    escape.     The  strip   of    red  rubber    about    the   pins 


Invested   case  partially   packed.    A,  half  circle    of    granular  gum;    B,  thin  granular  gum;    C. 
strip  of   red  rubber  about  the  pins. 

should  be  pressed  down  with  a  wax  spatula  to  form  a  symmetrical 
outline.  Apiece  forming  half  a  circle  of  granular  gum  is  then  placed 
over  the  anterior  portion  of  the  lingual  surface  (Fig.  447,  A),  and  with 
the  wax  spatula  the  circular  edge  is  joined  to  the  red  rubber  about 
the  pins  of  the  teeth.  Apiece  sufficiently  large  when  stretched  to  half 
its  thickness  (Fig.  447,  B),is  then  applied  over  the  remaining  portion  of 
the  lingual  surface,  and  its  edges  are  united  to  the  contiguous  rubber. 
Strips  of  red  rubber  are  then  placed  over  the  teeth  to  nearly  but  not  quite 


FINISHING. 


493 


fill  the  mold.  A  separating  cloth  of  closely  woven  cotton,  or  the  cloth 
removed  from  the  rubber  after  the  sizing  has  been  washed  out,  is  satu- 
rated with  water  and  placed  over  the  rubber  in  the  mold — when  the  two 
sections  of  the  flask  are  placed  together.  If  the  packing  has  been  ex- 
peditiously done  and  the  rubber  is  sufficiently  warm,  it  is  placed  in  the 
flask  press  and  gentle  pressure  applied.  The  flowing  of  the  rubber 
should  be  followed  every  ten  seconds  with  a  partial  turning  of  the  screw 
until  the  flask  is  closed.  The  flask  is  then  removed  from  the  press  and 
separated.  If  there  is  not  an  excess  of  rubber,  the  cloth  will  easily 
separate  from  the  rubber,  but  should  there  be  strong  adhesion,  satura- 
tion of  the  cloth  with  water  will  facilitate  its  removal.  If  the  plaster  has 
become  nearly  cold  while  packing,  the  flask  should  be  placed  in  boiling 
water  for  five  minutes  before  it  is  pressed. 

Vulcanizing.^ — The  case  is  vulcanized  in  the  same  manner  as  the  base- 
plate. Preference  is  given  to  low  temperature  and  long  time,  300° 
F.  for  three  hours  from  the  time  of  applying  the  heat.  It  should  not 
be  taken  from  the  flask  until  it  is  cold. 

Finishing. — After  washing  to  remove  the  loose  plaster,  the  tin  can  be 
easily  stripped  oft',  and  the  excess  vulcanite  filed  from  the  periphery  of 
the  denture.  A  sharp  chisel  should  be  used  to  trim  about  the  labial  and 
buccal  surfaces  of  the  teeth,  but  the  lingual  surface  should  be  trimmed 
v.'ith  a  scraper.    The  file  marks  about  the  periphery  of  the  plate  should 

Fig.    448 


Completed  denture  for  case  A, 

be  removed  with  fine  sandpaper.  The  labial,  buccal  and  lingual  sur- 
faces are  buffed  with  felt  wdieels  and  cones  carrying  pulverized  pumice 
and  water.  The  spaces  between  the  teeth  are  best  reached  with,  a  stiff 
bristle  brush  wheel,  using  wet  pumice.  All  the  surfaces  including  the 
maxillary,  are  glossed  by  using  a  rapidly  revolving  soft  brush  wdieel  and 
whiting  wet  wdth  alcohol  or  water. 

Case  A.— Figs.  438,  439,  440,  441,  442,  448.  Constructed  for  a 
lady  about  fifty-five  years  of  age,  and  of  the  bilious  temperament 
modified  by  the  nervous.  Teeth,  S.  S.  W.  natural  forms,  mold  num- 
ber 227,  shade  number  47.  The  illustration  will  show  that  nearly  all 
the  teeth  were  ground  for  the  purpose  of  occlusion  or  to  represent  age. 
and  the  laterals  to  represent  a  personal  peculiarity.    When  the  finished 


41)4 


VULCAMZKD  RUBBER   AS  A    BASE. 


(k'liture  was  placed  in  the  mouth  it  was  observed  that  the  centrals  and 
canines  were  too  much  curved  in  the  long  axis  of  the  teeth.  The  labial 
surface  of  these  teeth  was  ground  to  give  them  the  square  angular 


Flo.  449 


Full  u|)|)er  ami  lower  cases  waxed  up,  shr>winK  larRO  contours  and  method  of  using  waxed  string. 

Fig.  450 


Completed  dentures  for  case  B.    Note  large  contoms  on  buccal  surface  of  upper  plate. 


form  indicative  of  the  bilious  temperament,  thus  completing  the  har- 
mony in  form.  These  ground  surfaces  were  then  given  a  dull  polish 
as  described  in  the  paragraph  "Grinding  and  Polishing"  imder  the 


ILLUSTRATIVE  CASES. 


495 


heading — "  General  Technique  Instruction."  These  photographs  were 
made  before  the  grinding  of  the  labial  surfaces.  Attention  is  called  to 
the  canine  eminences  and  the  incisive  and  canine  fossae. 


Fia.  451 


Lingual  surfat-e  of  upper  plate  shown  in  Fig.  450. 
Fig.   4.52 


Occlusal  surface  of  lower  plate  shown  in  Fig.  450. 
Fig.    4.53 


Maxillary  surface  of  plate  showu  in  Fig.  -150. 


Case  B. — Patient  about  forty-five  years  of  age,  of  a  strong  sanguine 
temperament,  with  a  nervous  temperament  modification.  The  patient 
had  W'Orn  artificial  dentures  for  fifteen  years.     Teeth  used,  S.  S.  W. 


496 


VULCANIZED  RUBBER  AS  A  BASE. 


natural  forms,  mold  number  202,  shade  number  40.  Attention  is  called 
to  the  extensive  contours;  also  the  general  rounded  outline  indicative 
of  a  sanguine  temperament.     (Figs.  449  to  457  inclusive.) 

Case  C. — Lady  thirty  to  thirty-five  years  of  age.  Marked  nervous 
temj)('rani(Mit  with  sanguine  temperament  modification.  Teeth  S.  S. 
W.  natural  forms,  mold  number  215,  shade  mmiber  31.     (Fig.  458.) 


Manilihuliir  surfarc  of  i)liitL'  as  shown  in  Fig.  450. 
Fig.  455  Fni.  4.')0 


Profile  view  of  patient  described  as  case  B 
Before  the  insertion  of  the  denture. 


ew  of  patient  with  denture  in  place. 


Case  D. — Lady  about  fifty  years  of  age.  Sanguo-lymphatic  tempera- 
ment. Teeth,  S.  S.  W.  natural  forms,  mold  number  223,  shade  number 
40.  Gum  restoration  about  the  thickness  of  a  sheet  of  base-plate  wax. 
Onlv  suitable  for  construction  bv  single  vulcanization  method.  (Fig. 
459.) 


ILLUSTRATIVE  CASES. 


497 


Three-quarter  view  of  patient  with  denture  in  place. 
Fig.  458 


Completed  denture  for  case  C. 
Fig.  459 


Denture  for  case  D. 


32 


498  VULCANIZED  RUBBER  AS  A  BASE. 

FULL   UPPER:    SINGLE   VULCANIZATION   METHOD. 

A  Spence  compound  cast  is  made  from  a  plaster  impression,  upon 
which  is  formed  a  base-plate  of  pink  paraffin  and  wax,  modelling  com- 
pound, or  any  of  the  hard  gum  base-plate  materials  upon  the  market. 
The  wax  is  arranged  in  the  same  manner  as  upon  the  \ulcanite  base- 
})late  for  obtaining  the  occlusion  models.     (Chapter  X.) 

The  cast  and  occlusion  models  are  attached  to  the  articulator.  The 
teeth  are  arranged,  the  gum  contoured,  and  the  case  tried  in  the  mouth. 
It  is  obvious  that  it  will  be  more  difficult  to  prove  the  occlusion,  con- 
tour and  expression,  because  of  the  imperfectly  fitting  trial  plate. 
(Fig.  440.)  The  denture  is  then  cleansed  of  the  secretions  of  the 
mouth,  dried,  and  the  tin  foil  adjusted  upon  the  wax.  With  a  hot 
spatula  and  a  little  wax  the  case  is  sealed  to  the  cast.  The  cast  is  then 
well  saturated  with  water,  when  it  can  be  easily  removed  from  the  articu- 
lator by  inserting  the  end  of  a  knife  blade  between  the  cast  and  attach- 
ing plaster.    It  is  then  ready  for  flasking,  as  in  the  previous  case. 

The  labial  and  buccal  surfaces  are  packed  with  granular  gum  cr  pink 
rubber  as  in  the  other  method,  but  the  lingual  surface  is  packed  entirely 
with  red  rubber.  Care  should  be  exercised  to  properly  distril)ute 
the  rubber  about  the  mold  and  to  use  no  excess  for  the  first  closing  of 
the  flask.  After  removing  the  separating  cloth,  sufficient  rubber  is 
added  to  fill  the  deficiencies  and  give  a  slight  excess  when  the  flask  is 
closed.     It  is  then  vulcanized  and  finished  as  in  the  former  case. 

FULL  UPPER:  SINGLE  VULCANIZATION  SUB-METHOD.      . 

The  procedure  is  the  same  as  the  preceding  method,  up  to  the  pre- 
paring of  the  case  for  flasking.  The  strings  and  tin  foil  are  not  applied, 
but  the  wax  form  is  nicely  smoothed  in  the  Bunsen  flame  or  by  use  of 
soft  cloth  or  cotton  and  some  solvent  of  wax, — chloroform  is  the  least 
objectionable.  The  case  is  then  flasked  and  the  rubber  packed  against 
all  portions  of  the  plaster,  except  the  cast,  which  should  always  be 
finished  either  with  the  thin  tin  and  soap,  or  silex.  Owing  to  the  rough 
surface  produced  by  contact  with  the  plaster,  it  will  be  necessary  to 
file,  scrape  and  sandpaper  the  entire  labial,  buccal  and  lingual  surfaces 
before  they  are  ready  for  polishing,  thus  more  than  offsetting  the  time 
saved  by  not  applying  the  strings  and  heavy  foil.  The  surface  pro- 
duced is  not  as  hard  and  dense  as  that  obtained  from  contact  with  the 
metal. 

FULL  LOWER:  DOUBLE  VULCANIZATION  METHOD. 

The  only  difference  in  method  of  constructing  the  lower  and  upper 
dentures  is  in  the  application  of  the  peripheral  string,  which  in  the 
lower  should  completely  encircle  the  base-plate;  while  in  the  upper 
the  distal  edge  is  not  outlined  from  heel  to  heel. 


GENERAL   TECHNIQUE  INSTRUCTIONS.  499 

FULL  LOWER:    SINGLE   VULCANIZATION   METHOD. 

The  one  detail  in  the  construction  of  this  lower  denture,  which  differs 
from  that  of  the  upper  one,  is  the  necessity  for  addins;  a  16-gauge  soft 
ir(Mi  wire  stiftener  over  the  wax  base-plate,  to  give  rigidity  in  securing 
the  wax  occlusion  models,  and  later  while  proving  the  occlusion  by  try- 
ing in  the  mouth.  The  wire  is  removed  from  the  flask  with  the  wax. 
See  Chapter  X.  for  other  methods  of  taking  the  bite. 

PARTIAL  CASES. 

These  are  usually  made  by  the  single  vulcanization  or  sub-method. 
They  differ  from  a  full  case  in  the  manner  of  flasking  and  packing, 
which  will  be  explained  under  the  heading  "Flasking." 

GENERAL  TECHNIQUE  INSTRUCTIONS. 

Flasking. — Rule  I. — All  full  cases  and  partials  with  gum  restora- 
tions should  be  flasked  so  as  to  separate  at  the  periphery  of  the  wax. 
The  "Wilson  or  Star  flask  is  best  adapted  to  this  class  of  work.  If  the 
Star  flask  is  used,  the  case  must  first  be  imbedded  in  the  narrow  rim 
portion  of  the  flask. 

Rule  II. — All  partial  dentures  without  gum  restorations,  and  most 
repairs  must  be  so  imbedded  in  the  first  section  of  the  flask,  that  the 
teeth  are  held  securely  in  apposition  with  the  cast,  when  the  flask  is 
opened.  The  Star  flask,  using  the  wide  rim  flrst,  or  any  of  the  various 
forms  of  flasks  of  the  Whitney  type,  are  best  for  these  cases.  Under 
this  rule  the  cast  and  denture  are  imbedded  in  the  encasing  plaster  of 
the  first  section  of  the  flask,  the  wax  only  being  exposed.  The  plaster 
in  the  first  section  must  be  so  shaped  that  the  two  portions  of  the  flask 
can  be  easily  separated. 

In  comiection  with  this  rule,  attention  is  called  to  a  class  of  repair 
cases  that  perplex  the  no^-ice;  namely,  those  having  an  extensive  frac- 
ture upon  both  the  lingual  and  buccal  or  labial  surfaces.  This  diffi- 
culty in  flasking  is  overcome  by  attaching  one  or  more  shafts  of  wax, 
one-fourth  inch  in  diameter,  at  suitable  locations  over  the  fracture 
upon  the  labial  or  buccal  surface.  The  shaft  of  wax  must  be  sufficiently 
long  to  extend  through  the  encasing  plaster.  ^Yhen  the  plaster  has 
hardened,  a  portion  of  the  wax  shaft  and  the  surrounding  plaster  is  cut 
away  to  form  a  cone-shaped  depression,  which  will  be  filled  in  with  the 
plaster  in  the  top  section  of  the  flask.  These  wax  shafts  will  form 
openings  through  which  the  rubber  can  be  packed,  and  which  are  to  be 
filled  with  rubber.  After  vulcanization  the  shaft  of  rubber  may  be  re- 
moved with  a  mechanical  saw.     (See  Figs.  515  and  516.) 

The  salts  NaCl  and  KjSOi  should  never  be  used  to  hasten  the 
setting  of  the  plaster  in  the  flask,  as  they  weaken  it  and  make  the  warp- 
ing of  the  plate  during  the  closure  of  the  flask  more  liable. 

Packing. — Wlien  the  case  is  prepared  for  packing  as  described  in  the 
double  vulcanization  process,  some  operators  prefer  placing  the  cold 


500  VULCANIZED  RUBBER  AS  A  BASE. 

rubber  in  the  flask,  because  it  is  firmer  and  easier  to  handle,  and  will 
soon  become  warm  and  plialile  from  the  heat  of  the  flask;  other  oper- 
ators j)refer  warmino-  tlu>  rubber  as  well  as  the  flask,  and  it  is  better  for 
all  students  to  do  so  until  they  have  gained  dexterity  and  confidence  in 
their  ability  to  quickly  pack  the  case  before  the  flask  becomes  too  cold. 

A  convenient  way  to  warm  the  rubber  is  to  heat  in  hot  water  a  piece  of 
soap-stone  (a  small-sized  foot  warmer),  and  after  the  rubber  is  cut  into 
suitable  strips,  it  is  placed  upon  the  stone.  By  this  means  the  stone 
does  not  become  too  hot,  and  holds  the  heat  well.  Another  device  is 
a  porcelain  dish  upon  which  the  rubber  is  placed  and  is  kept  warm  by 
placing  the  dish  upon  a  receptacle  containing  hot  water.  A  specially 
constructed  warming-oven  as  described  by  Drs.  Essig  and  Evans  in 
the  former  editions  of  this  book,  serves  an  excellent  purpose.  (See  Fig. 
47 1 .)  It  is  very  essential  in  packing  a  case  that  the  rubber  shall  be  evenly 
distributed  through  the  mold  so  that  in  closing  the  flask  there  W'ill  be 
no  undue  pressure  at  any  point,  thus  avoiding  a  warped  denture  or 
elongated  teeth. 

Vulcanizing. — For  convenience,  cleanliness  and  uniformity  of  results, 
dental  vulcanization  is  accomplished  in  a  specially  constructed  machine, 
called  a  vulcanizer  (see  Figs.  472-481).  which  is  a  steam-tight  boiler. 
The  operation  can  be  accomplished  in  a  sand,  glycerine  or  oil  bath,  but 
this  is  not  desirable  for  obvious  reasons.  The  time  of  vulcanizing  will 
be  influenced  by  both  temperature  and  the  surrounding  medium.  Vul- 
canization begins  at  248°  F., but  at  that  temperature  it  would  require 
many  hours;  at  280°  F.,  it  will  require  5^  hours;  at  300°  F.,  2.}  hours; 
and  at  320°  F.,  fifty  minutes.  The  medium  surrounding  the  flask  in 
the  vulcanizer  must  be  either  water,  steam  or  air.  The  time  re- 
quired to  produce  the  same  result  will  be  in  inverse  ratio  to  the 
conducting  power  of  the  medium;  w^ater  being  the  best  conductor  of 
heat  will  require  the  least  time,  steam  second,  and  air  being  the  poorest 
conductor,  wull  require  the  longest  time.^  It  is  always  best  to  permit 
the  vulcanizer  to  stand  until  it  is  cold  before  opening,  but  wdien  it  is 
necessary  to  expedite  matters,  the  steam  may  be  blown  off,  the  vul- 
canizer opened,  and  the  flask  be  set  in  a  pan  of  cold  water.  This  last 
procedure  would  be  condemned  by  some,  but  ow  ing  to  the  poor  con- 
ducting and  radiating  property  of  plaster,  it  is  doubtful  if  this  method 
of  cooling  ever  accounts  for  fractured  teeth.  Under  no  condition  how- 
ever should  the  flask  be  opened  until  the  plaster  in  the  centre  of  the 
flask  is  cooled  to  blood  heat,  which  will  be  sometiine  after  the  flask  is 
cold  if  placed  in  water. 

Finishing. — The  filing  is  done  with  a  rather  coarse  file  especially 
made  for  this  work.  See  Fig.  483.  A  seven  or  eight  inch  half-round 
file  having  an  oval  and  a  flat  side,  a  coarse  and  a  fine  end,  is  a  very 
desirable  instrument.     The  cutting  is  done  with  a  push  stroke.     A' 

iThe  wTiter's  custom  is  to  have  the  flask  submerged  in  water  and  usesuflBcient  heat  to  reach 
the  required  vulcanizing  point,  (300°  F.), in  about  thirty  minutes,  and  to  maintain  that  temperature 
for  two  and  one-half  hours;  but  when  time  is  an  object,  to  take  thirty  minutes  to  attain  the 
320°  F.,  and  maintain  that  temperature  for  fifty  minutes. 


INSTRUMENTS  USED  IN  VULCANITE  WORK,  50I 

round  or  rat-tail  file  is  also  very  useful.  For  scraping  and  trimming 
the  plate,  short  shank  Kingsley  scrapers  numbers  1  and  5,  and  an  Ivory 
scraper  number  9,  and  a  Wilson  or  a  Spaulding  chisel,  make  a  very 
complete  equipment.  See  Figs.  484-487.  These  instruments  should 
be  kept  very  sharp  by  grinding  and  honing.  The  sandpapering  is 
done  with  a  two  inch  square  piece  of  number  o-  or  1,  followed  with 
number  00  paper.  The  paper  is  cut  into  squares  by  placing  the  sand 
side  down  over  a  crevice  and  cutting  with  a  knife.  Various  substances 
are  used  for  buffing  wheels  and  cones,  but  felt  has  proven  the  most 
satisfactory.  The  wheels  have  either  a  square  or  a  knife-edge.  The 
knife-edge  soon  becomes  so  blunt  that  it  fails  to  do  the  work  for  which 
it  was  designed.  This  difficulty  can  be  overcome  by  using  a  worn-out 
half-round  file  ground  to  a  sharp  edge,  held  by  an  end  grasped  in  each 
hand,  when  the  felt  wheel  can  be  quickly  and  safely  turned  to  shape. 
The  felt  carries  the  abradant,  of  which  pumice  is  the  best,  and  must 
be  kept  well  moistened;  otherwise  the  vulcanite  will  be  heated  and 
possibly  warped.  The  wheel  should  be  run  at  a  moderate  speed,  and 
the  hands  holding  the  work  firmly  against  the  felt  carrier  must  be  kept 
in  constant  motion,  so  that  symmetrically  curved  surfaces  may  be 
formed,  and  not  ridges  and  grooves,  as  the  result  of  too  long  contin- 
ued contact  at  any  one  place.  A  large  and  small  size  of  each  of  the 
forms  of  the  buffers  used  should  be  provided.  A  stiff  converging  bristle 
brush-wheel,  in  which  the  bristles  have  been  worn  or  cut  away  one-half, 
will  be  more  effective  for  buffing  between  the  teeth.  Striking  the  work 
against  the  moderately  revolving  brush  will  cause  the  bristles  to  reach 
the  innermost  spaces.  As  before  stated,  the  glossing  is  done  by  using 
a  rapidly  revolving  soft  bristle  brush-wheel  and  whiting  wet  with 
alcohol  or  water.  Very  good  results  can  be  obtained  by  rubbing  the 
surface  of  the  vulcanite  in  the  hand  with  dry  plaster  of  Paris. 

Grinding  and  Polishing  the  Teeth — It  will  often  be  necessary  to 
grind  the  exposed  surfaces  of  the  teeth,  which  should  again  be  polished. 
The  abraded  surface  should  be  well  sandpapered.  The  paper  is  held 
against  the  ball  of  the  thumb  which  will  conform  the  paper  to  the  sur- 
face of  the  teeth  and  greatly  facilitate  the  removal  of  the  facets  formed 
by  the  grind-stone.  It  is  then  buffed  with  the  felt  wheel  and  pumice; 
or  a  specially  prepared  rubber  wheel  can  be  obtained  for  this  work. 

Notching  the  Cervical  End  of  the  Teeth. — In  some  cases  where  there 
is  gum  restoration,  it  is  desirable  not  to  have  the  rubber  overlap  the 
cervical  end  of  a  tooth,  and  in  these  cases  cruciform  notches  should  be 
cut  in  the  cervical  end  with  a  small  knife-edged  stone,  into  which  the 
rubber  will  flow  and  harden  and  aid  in  supporting  the  tooth. 

INSTRUMENTS    AND   APPLIANCES  USED  IN   VULCANITE  WORK. 

Wax  Spatulas. — The  instruments  shown  in  Figs.  460  and  461,  are 
some  very  useful  forms.  The  Evans 'numbers  2  and  3  and  one  of  the 
others,  will  meet  every  requirement. 


502 


VULCAMZED  RUBBER  AS  A  BASE. 

Fig..  461 


b  '-J 


Fig.  400 


^y 


Evans'  carving  tools. 


Wax  spatulas:     Dorance,  Burchard,  Gritman. 


FLASKS. 


503 


Flasks. — There  are  a  great  many  varieties  of  vulcanite  flasks  upon 
the  market.  They  are  made  of  iron  and  brass.  Iron  has  the  greater 
affinity  for  oxygen  and  sulphur  in  vulcanizing  and  so  is  not  as  desir- 
able as  brass  for  this  purpose.     The  brass  flasks  are  the  more  easily 


Fig.   462 


Star  flask. 


cleaned.    Each  time  they  are  used,  they  should  be  thoroughly  cleaned 
with  a  stiff  brush  and  sapolio. 

The  Star  flask  is  one  of  the  oldest  forms,  and  being  reversible,  is  prob- 
ably adapted  to  more  cases  than  any  other.  (Fig.  462.)  The  Wilson 
flask  is  characterized  by  a  very  narrow  rim  upon  the  lower  section,  with 


504 


VULCANIZED  RUBBER  AS  A  BASE. 


a  correspondingly  wide  rim  in  the  npper  section.  It  is  designed  to  l)e 
used  for  full  cases  only  and  with  the  Donham  spring  clamp.  (Fig.  463.) 
The  Donham  flask  is  shown  in  the  Donham  spring  clamp.     (Fig,  464.) 


Fig.  463 


Wilson  flask. 


Fig.    464 


Fig.  465 


Donham  clamp  and  flask. 


Whitney  flask. 


The  Whitney  flask  is  very  much  used.  There  are  two  sizes,  the  lar- 
ger being  five-sixteenths  of  an  inch  deeper  than  the  smaller.  Fig.  405 
shows  the  regular  size  with  springs  upon  the  bolts  to  aid  in  closino-  the 
flask.  ^ 


FLASKS. 


505 


The  box  flask  is  designed  for  interdental  splints  and  any  extra  large 
pieces  of  vulcanite.  It  is  made  in  two  sizes,  one  as  large  as  can  be 
used  in  a  two-flask  ^•ulcanizer  and  the  other  for  the  three-flask  vul- 
canizer.     (Fig.  466.) 


Fig.  466 


Box  flask. 


Fig.  468 


Edson  flask 


S.  S.  W.  No.  1  press. 


The  Edson  flask  is  especially  designed  for  the  Edson julcanizer,  and 
may  be  used  for  both  vulcanite  and  celluloid.     (Fig.  46  / .) 


506 


VULCANIZED  RUBBER  AS  A   BASE. 


Flask  Presses. — The  flask  press  is  an  indispensable  appliance  in  a 
well-ecjiiipped  laboratory  (P'igs.  468,  469,  470),  and  yet  probal)ly 
its  improper  use  has  caused  more  misfit  vulcanite  dentures  than  all 
other  causes.  When  the  principles  involved  in  the  flask  press  and  its 
use  are  understood,  there  should  be  no  trou})l('  in  handling  it.     All 

Fig.  470 


Buffalo  No.  2  press. 


Dr.  E.  Wilson's  press. 


plasters  expand  and  are  compressible,  some  excessively  so.  French's 
regular  dental  plaster  is  the  best  and  most  commonly  used  by  the  pro- 
fes.sion,  so  these  statements  are  in  connection  with  this  plaster.  A 
molar  tooth  one-half  inch  in  diameter  under  a  thousand  pounds 
pressure  would  be  driven  into  well  set  plaster  one-twentieth  of  an  inch. 
Rubber  when  cold  is  very  tenacious  and  will  resist  a  very  heavy  pressure 
for  a  short  time,  but  will  gradually  yield.  Plaster  compresses  to  its  full 
extent  in  a  very  few  seconds.  It  is  ea.sy  to  comprehend  that  if  an  excess 
of  rubber  is  placed  over  the  teeth  upon  one  side,  and  heavy  pressure  is 
applied,  that  the  teeth  will  be  driven  into  the  plaster  encasement  and 
consequently  the  teeth  upon  that  side  of  the  denture  will  be  too  long. 
It  can  also  be  comprehended  that  if  the  cast  is  formed  of  regular  plas- 


VULCANIZERS. 


507 


ter,  and  excessive  rubber  and  pressure  be  applied  to  the  vault  of  the 
cast,  that  it  will  be  pressed  upward  and  the  plate  warped. 

We  shall  now  consider  the  power  of  the  press.  The  screw  is  a  combi- 
nation of  the  lever  and  wedge,  and  its  power  is  calculated  by  multiplying 
the  circumference  described  by  the  lever  by  the  pitch  of  the  screw. 
The  Buffalo  Dental  Manufacturing  Co.  No.  2  press,  Fig.  409,  has  a 
handle  eight  inches  long,  hence  describes  a  circumference  of  twenty-five 
plus  inches.  There  are  ten  threads  to  the  inch,  hence  a  pitch  of  one-tenth 
of  an  inch.  An  allowance  must  be  made  for  friction  in  the  screw,  but 
one-fifth  will  be  very  liberal,  when  we  shall  have  for  every  pound  of  force 
applied  at  the  end  of  the  handle,  two  hundred  pounds  pressure  under 
the  screw  or  a  ton  for  every  ten  pounds  of  force.  If  the  force  is  applied 
at  the  middle  of  the  handle  it  will  produce  one-half  as  much  pressure,  or 
a  ton  for  every  twenty  pounds  of  force.  It  is  now  easily  understood 
why  plates  are  warped,  and  these  heavy  malleable  iron  presses  are 
sometimes  broken.  The  student  should  now  return  to  the  Double 
Vulcanization  Process,  and  read  again  how  to  use  the  press. 

Fig.   471 


t^ 

^^^^o                           ^^^^ 

^ 

B 

c 

A 

-•"l''^^ 

\ 

11 

L.- 

Warming  oven. 

Flask  and  Rubber  Warming  Oven. — Fig.  471  shows  a  convenient 
arrangement  for  the  purpose.  It  consists  of  a  double  box,  12  inches 
wide  outside  and  9  inches  inside  measurement,  by  9  inches  outside  and 
6  inches  inside  in  heigth,  the  depth  of  the  oven,  (A),  may  be  12  inches. 
Thespace,  (B),an  inch  and  a  half  wide, is  partly  filled wdth  water,  (C). 
The  strips  of  rubber  to  be  used  in  packing  may  be  laid  on  the  top  to  be 
softened  while  the  flasks  are  heated  in  the  oven,  which,  as  will  be  seen 
by  the  illustration,  is  provided  with  a  door.  The  screw-cap,  (D),  is  for 
convenience  in  filHng  the  box  wdth  water,  and  is  provided  with  a  small 
hole  for  the  escape  of  steam.  The  box  should  be  made  of  copper  and 
may  be  heated  by  a  small  Bunsen  burner. 

Vulcanizers. — There  are  in  use  at  the  present  time  many  forms  of 
vulcanizers.  It  would  be  unnecessary  to  enumerate  them  all.  These 
descriptions  will,  therefore,  be  confined  to  some  of  the  best  and  sim- 
plest examples  of  the  somewhat  extensive  list. 


5U8 


VULCAMZED  RUBBER  AS  A  BASE. 


Cam-lock.— Tliis  is  one  of  the  new  cross-bar  vulcanizers.  It  is  very 
simple  in  construction  and  is  expeditious  to  liandle.  It  is  fitted  for 
either  gas  or  oil.     (Fig.  472.) 


Fig.  472 


C'aiii-iofk  vulcanizer. 


Edson. — This  is  an  older  form  of  screw-cap  vulcanizer.  It  has  n 
screw  press  within  the  boiler,  and  is  suitable  for  both  rubber  and  cel- 
luloid.    It  is  not  as  easy  to  handle  as  the  cross-bar  variety.      (Fig.  473.) 

The  Lewis  Cross-bar  Vulcanizer  (Fig.  474)  is  entirely  new  in  its 
essential  parts,^  and  embodies  many  valuable  improvements,  and  is 
probably  one  of  the  strongest,  safest,  and  most  convenient  vulcanizers 
of  the  cross-bar  pattern  in  use. 

The  boiler  is  hand-made  from  copper,  rolled  expressly  for  this  form 


SEA  BURY  VULCANIZER. 


509 


Fig.  473 


of  vulcanize!',  and  is  of  unusual  thickness.  The  cap  is  ribbed  on  the 
under  side  to  resist  any  strain  which  may  be  put  upon  it.  This  cap  has 
but  two  holes  drilled  in  it,  one  for  the  mercury  bath,  to  which  the  thei'- 
mometer  is  attached;  the  other  for  the  "manifold,"  which  carries  the 
safety-valve,  blow-off,  gas-regulator,  or  steam-gauge  (Fig.  475.)  The 
ring  surrounding  the  boiler  is  of  cast  steel,  and  is  therefore  of  ample 
strength.  Beside  the  lugs  for  taking  the  strain  off  the  cross-bar  and 
bolt,  it  has  a  dovetailed  projection  for  the  insertion  of  a  lifting  handle 
(Fig.  476.) 

It  will  be  observed  that  when 
the  cross-bar  and  cap  are  re- 
moved, there  are  no  swinging 
bolts  or  attachments  to  the  pot. 

The  cross-bar  is  of  an  im- 
proved form,  and  is  made  of 
cast  steel.  One  end  is  at  right 
angles  to  the  main  bar,  and  ter- 
minates in  projections  which 
catch  under  the  lugs  on  the 
ring.  Over  the  projections  is  a 
small  rib  which  prevents  the 
bar  from  dropping  out  of  posi- 
tion. The  other  end  of  the 
cross-bar  has  an  enlarged  por- 
tion for  the  reception  of  the  bolt, 
and  is  terminated  by  a  handle. 

The  vulcanizer  is  closed  by 
one  bolt  suspended  in  a  slot  on 
the  hand-end  of  the  cross-bar. 
The  bolt  is  squared  to  prevent 
rotation,  and  is  surrounded  by 
a  spring  for  the  purpose  of  dis- 
engaging it  from  the  lugs  when 
the  nut  is  loosened,  and  for  al- 
ways retaining  the  bolt  perpen- 
dicularly and  forcing  it  in  place 
automatically. 

The  vulcanizer  is  opened  by  loosening  the  nut  on  the  bolt  by  means 
of  the  wrench  furnished  for  the  purpose  (Fig.  477.)  The  bolt  will  be 
forced  downward  through  the  action  of  the  spring.  The  handle  of  the 
cross-bar  is  then  seized,  and  with  the  thumb  against  the  nut  it  is  pressed 
until  the  bottom  of  the  bolt  is  disengaged  from  the  lugs,  when  the  bar 
may  be  lifted  (Fig.  478.) 

The  Seabury  Vulcanizer. — This  apparatus  is  so  arranged  that  the 
vulcanizing  is  accomplished  with  dry  steam.  It  has  a  dry  chamber  or 
oven  for  vulcanizing,  which  is  distinct  from  the  steam-generating 
chamber  or  boiler,  the  two  being  connected  by  a  valve  cut-off.  The  vul- 
canizing chamber  has  a  capacity  of  three  flasks.     In  the  illustration  the 


Edson  vulcanizer 


510 


VULCAMZi:i)  RUBBER  AH  A  BASE. 
Fig.  474 


Lewis  cross-bar  vuJcanizer,  \\ith  gas  heating  apparatus. 
Fig.  475 


Manifold  with  safety  valve  and  blow-off. 
Fig.  476  -piG.  477 


Pot-lifter. 


Cross-bar  wrench. 


jacket  i.s  cut  away  to  show  the  relative  positions  of  the  two  chambers, 
and  their  connection.     It  is  claimed  for  this  machine  that  plates  made 


INSTRUCTIONS  FOR  USE  OF  TIME  REGULATORS.  511 

Fig.  478 


Removing  Lewis  cross-bar  from  pot. 
Fig.  479 


Seabury  vulcanizer. 


512 


VULCAXIZED  RUBBER  AS  A  BASE. 


in  it  are  as  stroiiti;  wlicii  only  lialf  as  tliick  as  those  vnleanized  in  the 
onhnary  way.     (Fig.  479.) 

Hy  eutting  oft"  the  steam  from  tlie  generating  ehamber,  eases  can  be 
removed  and  others  inserted  witliout  loss  of  time,  and,  as  the  plaster  is 
bnt  slightly  injured  l)y  the  dry  steam,  warjiing  of  plates  by  the  yielding 
of  the  investment  is  not  likely  to  occur. 

INSTRUCTIONS  FOR  THE  USE  OF  THE  TIME  REGULATOR. 

"The  gas  regulator  (Fig.  480)  is  secured  to  the  cap  by  means  of  the 
short  iron  pipe  or  coil.     This  is  screwed  into  a  hole  drilled  through  the 


Fig.  480 


Gas  regulator. 

cap  of  the  vulcanizer,  and  tapped  with  a  'one-eighth  gas-pipe  tap.'  If 
the  vulcanizer  has  a  'Lewis  manifold'  attached  to  the  cap  of  the  vulcan- 
izer, remove  the  screw  between  the  blow-off  and  safety-valve  and  screw 
the  coil-pipe  in  its  place.  After  the  gas  regulator  has  been  properly 
fitted,  place  the  vulcanizer  in  the  jacket  and  in  the  position  in  which  it 
is  to  be  used.  Connections  between  the  time  regulator,  gas  regulator, 
and  gas  burner  are  made  by  means  of  rubber  tubing.  The  engraving 
(Fig.  481)  illustrates  the  correct  method  of  connecting  gas  and  time  reg- 
ulators to  vnlcanizers.  Cut  a  piece  of  tubing  of  sufficient  length  to  reach 
from  the  gas-supply  tap  to  the  titne  regulator,  and  connect  them;  cut 
off  another  piece  to  reach  from  the  time  regulator  to  the  c/as  regulator. 


INSTRUCTIONS  FOR  USE  OF  TIME  REGULATORS. 


51^. 


and  attacli  to  the  gas  regulator  by  the  upright  or  straight  nipple  on 
top  of  the  No.  4  Lewis  gas  regulator;  then  conneet  the  downward 
curved  tube  of  the  gas  regulator  to  the  gas  burner  under  the  vulcan- 
izer  with  another  piece  of  rubber  tubing. 

"The  time  regulator  is  more  convenient  when  placed  on  a  bracket 
near  the  gas-supply  pipe.  It  is  then  out  of  the  way,  and  not  likely  to  be 
broken  from  contact  with  tools,  and  can  also  be  used  as  a  timepiece. 

To  Set  the  Time  Regulator. — When  the  valve  lever  on  top  of  the 
time  regulator  (Fig,  481)  is  engaged  with  the  screw  upon  the  minute  ar- 

Fig.  481 


No.  4  graduated  gas  regulator,  mounted  on  a  Lewis  cross-bar  vulcanizer. 


bor  on  the  back  of  the  clock,  the  valve  is  held  open  for  a  length  of  time 
depending  upon  whether  the  lever  is  engaged  with  the  first,  second,  or 
third  thread  of  the  screw;  and  the  lever  will  be  cast  off,  and  the  valve 
closed  when  the  minute-hand  reaches  the  figure  XII.  When  the  min- 
ute-hand is  at  IX  the  lever  will  be  cast  off  at  the  end  of  fifteen  minutes, 
if  it  is  engaged  with  the  first  thread  of  the  screw  from  the  end;  an  hour 
and  a  quarter,  if  engaged  with  the  second  thread,  and  so  on.     A  trial 

33 


)14 


VULCANIZED  RUBBER  AS  A  BASE. 


should  be  made,  and  the  time  ascertained  which  is  necessary  for  heat- 
ing the  vulcanizer  to  the  vulcanizing  point,  and  tiiis  time  should  be 
added  to  the  proposed  time  for  vulcanizing.  We  have,  therefore,  the 
following  : — 

"Rule. — Turn  the  minute-hand  to  as  many  minutes  before  the  hour 
as  the  number  of  odd  minutes  desired;  then  put  the  end  of  the  lever  in 
the  threads  of  the  screw  upon  the  minute  arbor  at  the  back  of  the  clock. 
The  jirsi  thread  from  the  end  gives  the  odd  minutes  to  which  the  clock 
is  set;  the  next  and  each  succeeding  ^hread  gives  a  full  hour.  For  ex- 
ample: For  an  hour  and  twenty  minutes,  set  the  minute-hand  at  the 
figure  VIII,  and  engage  the  lever  in  the  second  thread  from  the  end  of 
the  screw.  At  the  end  of  that  time  the  lever  will  disengage  and 
automatically  shut  off  the  gas  from  the  vulcanizer.  If  this  w^ere  to  l)e 
an  hour  longer — l.  e.,  two  hours  and  twenty  minutes — the  lever  should 
be  placed  on  the  third  thread  of  the  screw.  For  three  hours,  set  the 
minute  hand  at  XII  and  the  hour  in  the  third  thread  of  the  screw  lever. 

"Those  who  use  vulcanizers  should  be  thoroughly  informed  as  to  the 
nature  and  properties  of  steam.  The  fact  should  be  borne  in  mind 
that  a  vulcanizer  is  subject  to  the  same  laws  and  conditions  as  a  steam 
boiler,  which  it  is  in  fact,  and,  although  it  is  comparatively  safe  and 
easily  operated,  it  may,  by  carelessness  or  ignorance  in  its  management, 
become  exceedingly  dangerous. 

"The  following  table  of  steam-pressure  will  be  found  convenient  for 
reference,  as  it  has  been  corrected  so  that  it  shows  the  true  temperature 
for  any  pressure  indicated  by  the  steam-gauge.  Fractions  are  omitted, 
and  the  nearest  whole  number  is  used  instead.  The  French  table  gener- 
ally used  shows  14.7  pounds  pressure  at  212°,  whereas  the  steam-gauge 
at  that  temperature  will  indicate  0,  unless  by  the  expansion  of  heated 
air  confined  in  the  vulcanizer.  The  guage  is  therefore  just  one  atmos- 
phere lower  than  French  table: 

Table  of  the  Elastic  Force  of  Steam}  (corrected  to  correspond  with  the 

steam-gauge)  • 


Degrees  of  temperature, 

Elastic  force  in  lbs. 

Degrees  of  temperature, 

Elastic  force  in  lbs 

Fahrenheit. 

per  square  inch. 

Fahrenheit. 

per  square  inch. 

212  ...    . 

.   .    .    .      0 

390 

...  205 

220  ...    . 

.    .    .    .      2 

400 

.    .    .  234 

230  ...    . 

.    .    .    .      6 

410 

...  264 

240  ..    . 

.    .    .    .    10 

420 

.    .  296 

250  .... 

.    .    .    .    15 

430  ....    . 
440 

335 

260  ...    . 

.    ...    21 

.    .    .375 

270  ...    . 

.    ...    27 

i50 

.    .    .415 

280  ...    . 

.    ...    34 

460 

...  455 

290  ...    . 

.    ...    43 

470 

.    .    .515 

300  ...    . 

.    ...    52 
.    ...    63 

480 

.    .      565 

310.    ..    . 

490 

...  603 

320  ...    . 

.    ...    75 

500 

.   .    .663 

330  ...    . 

.    ...    89 

510 

...  721 

340  ...    . 

.    ...  104 

520 

...  793 

350  ...    . 

.    ...  120 

530 

.    .    .  864 

360  ...   . 

.    ...  140 

540 

.    .    .937 

370  ...    . 

.    .    .    .  IGO 

550 

.    .    1015 

380.   ..   . 

.    ...  180 

*. General  instructions  for  operating  dental  \TiIcanizers,  Buffalo  Dental  Manf'g  Co.,  July,  1898 


INSTRUCTIONS  FOR  USE  OF  TIME  REGULATORS.  515 

"It  will  be  noticed  that  as  the  temperature  rises  the  pressure  of  steam 
increases  in  a  constantly  increasing  ratio  for  equal  increments  of  heat, 
the  pressure  being  nearly  doubled  by  the  addition  of  fifty  degrees  to 
the  temperature.  This  fact  will  show  the  necessity  of  care  and  watch- 
fulness while  vulcanizing. 

"The  bulb  of  the  thermometer  is  set  in  a  mercury  bath.  This  is  the 
small  cup,  forming  a  part  of  the  vulcanizer  cap,  to  which  the  thermom- 
eter case  is  screwed.  This  cup  should  contain  sufficient  mercury  to 
ensure  its  touching  the  bulb  of  the  tube  when  the  thermometer  case  is 
screwed  down  properly.  This  makes  a  metallic  connection  between  the 
thermometer  bulb  and  the  vulcanizer  cap,  and  is  absolutely  necessary 
for  the  proper  indication  of  heat  by  the  thermometer. 

"Should  the  mercury  column  separate,  it  can  usually  be  reunited  by 
removing  the  tube  from  the  thermometer  case,  holding  it  perpendicu- 
larly, and  striking  the  bulb  with  some  force  upon  the  palm  of  the  hand, 
or  by  holding  the  tube  by  the  bulb  and  giving  it  a  sudden  flirt.  If  the 
vulcanizer  is  used  with  the  thermometer  in  this  condition,  it  should  be 
remembered  that  it  is  the  whole  column  that  denotes  the  heat,  and  allow- 
ance should  be  made  for  the  broken  part;  i.  e.,  if  there  is  enough  mer- 
cury separated  to  fill  the  space  of  ten  degrees,  the  remainder  of  the  col- 
umn should  only  rise  to  ten  degrees  less  than  the  temperature  desired. 

"Directions  for  inserting  a  new  tube  in  the  thermometer  case  will 
generally  be  found  on  the  package  containing  the  tube  and  scale. 

"Thermometers  are  accurately  marked,  by  test  instruments,  at  the 
212°  and  320°  points,  and  the  scales  are  especially  graduated  for  each 
tube,  as  the  positions  ofthe  points  above  named  vary  in  different  tubes. 
Each  tube  must,  therefore,  be  used  with  its  own  scale,  and  in  fitting  it  to 
the  case,  care  should  be  taken  that  the  black  mark  on  the  tube  indicating 
the  320°  point  is  brought  exactly  opposite  to  the  320°  point  on  the  scale. 

"The  thermometer  does  not  always  give  a  correct  indication  of  the 
heat  of  the  vulcanizer.  It  only  gives  the  temperature  of  the  vulcanizer 
top,  which  may  not  be  that  of  the  flask.  In  fact,  the  indications  of  the 
thermometers  employed  on  vulcanizers  are  almost  invariably  too  low, 
owing  to  imperfect  conduction  of  heat,  radiation,  etc.;  and  the  vulcan- 
zation  temperature,  instead  of  being  320°,  as  indicated,  is  more  usually 
330°  to  340°." 

The  plan  of  providing  a  mercury  bath  for  the  reception  of  the  bulb 
is  a  great  improvement  over  the  old  way,  and  prevents  the  fracture  of 
the  bulb  by  the  great  pressure  of  the  steam,  which  was  of  such  frequent 
occurrence  w^hen  the  thermometer  was  in  direct  contact  with  the  latter. 

Damage  to  the  glass  bulb  of  the  thermometer  is  manifested  by  a  rise 
in  the  mercury,  which  cannot  be  brought  down  to  the  usual  vulcanizing 
point  by  turning  off  the  flame  of  the  burner;  consequently  the  ther- 
mometer ceases  to  correctly  indicate  the  degree  of  heat,  and  imperfect 
vulcanization  is  the  result.  Leakage  of  steam  around  the  packing  of 
the  vulcanizer  should  also  be  guarded  against,  as  in  such  cases  all  of  the 
water  may  escape  from  the  apparatus  before  the  vulcanizing  is  complete. 
Loss  of  all  of  the  water  in  the  vulcanizer  may  be  detected  by  a  per- 


Fig.   ls3 


Flask-tongs, 


Vulcanite  files. 


TRIMMERS 


517 


Fig.  484 


? 


Fig.  485 


\L 


Wilson  .set. 


Spaulding  trimmer, 

sistent  fall  of  the  mercury,  even  when  the  gas  flame  is  greatly  increased, 
and  when  this  phenomenon  is  observed,  the  gas  should  be  turned  ott, 
the  vulcanizer  allow  to  cool,  and  new  packmg  adjusted. 


518 


VULCAXIZED  RUBBER  AS  A  BASE. 


Failure  to  strictly  observe  this  rule  has  undoubtedly  resulted  in  many 
serious  accidents.  An  example  of  this  kind  occurred  some  years  since 
in  the  laboratory  of  the  Dental  Department  of  the  University  of  Pennsyl- 
vania. A  student  was  endeavoring  to  vulcanize  with  an  apparatus 
whicli  leaked  at  the  packing:  noticing  that  the  mercury  persisted  in 
falling,  he  continued  to  increase  the  gas  fiame  until  the  lower  part  of  the 
vulcanizer  was  probably  red  hot.  While  he  stood  before  it,  holding 
a  lighted  match  to  the  tube  to  enable  him  to  see  the  column  of  mercury, 
the  vulcanizer  exploded  with  terrific  force,  sending  the  top  through  the 
ceiling  and  pieces  of  the  boiler  in  every  direction.  It  is  quite  likely 
that  in  this  particular  case  the  steam  was  partly  decomposed  by  con- 
tact with  the  hot  metal,  producing  a  highly  explosive  com})ination  of 
oxygen  and  hydrogen:  no  other  theory  would  seem  to  account  for  the 
great  force  of  the  explosion. 


Fig.  486 


Ivory  Scrapers. 

Vulcanizing. — The  flask  or  flasks  are  placed  in 
the  vulcanizer  and  filled  about  three-quarters  with 
clean  water.  The  packing  should  be  without  a 
break  in  its  continuity,  otherwise  the  steam  will 
escape;  the  joint  between  the  pot  and  cover  must  be 
protected  from  adhesion  by  slightly  coating  it  with 
black  lead  or  soap-stone.  The  cover  is  then  put  on, 
but  the  valve  is  not  closed  until  the  heated  air 
which  precedes  the  generation  of  steam  has  escaped; 
the  valve  is  then  closed.  A  close  watch  must  be 
kept  on  the  thermometer  or  gauge  until  the  vul- 
canizing point  is  reached  unless  a  time  regulator  is 
used. 

Flask-tongs, — Figs,  482  shows  a  useful  form  of  flask-tongs  for  lifting 
flasks  from  the  vulcanizer.  They  are  made  of  sufficient  length  to 
reach  the  bottom  of  a  three-case  vulcanizer,  and  will  securely  grip  the 
flask 


OCCASIONAL  AiYD  SPECIAL  METHODS. 


519 


Files. — Fig.  483  illustrates  some  excellent  forms. 

Scrapers. — There  are  a  great  variety  of  scrapers  and  chisels  from 
which  each  operator  may  select  such  as  seem  best  adapted  to  his  hand. 
The  writer's  preferences  are  the  ones  here  illustrated. 


Fig.  487 


fejl 


Kingsley  scrapers. 


OCCASIONAL  AND  SPECIAL  METHODS. 


Gum  Section  Teeth. — There  are  two  varieties  of  teeth  used 
for  the  vulcanite  base.  They  are  known  as  plain  and  gum 
section  teeth.  The  plain  teeth  are  single  and  have  no  porce- 
lain gum,  but  may  have  a  reproduction  of  the  neck  portion 
of  the  root  of  the  tooth.  The  gum  sections  may  be  single 
teeth  with  a  porcelain  gum,  but  usually  they  are  in  the  form 
of  blocks,  each  containing  two  or  three  teeth.  There  are 
various  combinations  of  the  teeth  in  the  blocks  designed  to 
meet  special  cases.  The  plain  teeth  are  used  only  for 
the  double  and  single  vulcanization  methods  as  previously 
described,  but  either  plainer  section  teeth  may  be  used  for 
the  single  vulcanization  sub-method.  The  gum  section  teeth 
require  much  grinding  to  adapt  them  to  the  wax  or  hard 
gum  base-plate.  The  joints  between  the  blocks  must  be 
ground  to  fit  squarely  against  each  other  and  not  with  a  V- 
shaped  space.  The  case  should  be  flasked  at  the  periphery 
of  the  wax.  Much  care  should  be  used  in  packing  and 
closing  the  flask.  Do  not  use  too  great  pressure,  as  there 
is  danger  of  checking  the  porcelain  gum  and  of  opening  the 
joints. 
Advantages  and  Disadvantages  of  Section  Teeth. — Where  the  gum 
portion  must  be  restored  and  there  is  extreme  mobility  of  the  Hp,  the 
porcelain  gum  will  appear  to  better  advantage  than  the  vulcanite  gum 


020  VULCANIZED  RUBBER  AS  A  BASE. 

restoration.  In  partial  cases,  blocks  of  one  to  four  teeth  can  sometimes 
be  used  to  very  great  advantage. 

The  disadvantages  are:  (1)  the  forms  of  the  sections  preclude  the 
possibility  of  the  individualizing  of  the  teeth  by  the  dentist,  they  always 
have  a  stiff,  unnatural  appearance;  and  (2)  there  is  a  space  between 
the  porcelain  and  vulcanite  for  the  accumulation  of  filth.  This  last 
objection  does  not  apply  to  most  of  the  oartial  cases  requiring  gum 
section  teeth,  because  in  these  cases  the  gum  portion  is  not  backed  up 
with  vulcanite.  Some  years  ago  the  gum  section  teeth  were  in  al- 
most universal  use,  but  to-day  there  are  sections  of  the  country  in 
which  sets  of  fourteen  gum  section  teeth  are  rarely  used.^ 

Plain  Teeth  Without  Gum  Restoration. — Many  cases  of  recent  ex- 
traction antl  in  a  few  cases  where  tlie  gum  is  sufficiently  full  after  re- 
sorption has  taken  place,  no  restoration  of  the  gum  is  required.  In  these 
cases  the  plaster  of  the  cast  is  scraped  away  one  thirty-second  of 
an  inch  for  the  insertion  of  the  cervical  end  of  the  teeth.  Without  this 
precaution  the  teeth  in  the  finished  denture  would  not  set  closely  nor 
appear  to  grow  from  the  gum. 

Black  Rubber  Single  Vulcanization  Method. — Some  people  fear  the 
effect  of  the  coloring  matter  in  red  rubber,  so  that  it  may  be  desir- 
able to  construct  the  denture  of  black  rubber,  when  it  becomes  very 
necessary  that  the  black  rubber  should  not  show  upon  the  labial  and 
buccal  surfaces.  The  two  rubbers  can  be  packed  in  the  usual  way  or  by 
this  very  ingenious  method." 

Dr.  Slabaugh's  Method.  — "After  separating  the  flask  and  boihng 
out  the  wax,  I  coat  the  cast  w'ith  silex  and  then  lay  on  my  black  or  red 
rubber  loosely  over  the  cast.  I  then  take  a  piece  of  the  cloth  that  comes 
on  the  sheets  of  rubber  and  lay  it  over  the  rubber  that  is  on  the  cast,  and 
place  the  two  parts  of  the  flask  together  and  set  them  in  boiling  water 
for  a  few  minutes,  after  which  I  place  the  flask  in  a  press  and  force  it 
together,  care  being  taken  to  have  the  flask  entirely  together.  The 
flask  is  entirely  filled  with  the  rubber.  -I  now  separate  the  flask  and 
the  rubber  will  adhere  to  the  cast.  Remove  the  cloth  that  has  been 
put  on  and  you  will  have  perfect  imprints  of  the  teeth  and  pins  in  the 
rubber  that  have  l)een  made  through  the  cloth.  I  then  place  a  narrow 
strip  of  pink  rubber  on  the  black  or  red  over  the  imprints  of  the  teeth 
and  up  to  about  one  thirty-second  of  an  inch  of  the  imprint  of  the  pins. 
Place  the  two  parts  of  the  flask  together  and  force  them  down  and  it  is 
ready  for  the  vulcanizer.  Cut  waste  gates  only  in  the  rear  so  that  when 
the  flask  is  closed  the  second  time  with  the  little  piece  of  pink  rubber 
added  to  it,  the  slight  displacement  of  black  or  red  rubber  will  be  en- 
tirely toward  the  rear." 

Waxable  Rubber — Recently  this  material  has  been  placed  before 
the  profession  by  John  Hood  &  Co.,  Boston.  Its  physical  properties 
are  very  much  like  those  of  sheet  gutta-percha.     It  is  not  a  patented 

'The  writer  has  put  up  but  one  set  of  gum  section  teetli  in  nineteen  years. 
2  Dr.  Frank  W.  Slabaugh  of  Omaha,  Xeb. 


REMOVING  THE  TEETH  FROM  A  VULCANITE  PLATE.  521 

article.  The  claims  for  the  material  and  the  method  of  construction 
are  given  as  follows:  "An  entirely  new  process  with  a  material  far  sup- 
erior to  rubber,— much  lighter  and  one  that  will  not  become  slimy  in  the 
mouth.  To  use,  hold  a  sheet  over  the  burner  the  same  as  a  sheet  of 
wax  and  make  a  trial  plate;  build  out  with  rubber  to  the  desired  fulness 
and  put  the  teeth  in  place  with  a  spatula,  by  keeping  the  rubber  soft  and 
heating  the  tooth.  Use  the  rubber  just  as  you  do  wax,  and  smooth  it  be- 
fore adding  pink  rubber.  After  it  is  cool,  add  the  pink  rubber  by  first 
removing  the  teeth  without  heating,  leaving  the  impression  of  the  teeth 
in  the  rubber.  Cut  a  strip  of  pink  rubber  wide  enough  to  reach  the  ridge 
and  cover  the  indentations  of  the  teeth,  just  above  the  pin  holes,  and 
to  reach  from -heel  to  heel.  Soften  the  rubber  slightly  and  heat  the 
tooth  and  replace  it,  carrying  the  pink  rubber  under  the  neck  of  the 
tooth.  In  this  manner  you  can  make  a  natural  festoon  as  full  as  is  de- 
sired. Care  should  be  taken  not  to  make  any  finger-nail  marks  or  to 
mar  the  pink  rubber.  After  the  teeth  have  been  tried  in,  before  placing 
on  the  cast,  paint  the  cast  with  the  solution  and  heat  the  plate,  pressing 
it  in  place  with  the  fingers.  Smooth  the  red  rubber  by  the  use  of  chlo- 
roform on  a  cloth.  Moisten  the  cast  and  drive  the  air  from  it.  Fill  the 
flask  with  plaster  and  press  in  cast,  shaking  the  flask  well  to  prevent 
bubbles.  Vulcanize,  taking  twenty-five  minutes  to  run  up,  and  then 
hold  it  one  hour  at  315  degrees." 

Thick  Vulcanite.  — Thick  masses  of  rubber  may  be  vulcanized  by 
gradually  increasing  the  heat  from  280°  F.  to  300°  F.  (See  "History  of 
Vulcanite"  in  the  early  part  of  this  chapter.)  Another  method  is  to  fill 
the  mold  with  vulcanite,  having  the  rubber  packed  about  it;  or  the  mold 
may  be  largely  filled  with  pink  rubber. 

REMOVING  THE  TEETH  FROM  A  VULCANITE  PLATE. 

Sheet  Iron  Method. — Place  the  denture,  teeth  downward,  upon  the 
sheet  iron  over  a  gas  stove,  and  when  the  vulcanite  is  thoroughly 
softened,  the  teeth  may  be  pushed  off  one  at  a  time  by  inserting  the  wax 
spatula  between  the  tooth  and  the  vulcanite  upon  the  lingual  side.  The 
plate  is  held  by  a  pair  of  pliers  and  the  dislodged  teeth  are  permitted  to 
fall  upon  wood,  or  better,  upon  cloth,  but  not  upon  cold  iron  or  stone. 
Any  portion  of  the  vulcanite  remaining  about  the  pins  should  be  re- 
moved. If  necessary,  these  small  portions  of  vulcanite  may  be 
softened  by  grasping  the  tooth  in  a  pair  of  solder  tweezers  and  holding 
in  the  Bunsen  flame. 

Glycerine  Method — The  denture  is  placed  in  a  vessel  of  glycerine 
and  heated  to  the  boiling  point  of  the  liquid,  when  the  teeth  can  be  re- 
moved as  in  the  other  method.  The  glycerine  is  soluble  in  water  and 
easily  removed.  The  fumes  of  the  heated  glycerine  are  more  ob- 
jectionable to  some  than  those  of  the  overheated  rubber. 

Flame  Method — The  denture  is  grasped  with  a  pair  of  pliers  and 
the  outer  surface  of  the  teeth  heated  by  passing  repeatedly  through  the 


522 


VULCAXIZEI)  RUBBER  AS  A  BASE. 


flame  until  the  vulcanite  is  softened  about  the  pins,  when  they  are  re- 
moved as  before  described. 

It  is  not  advisable  to  remove  the  teeth  b}  heat  from  a  denture  which 
is  to  be  used  again,  because  of  the  liability  of  warping  the  plate.  The 
vulcanite  should  be  cut  from  about  the  pins  of  the  tooth  with  a  bur  in 
the  engine  or  with  a  chisel. 

Partial  Cases. — It  frequently  occurs  in  constructing  partial  artificial 
dentures  for  the  replacement  of  single  incisors  or  canines  that  the  ordi- 
nary rubber  teeth  are  too  thick  to  admit  of  their  being  arranged  to  con- 
form to  the  line  of  the  natural  teeth  without  interfering  with  the  normal 


Fig.  488 


Partial  vulcanite  plate  arranged  for  case  with  marked  overbite. 

occlusion  (Fig.  488).  In  such  cases  a  plate  tooth  may  be  used,  and  is 
attached  by  means  of  gold  backings,  bent  at  an  angle  with  the  base  of 
the  tooth,  of  sufficient  length  to  allow  of  the  projecting  portion  to  be 
imbedded  in  the  rubber  plate,  as  shown  in  Figs.  488  and  489.  The  ex- 
tension of  the  gold  backing  shown  in  Fig.  489  has  two  or  more  holes 
punched  and  countersunk  in  it,  so  as  to  be  held  firmly  by  the  vulcanized 
rubber. 

Fig.  492 


Fig.  489 


Fig.  490 


Fig.  491 


Tooth  and  clasps  prepared  for  attachment  to  vulcanite  plate. 


Gold  Clasps. — Gold  clasps,  when  used  in  combination  with  rubber, 
are  attached  in  the  same  way.  The  clasp,  after  being  accurately  fitted 
to  the  plaster  tooth,  is  provided  with  a  piece  of  gold  plate  soldered  at  a 
point  next  to  the  rubber  plate  (Figs.  490-492).  This  attachment 
should  be  slightly  raised  from  the  cast,  so  that  it  will  be  entirely  en- 
veloped by  the  rubber,  as  shown  in  Fig.  490. 


PARTIAL  LOWER  DENTURES. 


523 


There  is  some  danger  of  these  chxsps  being  forced  sHghtly  from  their 
correct  position  by  the  pressure  of  the  rubber  in  packing.  This  difficulty 
may  be  entirely  overcome  by  soldering  a  temporary  support  of  scrap 
gold  to  the  clasp  and  bending  it  over  the  plaster  tooth,  as  shown  by 
Fig.  492.  Usually  this  device  will  be  found  effective  in  retaining  the 
clasp  in  contact  with  the  tooth.  After  vulcanizing,  the  supporting 
piece  of  gold  may  be  sawed  off  with  a  jeweler's  saw.  In  packing  a  case 
arranged  with  gold  clasps,  a  thin  sheet  of  rubber  should  be  worked  un- 
der the  gold  attachment  to  further  protect  the  latter  from  displace- 
ment. It  will,  of  course,  be  understood  that  the  clasps  are  to  remain  in 
position  during  the  packing;  therefore,  in  flasking  such  cases  the  plas- 
ter should  be  made  to  cover  the  portion  of  the  clasp  not  actually  in  con- 
tact with  the  rubber;  this  affords  additional  support  to  the  clasp  during 
the  pressure  accompanying  the  closing  of  the  flask  in  packing,  and  will 
keep  it  in  correct  relation  to  the  plaster  tooth. 

Partial  Lower  Vulcanite  Dentures. — Gold  is  used  in  combination 
with  that  class  of  partial  lower  dentures  designed  to  replace  the  bicus- 


FiG.  493 


Fig.  494 


Strengthener  of  clasp  gold  to  be  used  in  connection       Strengthener  and  clasps  for  lower  plate, 
with  vulcanite. 


pids  and  molars  and  when  the  natural  incisors  and  canines  remain.  For 
the  purpose  of  strengthening  the  piece  and  to  lessen  its  bulk  in  front  a 
plate  of  gold  is  sometimes  swaged  to  fit  the  cast  back  of  the  front  teeth, 
and  where  the  ridge  is  not  well  defined  and  not  favorable  to  the  reten- 
tion of  the  piece  without  some  form  of  attachments,  gold  clasps  are 
soldered.  The  gold  plate  is  allowed  to  extend  somewhat  beyond  the 
canine  teeth;  the  ends  are  perforated  by  the  punching  forceps,  as  shown 
by  Fig.  493,  to  ensure  strong  union  with  the  rubber.  This  plate  is  then 
put  upon  the  cast  and  secured  in  place  by  means  of  wax;  the  teeth 
are  arranged  in  position,  waxed  up,  and  vulcanized  in  the  usual  way. 
The  denture  when  finished  presents  to  view  a  plate  with  the  anterior 
part  of  gold,  while  the  two  parts  holding  the  teeth  and  resting  upon  the 
ridge  on  each  side  are  of  vulcanite.  The  purpose  of  such  a  combination 
is  to  save  labor  and  material,  but  a  denture  so  constructed,  while  better 
in  point  of  durability  and  because  of  the  absence  of  bulkiness  where  it 


524 


VULCAXIZKl)  RUBBER  AS  A  BASE 


passes  around  back  of  the  incisors  and  canines  than  vulcanite  alone,  is 
still  far  inferior  to  one  constructed  entirely  of  gold,  for  while  such  a  den- 
ture is  doubtless  strono;or  than  one  of  vulcanite  alone,  it  is  not  so  durable 
as  one  made  exclusively  of  gold,  on  account  of  the  liability  of  the  piece 
to  break  at  the  points  where  the  gold  is  imbedded  in  the  vulcanite. 
Dentures  of  the  class  above  referred  to  should  always  be  made  entirely 
of  metal,  and  the  expenditure  of  money  and  labor  is  but  little  greater 
than  in  the  combination  plan,  while  the  general  result  is  in  every  way 
more  satisfactory. 

Dr.  P.  T.  Dashwood  uses  in  place  of  the  swaged  plate  above  sug- 
gested for  the  anterior  portion  of  lower  partial  dentures,  an  iridio- 
platinum  wire,  gauge  14,  which  is  bent  with  round  nosed  pliers  to 
conform  to  the  lingual  alveolar  surface.  The  ends  are  flattened  upon 
an  anvil  and  cross  pieces  of  platinous  gold  are  soldered  to  them  for  the 
attachment  of  the  vulcanite.  He  makes  the  just  claims  that  the  wire 
is  "stronger  than  vulcanite,  is  nuich  more  comfortable  to  the  patient, 
and  is  more  hvgienic. 

Fig.   4'.>r, 


Completed  plate. 

Natural  Teeth  upon  Vulcanite  Base. — "Where  the  anterior  natural 
teeth  have  become  so  loosened  by  the  ravages  of  pyorrhoea  alveolaris,  by 
excessive  resorption  of  the  gums  and  sockets  or  of  the  roots  of  the  teeth, 
so  that  their  complete  loss  is  a  matter  of  a  very  short  period  of  time,  a 
plaster  impression  may  be  taken  of  the  mouth  before  the  removal  of 
the  loose  teeth. 

In  constructing  partial  dentures  for  cases  where  the  natural  organs 
are  prematurely  lost,  it  is  much  the  better  practice  to  reset  the  natural 
teeth,  provided,  as  is  often  the  case,  they  are  of  dense  structure  and 
have  not  previously  been  attacked  by  caries.  This  is  done  by  making 
a  plate  in  the  usual  way,  and  in  the  spaces  to  be  occupied  by  the  natural 
teeth  vulcanizing  a  strong  platinous  gold  wire,  being  careful  to  place 
the  gold  pin  in  the  centre  of  the  space.  The  wire  must  have  an  at- 
tachment soldered  to  it,  so  that  its  connection  with  the  rubber  will  be 
secure.     The  wire  may  be  arranged  with  a  simple  piece  of  scrap  gold 


NATURAL   TEETH  UPOX   VULCANITE  BASE. 


525 


soldered  to  the  end  to  be  imbedded  in  tlie  rubber,  as  shown  in  Fig.  496, 
or  it  may  be  provided  with  a  perforatefl  extension,  as  shown  in  Fig. 
497,  by  whicli  union  with  the  rubber  may  be  secured  and  great  bulki- 
ness  avoided.  The  rubber  portion  of  the  denture  finished,  it  only  re- 
mains to  remove  the  infirm  natural  organs  and  attach  them  to  the  plate 
made  ready  for  their  reception.  This  is  done  by  sawing  oft"  the  roots 
(Fig,  496),  enlarging  the  pulp-canal  witli  a  suital)le  engine  drill,  fitting 

Fig.  496 


Cast  with  plate  in  position    natural  tooth  to  be  added. 


the  neck  of  the  tooth  to  the  plate,  and  into  the  socket,  as  shown  in  same 
figures,  and  then  attaching  the  tooth  to  the  pin  (Fig.  497)  and  plate  by 
means  of  zinc-phosphate  cement,  being  careful  to  dry  the  parts  thor- 
oughly before  the  cement  is  applied.  This  method  of  resetting  natural 
teeth  is  more  conveniently  done  on  gold  plates  than  on  those  of  rubber, 
but  it  is  applicable  to  both.     It  possesses  the  following  advantages: 


Fig.  497 


Natural  tooth  mounted  upon  plate. 

First.  The  teeth  are  the  patient's  natural  teeth,  and  this  fact  very 
greatly  lessens  the  repugnance  which  many  individuals  of  exalted  sen- 
sibilities feel  to  artificial  teeth.  Second.  It  saves  the  individual  from 
being  seen  without  teeth — a  matter  of  the  greatest  importance  to  many 
patients.  Third.  Artificial  appearance  is  avoided,  for  they  are  the 
natural  teeth  of  the  patient,  and  nothing  more  need  be  said  on  the  score 
of  natural  effect.  The  question  is  often  asked.  Do  teeth  reset  in  this 
manner  suffer  from  dental  caries  ?    It  has  been  observed  that  such  teeth 


526  VULCAXIZED  RUBHEIi  AS  A  BASE. 

are  not  more  liable  to  decay  after  their  attachment  to  a  plate  than  they 
were  before  removal  from  their  sockets. 

If  the  infirm  natural  teeth  are  of  poor  (juality  and  have  large  fillings 
in  them,  it  is  better  to  use  porcelain  teeth,  and  the  dentures  can  be  en- 
tirely finished  ready  for  insertion  before  the  natural  teeth  need  be  ex- 
tracted. Care  should  be  observed  to  allow  the  necks  of  the  artificial 
teeth  to  extend  well  into  the  sockets  of  the  extracted  organs,  to  anticipate 
resorption  of  the  parts  which  to  some  extent  is  sure  to  occur  at  such 
points. 

Combination  Dentures. — Under  this  heading  are  included  metal 
plates  with  vulcanite  attachments,  vulcanite  plates  with  metal  linings, 
vidcanite  dentures  strengthened  with  perforated  metal  plates,  etc.  Ex- 
cellent results  may  be  obtained  by  attaching  the  teeth  to  metallic  plates 
by  means  of  vulcanized  rubber.  A  denture  so  constructed  will  be 
found  to  possess  greater  strength  than  one  of  vulcanite  alone,  while  it 
will  have  the  additional  advantage  of  being  free  from  interstices,  which 
favor  the  lodgment  of  decomposable  debris.  In  other  words,  the  com- 
bination of  metal  plate  with  vulcanite  attachment  thoroughly  meets  the 
objections  raised  against  either  method  alone. 

Either  gold,  silver,  platinum,  aluminum,  or  any  of  their  alloys  usually 
employed  in  prosthetic  dentistry,  may  be  used  in  the  construction  of  one 
of  these  combination  dentures;  preference,  however,  should  be  given 
to  gold  as  a  base.  Platinum  unalloyed  is  not  well  adapted  for  the  pur- 
pose, on  account  of  its  great  ductility  and  weight,  but  when  alloyed  with 
a  small  percentage  of  iridium  its  rigidity  is  so  much  increased  that  a 
plate  of  No.  29  thickness  will  be  found  to  be  cjuite  as  strong  as  a  much 
thicker  plate  of  18-carat  gold. 

Either  ordinary  silver  plate  of  standard  ^  fineness  may  be  used  with 
rubber  attachment,  or  silver  alloyed  with  platinum,  the  latter  having 
greater  tensile  strength  than  the  former.  It  must  be  remembered,  how- 
ever, that  silver  has  a  powerful  affinity  for  sulphur,  the  indurating  agent 
in  vulcanite,  and  that  the  presence  of  platinum  as  an  alloy  does  not  en- 
tirely protect  the  silver  from  the  action  of  the  sulphur.  It  is,  therefore, 
necessary,  where  a  silver  plate  is  used,  to  interpose  a  layer  of  No.  60 
tin-foil  between  the  rubber  and  the  plate;  this  precaution,  however,  is 
not  necessary  where  celluloid  is  used. 

In  silver  dentures  with  vulcanite  attachments  the  anchorages  must 
invariably  be  made  of  platinum  or  gold  w^ire.  After  the  plaster  wall  is 
made  and  the  wax  removed  from  around  the  teeth,  the  exact  positions 
of  the  anchorages  are  marked  upon  the  plate  with  a  sharp  steel  point  to 
the  number  of  eight  or  ten.  The  plate  is  then  laid  on  a  charcoal  support 
and  pieces  of  silver  solder  are  fused  at  the  points  indicated.  The  wire 
is  then  cut  into  proper  lengths,  screwed  in  a  vise,  and  one  end  of  each 
flattened  by  means  of  a  rivetting  hammer  into  the  form  of  a  head :  each 
pin  is  then  taken  up  separately,  the  headed  end  dipped  in  borax,  and 
placed  on  the  plate  at  a  point  where  a  piece  of  solder  has  been  fused. 
The  borax  will  assist  in  retaining  the  piece  of  wire  until  the  flame  of  the 

^Coin. 


VULCAXITE  WITH  PLATE  OF  FUSIBLE  ALLOY.  Tyll 

blowpipe  is  directed  upon  it  to  remelt  the  solder  and  unite  the  pin  to 
the  plate.  The  wire  anchorages  are  not  to  be  bent  into  hook  form,  as 
shown  in  Fig.  500,  until  after  the  tin-foil  protection  has  been  adjusted. 
The  pins  are  forced  through  the  tin-foil  and  pressed  with  a  rubber  point 
and  burnished  closely  to  the  plate.  The  holes  made  by  the  passage  of 
the  pins  through  the  tin-foil,  if  care  is  used,  will  not  be  large  enough  to 
allow  the  rubber  to  reach  the  silver  to  any  great  extent.  After  the  tin 
is  in  place  the  pins  may  be  bent  with  pliers,  as  shown  in  Fig.  500. 

Another  method  is  by  directly  tinning  the  surface  to  be  covered  by 
the  rubber.  The  silver  is  cleansed  and  covered  with  a  saturated  solu- 
tion of  zinc  chloride.  The  tin-foil  is  pressed  carefully  against  the  silver 
and  the  plate  is  held  above  a  Bunsen  flame  until  the  tin  fuses.  Its 
flowing  is  to  be  directed  by  means  of  a  camel's-hair  pencil  which  has 
been  dipped  in  the  zinc  solution. 

Vulcanite  in  Combination  with  Plates  of  Fusible  Alloy. — For  the 
modus  operandi  of  the  preparation  of  plates  of  fusible  alloys  the  reader 
is  referred  to  Chapter  XY.  The  Reese  or  AYeston  fusible  alloys  can 
be  cast  very  thin,  and  yet  are  sufficiently  rigid  to  withstand  the  force  of 
mastication.  These  alloys  retain  their  color  and  make  an  admirable 
combination  plate.  Having  finished  the  plates  as  shown  above,  the 
edges  and  raised  rims  are  trimmed  to  the  desired  dimensions.  A  roll 
of  softened  modelling  compound  or  wax  is  pressed  around  the  gums 
over  the  alveolar  ridges,  and  trimmed  with  a  knife  to  the  supposed 
height  of  the  teeth.  The  plates  are  then  tried  in  the  mouth,  and  the 
wax  trimmed  from  all  sides  until  perfect  occlusion  and  contour  are 
obtained.  The  median  line  is  marked  on  the  modelling  compound  or 
wax,  as  the  case  may  be,  and  the  cutting  edges  marked  in  several 
places  to  serve  as  guides  in  restoring  the  upper  and  lower  waxes  to  their 
correct  relation  with  each  other  should  they  become  separated.  The 
articulating  models  are  prepared  in  the  usual  way — pouring  plaster 
into  the  lower  plate,  first  allowing  it  to  extend  back  sufficiently  to 
receive  the  upper  half,  which  is  to  be  poured  next.  The  modelling 
compound  or  wax  is  then  to  be  removed  and  the  teeth  arranged  and 
waxed  up  and  vulcanized.  The  attachment  of  the  vulcanite  to  the 
plate  may  be  secured  by  freely  nicking  the  ridge  to  which  the  teeth  are 
to  be  fastened  by  means  of  a  sharp-pointed  graver,  but  without  this 
the  undercut  of  the  rims  and  buttons  will  be  ample  to  hold  the  vulcanite 
securely  to  the  metal. 

Aluminum,  though  not  affected  by  sulphur,  is  not  as  well  suited  for 
vulcanite  attachments  as  the  other  metals  named,  on  account  of  the 
want  of  reliable  aluminum  solder  "^'ith  which  to  fasten  the  loops  or  pins 
thoroughly;  but  by  special  treatment,  which  will  be  described  in 
connection  with  the  manner  of  preparing  aluminum  plates,  a  compar- 
atively durable  denture  can  be  made  of  that  metal  with  vulcanite. 
Recently  casting  methods  have  been  so  improved  as  to  make  the  use 
of  cast  aluminum  with  a  vulcanite  attachment  a  thorouglily  satisfactory 
procedure. 

In  constructing  a  denture  of  gold  with  vulcanite  attachments  the 
plate  should  be  of  the  thickness  of  No.  27  of  the  standard  gauge,  and 


528 


VULCANIZED  RUBBER  AS  A   BASE. 


made  in  accordaiicc  with  the  directions  for  tlie  makiiifr  of  gold  and  silver 
plates  in  Chapter  XI\'. 

It  should  he  provided  with  a  rim  extending  entirely  around  the  labial 
and  buccal  edges  and  upon  the  palatal  portion  of  the  plate  slightly  pos- 
terior to  the  alveolar  ridge,  as  shown  in  A  and  B  in  Fig.  498.  This 
rim  may  be  formed  of  Xo.  27  plate  (Fig.  498)  or  round  wire  of  Xo.  17 
gauge  (Fig.  499).     A  rim  formed  of  round  or  triangular  wire  requires 


Fig.  498 


Cross  section  of  gold  plate  showing  soldered  rim. 

much  less  labor  and  time  in  its  adjustment  and  soldering  than  if  formed 
of  a  strip  of  plate,  and  when  flattened  with  the  file  on  the  labial  side, 
and  the  corundum  wheel  and  graver  on  the  lingual  side,  it  has  the  same 
effect  as  if  it  w'as  formed  of  plate. 

Fig  499 


Wire  rim. 


The  rim  may  be  dispensed  with  entirely,  but,  as  it  gives  a  more  fin- 
ished appearance  to  the  denture  and  adds  greatly  to  its  strength,  it 
should,  therefore,  always  be  preferred. 

In  attaching  a  flat  rim  to  a  gold  or  silver  plate  a  strip  of  plate  long 
enough  to  extend  entirely  around  the  rubber  attachment,  should  be  cut. 


VULCANITE    WITH  PLATES  OF  FUSIBLE  ALLOY. 


529 


The  rim  should  be  annealed,  and  bent  with  the  pliers  to  fit  the  la})ial 
and  buccal  edges  on  the  plate.  It  is  then  placed  on  a  charcoal  support, 
and  the  rim  held  in  contact  with  the  plate  by  means  of  small  nails  or 
tacks :  it  is  then  united  to  the  plate  by  a  small  piece  of  solder  immediately 
in  front  at  the  frfenum  and  at  one  or  two  other  points  along  the  buccal 
edo-es.  The  plate  is  then  cooled,  placed  upon  the  plaster  cast,  and 
with  a  small  hammer  and  pliers  the  rim  is  brought  in  close  enough  con- 
tact with  the  plate  to  admit  of  complete  soldering.     The  lingual  por- 


FiG.  500 


Location  of  wire  attachments. 


tion  of  the  rim  shauld  not  be  soldered  to  the  plate  until  after  the  correct 
position  of  the  teeth  has  been  ascertained.  This  is  accomplished  by 
arranging  the  teeth  according  to  the  bite  and  other  reciuirements  of  the 
case,  and  then  making  a  wall  of  plaster  around  them,  separated  at  the 
centre  line.  This  enables  the  operator  to  mark  upon  the  plate  with  a 
sharp  instrument  the  correct  point  at  which  to  solder  the  rim,  so  that  it 
will  leave  an  unbroken  surface  for  the  tongue,  as  shown  by  B  in  Fig.  498 
and  to  mark  the  proper  position  for  the  loops  or  bent-pin  attachments, 
as  shown  by  C  in  Fig.  500.  It  is  very  important  that  the  exact  location 
of  these  fastenings  should  be  ascertained,  but  this  cannot  be  determined 
until  after  the  teeth  have  been  adjusted.     Any  attempt  to  solder  the 


Fig.  501 


Fig.    502 


Incorrect  location  of  rim. 


Incorrect  location  of  rim  and  attachment. 


rim  or  fastenings  previous  to  the  fitting  and  arrangement  of  the  teeth 
will  be  but  guesswork,  and  nearly  always  result  in  either  of  the  con- 
ditions shown  in  Figs.  501  and  502. 

34 


i30 


VULCAXIZED  RUBBER  AS  A  BASE. 


Fig.    oOS 


The  wire  rim  is  soldered  to  its  place 
by  simply  clamping  the  wire  to  the  plate, 
and  then  attaching  it  at  single  points  in 
front  and  at  the  buccal  edges,  and,  after 
the  correct  position  of  the  teeth  has  been 
ascertained,  bringing  it  entirely  around  at 
the  Ungual  portion,  as  shown  by  Cin  Fig. 
500  By  simple  pressure  with  an  instru- 
ment or  gently  tapping  with  a  riveting 
hammer,  it  may  be  brought  into  close  con- 
tact with  the  plate  and  completely  sol- 
dered. It  need  not  be  flattened  and  fin- 
ished until  after  the  case  is  vulcanized. 

Owing  to  the  difficulty  in  soldering 
aluminum,  it  is  necessary  to  secure  at- 
tachment for  the  vulcanite  to  the  plate  by 
means  of  perforations  or  countersunk 
holes  along  the  top  of  the  ridge.  For 
this  purpose  ingenious  perforating  punch- 
es have  been  devised  by  Drs.  Rich- 
mond,    Peck,     and    others;     those     of 


Fig.  504 


Perforating  forceps  No.    9. 
Fig.  505 


Loop  punch. 


Pei-forated  plate. 


VULCANITE  PLATES   WITH  GOLD-FOIL,   ETC. 


531 


the  two  former  are  shown  by  Figs.  503  and  504,  the  latter  throwing 
up  a  sharp  square  burr,  the  former  a  loop.  The  punch  points  entering 
from  the  under  side  of  the  plate,  produce  the  desired  result  without 
in  the  least  bending  or  affecting  the  fit  of  the  plate. 

A  rolled  aluminum  plate,  constructed  in  the  manner  shown  by  Fig. 
505,  and  roughened  by  means  of  the  punches  (Figs.  503  or  504),  and 
with  the  teeth  attached  by  means  of  vulcanite,  will  afford  a  light,  strong, 
and  comparatively  durable  denture. 

,  Vulcanite  is  of  great  value  in  refitting  gold  plates  which  have  ceased 
to  fit  the  mouth  in  consequence  of  changes  by  absorption  following  the 
extraction  of  the  teeth.  These  changes  may  continue  in  some  cases  for 
several  years  after  the  removal  of  the  natural  organs,  to  such  an  extent 
finally  that  the  denture  will  no  longer  be  of  service.  The  resorption 
usually  occurs  along  the  alveolar  ridge,  and  it  is  a  matter  requiring  but 
little  time  or  labor  to  adjust  the  denture  to  a  new  plaster  cast,  fill  the 
spaces  caused  by  resorption  with  wax,  invest,  pack,  and  vulcanize  the 
piece.  Care  must  be  observed  to  make  countersunk  perforations 
through  the  plate  at  points  where  the  vulcanite  is  to  be  attached,  so  as 
to  secure  firm  union  with  the  gold  plate. 

Vulcanite  Plates  Lined  with  Gold-foil,  Electro-deposits,  etc — Various 
experiments   have   been   made  with  this    class  of    work  in  the  last 


Fig.  506 


The  vulcan  gold  lining. 

twenty-five  years,  with  a  view  to  developing  some  process  by  which 
a  durable  metallic  coating  can  be  given  to  that  portion  of  the  vulcanite 
denture  which  is  in  contact  with  the  alveolar  process  and  maxillary  por- 
tion of  the  mouth.  There  are  two  methods.  One  consists  in  coating 
the  surface  of  the  plaster  cast  vnth  gold  by  electro-deposition,  by  first 
rendering  it  impervious  to  warm  water,  so  that  it  will  not  take  up  and 
destroy  the  gold  bath.  The  surface  to  be  electro-plated  must  be  hard  and 
smooth  and  free  from  all  greasy  substances.     It  must  be  thoroughly 


532  VULCANIZED  RUBBER  AS  A  BASE. 

coated  with  plumbago  and  painted  with  a  solution  of  chloride  of  gold 
to  facilitate  rapid  deposition  over  the  whole  surface. 

The  next  and  simplest  form  is  to  coat  sheets  of  No.  8  or  10  gold-foil 
with  a  non-conductor  on  one  side,  or  by  putting  two  sheets  together 
with  a  non-conductor — as  wax,  for  instance — between  them,  and  seal- 
ing the  edges  with  w'ax  to  prevent  the  gold  solution  from  penetrating 
between  or  through  the  sheets.  A  rough  granular  coating  of  gold  or 
copper  can  be  deposited  on  the  exposed  sides,  which  will  ensure  com- 
paratively good  adhesion  with  the  plate  after  vulcanzing. 

Another  method  is  w^hat  is  known  as  the  "Vulcan  gold  lining."  It 
is  a  pure  gold  sheet  covered  on  one  side  with  a  thin  coating  of  silver 
(Fig.  506.)  The  gold  is  applied  in  one  piece  to  the  surface  to  be  cov- 
ered, and  no  extra  care  is  required  in  packing  the  flask.  The  lining  is 
of  chemically  pure  gold  on  one  side  with  a  thin  covering  of  pure  silver 
on  the  other.  The  union  betw^een  the  rubber  plate  and  the  gold  lining 
is  mechanical :  the  sulphur  in  the  rubber  acting  upon  the  surface  of  the 
silver  produces  a  condition  of  surface  which  favors  adhesion. 

This  foil  is  of  the  thickness  of  No.  40.  In  applying  it,  the  case  should 
be  packed  first;  the  flask  is  then  separated,  and  any  imperfections  in  the 
casts  are  to  be  repaired  wuth  thin  plaster  or  oxyphosphate  cement. 
The  cast  is  then  to  be  painted  with  a  thin  solution  of  equal  parts  of 
shellac  and  sandarac  dissolved  in  alcohol.  When  dry,  coat  the  surface 
with  dextrin,  gum  tragacanth,  or  damar  varnish,  and  while  still  moist 
and  sticky,  press  small  pieces  of  the  gold  lining  on  to  the  cast,  bright 
side  down.  The  gold  lining  is  first  cut  into  convenient  strips  of  the 
form  of  rectangles,  sc|uares,  and  triangles,  to  avoid  wrinkling.  The 
edges  should  slightly  overlap,  and  the  lining  be  kept  free  from  varnish 
or  any  substance  that  would  be  likely  to  interfere  with  adhesion.  Pres- 
sure on  the  granular  side  of  the  foil  with  a  steel  instrument  should  also 
be  avoided.  The  rubber  end  of  a  lead  pencil  or  the  finger  is  the  best 
means  of  pressing  the  gold  into  all  the  irregularities  of  the  cast.  The 
flask  should  then  be  carefully  closed  and  the  piece  vulcanized. 

Dr.  John  A.  Daly,  of  Washington,  D.  C,  has  described  a  method  of 
lining  new  and  old  rubber  plates  as  follows:  "The  vulcanite  denture  is 
constructed  and  finished  in  the  usual  way;  the  surface  to  be  covered 
with  the  gold  lining  is  washed  with  soap  and  water  until  perfectly  clean. 
A  sharp-pointed  instrument — excavator,  knife-blade,  or  needle-point — 
is  then  employed  to  scratch  or  serrate  the  entire  surface  to  be  covered. 
Care  must  be  observed  to  keep  it  clean,  and  the  roughened  part  should 
not  be  touched  with  the  fingers.  A  solution  of  ordinarv  dental  rubber 
in  naptha  is  then  to  be  evenly  painted  over  the  prepared  surface  and 
allowed  to  dry  to  the  point  of  stickiness.  The  lining  of  gold,  which  is 
the  form  of  foil  of  about  No.  60,hasone  side  roughened  by  the  electro- 
deposition  of  gold.  A  strip  of  the  foil  is  cut  of  sufficient  size  with  which 
to  form  the  rim,  which,  when  in  position,  will  enable  the  operator  to 
handle  the  plate  without  soiling  the  rubber  surface  (no  harm  will  re- 
sult from  handling  the  gold).  Where  there  are  depressions,  the  lining 
should  be  pressed  with  a  suitably  shaped  piece  of  rubber  eraser  to  the 


VULCANITE  PLATES  WITH  GOLD-FOIL,  ETC. 


533 


lowest  point  in  the  plate.  It  should  be  cut  in  pieces  of  such  size  as  will 
avoid  wrinkling,  and  applied  so  that  each  piece  will  slightly  overlap  the 
other.  All  creases  are  to  be  removed  by  gentle  pressure  with  an  egg- 
shaped  burnisher.  The  plate  is  then  flashed  in  the  usual  way  and  vul- 
canized for  twenty-five  minutes  at  from  320°  to  330°  F.  It  will  re- 
quire no  finishing  when  removed  from  the  flask,  except  where  the 
edges  of  the  lining  overlap.  The  laps  must  be  removed  carefully  with 
a  blunt  instrument,  such  as  a  dull  knife-blade,  burnisher,  or  the  finger- 
nail, bending  them  back  and  forward  until  they  break. 

If  the  plate  has  been  worn  for  some  length  of  time,  it  should  be 
placed  for  fifteen  minutes  in  a  concentrated  solution  of  lye  or  soda,  and 
thoroughly  cleansed  before  the  surface  is  roughened  and  coated  with 
the  rubber  solution. 

The  gold  lining  of  Dr.  Daly  may  be  applied  during  the  construction 
of  a  new  denture  by  first  varnishing  the  plaster  cast,  after  flashing, 
with  sandarac  varnish,  followed  by  a  coating  of  damar  varnish;  and 
while  the  latter  is  sticky  the  cast  is  covered  with  the  gold  lining  cut 
in  pieces  of  about  half  an  inch  in  width.  The  brown  side  of  the  gold, 
which  is  the  roughened  surface,  must  be  up,  so  as  to  engage  the 
rubber  in  packing,  the  rest  of  the  operation  being  in  every  respect 
similar  to  the  ordinary  procedure  of  filling  and  closing  the  flask. 


Fig.  507 


Surface-cohesion  forms  for  artificial  dentures. 


The  smooth  side  of  the  gold  lining  is  like  ordinary  gold  foil,  and  is  the 
surface  intended  to  be  in  contact  with  the  mucous  membrane.  The 
roughened  surface,  which  has  a  brownish  color,  is  prepared  so  as  to  in- 
sure strong  adhesion  with  the  rubber,  and  the  union  is  said  to  be  so  firm 
that  it  cannot  be  stripped  from  the  vulcanized  plate.  The  gold  lining, 
extra  thin  rubbers,  and  all  other  materials  used  in  this  process  can  be 
obtained  from  dental  depots. 

Dr.  Joseph  Speyer  has  introduced  a  method  of  lining  vulcanite 
and  celluloid  dentures  consisting  of  a  thin  metallic  plate  of  the  thickness 
of  No.  120  foil,  the  surface  of  which  is  covered  with  minute  papilliform 
prominences  (Fig.  507),  which  are  claimed  to  effect  very  strong  surface 


534 


VULCANIZED  RUBBER  AS  A  BASE. 


adhesion,  while  they  cause  no  irritation  and  leave  no  marked  inden- 
tations on  the  tissues.  Fig.  508  shows  the  prominences  magnified  four 
diameters. 

New  Rubber  Facings — Two  comparatively  new  kinds  of  rubber 
have  been  introduced  within  a  few  years  that  commend  themselves 
for  use  in  the  combination  plate  described  above.  One  is  the  "gran- 
ular-gum" rubber  facing  by  Dr.  Gilbert  Walker,  in  the  use  of  which 
the  following  directions  are  given:  "In  waxing  up  a  case,  carefully 
model  the  gum  portions  to  the  exact  contour  desired,  and  make  the 
festoons  smooth  at  the  necks  of  the  teeth.  After  flasking,  face  with  a 
layer  of  granular  gum  cut  to  lie  close  around  the  labial  and  buccal  necks 
of  the  teeth,  and  pack  against  the  outer  wall  of  the  plaster  investment, 
so  that  the  facing  shall  not  extend  above  the  edges  of  the  plaster.  I^ap 
the  pieces  of  granular  gum  carefully,  so  that  the  red  rubber  will  not  be 
squeezed  between  them,  and  show  on  the  facing  after  vulcanizing.     In 


Fig.  509 


Granular-gum  faced  \ulcanite  denturos. 

packing  the  red  rubber  care  must  be  taken  not  to  have  an  excess,  else 
the  overflow  may  carry  with  it  the  granular  gum  and  elongate  its  colored 
particles,  thus  interfering  with  the  mosaic  appearance  on  which  the 
imitation  of  the  gum  depends. 

The  lingual  part  of  the  plate  may  hkewise  be  faced,  with  care  in  lap- 
ping the  pieces  of  granular  gum  and  avoiding  an  overplus  of  red  rubber. 
With  this  form  of  rubber,  exposure  to  sunlight  for  the  purpose  of  devel- 
oping its  color  is  unnecessary;  when  well  polished  the  moisture  of  the 
mouth  will  improve  the  tint. 

Granular  gum  vulcanizes  with  any  of  the  ordinary  rubbers;  better 
results  are,  however,  obtained  by  vulcanizing  it  at  a  low  temperature. 
In  finishing,  care  should  be  exercised  to  avoid  cutting  through  the  thin 
facing." 

Gear's  shaded  pink  rubber  is  somewhat  similar  to  the  granular  gum 
described  above.  It  may  be  used  in  the  same  manner  as  the  latter,  and 
adds  greatly  to  the  beauty  and  natural  appearance  of  the  gum  portion 
of  the  denture  if  the  preliminary  modelling  has  been  done  with  taste  and 
skill. 

Beaded  or  Grooved  Vulcanite  Dentures — For  the  more  complete  ex- 
clusion of  air  and  moisture  between  the  artificial  denture  and  the  mucous 


WEIGHTED  rULCAXITE  DENTURES. 


535 


membrane  upon  which  it  rests,  a  groove  is  cut  in  the  plaster  cast  as 
shown  in  Fig.  510/  so  that  the  vulcanized  denture  should  have  an  in- 
tegral half-round  smooth  bead  formed  on  its  maxillary  surface.  The 
groove  must  be  carried  continuously  across  the  palatal  portion  of  the 
plaster  cast  and  along  the  buccal  and  labial  lines  of  muscle  attach- 
ments, to  form  a  bead-enclosure  which  should  produce  a  supplemental 
chamber-like  function  of  the  entire  inner  surface  of  the  denture.  (Fig. 
510.) 

The  groove  may  be  conveniently  scraped  on  the  plaster  cast  by  one 
of  the  larger-sized  Palmer's  excavators,  which,  being  rounded  at  its  cut- 
ting edge,  will  afford  a  half-round  bead  in  the  vulcanized  piece. 

Fig.  510 


Grooved  plaster  cast. 

Weighted  Vulcanite  Dentures  and  Dentures  with  Contours — As  a 
rule,  lower  dentures  formed  of  vulcanite  have  not  sufficient  weight  to 
overcome  the  resistance  of  the  muscles  of  the  cheeks  and  the  sublingual 
integuments,  and  when  the  bite  is  unusually  short  they  are  also  deficient 
in  strength,  so  that  breakage  of  lower  dentures  is  a  common  occurrence. 
Both  of  these  defects  may  be  remedied  by  constructing  a  platinum  or 
gold  plate  of  two  thicknesses  of  No.  29,  soldering  suitable  anchorages 
near  the  top  of  the  ridge  in  a  position  which  will  not  interfere  with  the 
teeth,  and  vulcanize  as  described  under  the  heading  of  Combination 
Dentures. 

A  less  expensive  method  of  adding  weight  to  a  vulcanite  denture  con- 
sists in  using  rubber,  which  is  prepared  for  the  purpose  with  tin  filings 
incorporated  with  it.  By  this  means  the  requirements  as  to  weight  are 
very  nearly  fulfilled,  but  no  additional  strength  is  acquired,  the  only 
means  of  overcoming  that  difficulty  being  the  use  of  a  metallic  plate. 

^^^len  the  bite  is  unusually  long  it  may  be  waxed  and  flasked  in  the 
usual  manner  and  after  the  flask  has  been  separated  preparatory  to 
packing,  a  cylindrical  rod  of  wax  may  be  laid  upon  the  under  side 

*■  Dental  Cosbios  of  July,  1895,  p.  55. 


536  VULCANIZED  RUBBER  AS  A  BASE. 

of  the  blocks  or  single  teeth,  as  the  case  may  be,  of  sufficient  length  to 
extend  from  one  second  molar  to  the  other.  The  wax  rod  is  then 
carefully  lifted  from  its  place  and  invested  in  plaster  to  forma  mold 
which  should  be  in  two  equal  halves,  the  line  of  division  being  exactly  in 
the  centre  of  the  diameter  of  the  wax  rod.  This  mold  should  have  a 
gate  bored  through  the  top  for  convenience  in  pouring  the  melted  tin, 
while  at  tiie  other  extremity  it  should  be  provided  w^ith  a  vent  to  allow 
the  escape  of  air  at  the  instant  of  pouring  the  melted  tin.  The  tin 
may  be  melted  in  a  small  iron  ladle  with  a  suitable  handle,  and  the 
melting  may  easily  be  accomplished  over  a  gas-jet  or  alcohol  "flame. 
When  the  casting  is  complete  and  the  tin  sufficiently  cool,  the 
mold  may  be  opened  and  the  tin  facsimile  of  the  wax  rod  placed 
in  position  in  the  flask,  resting  upon  the  teeth,  as  previously  indi- 
cated in  the  description  of  the  preparation  of  the  wax  pat- 
tern rod.  The  tin  rod  should  be  so  arranged  that  all  parts  of  it 
will  be  covered  by  the  vulcanite.  Fig.  511  shows  the  arrangement  as  de- 
scribed, A  indicating  the  tin,  B  the  vulcanite.  This  method  possesses 
the  additional  advantage  of  preventing  porosity  of  the  vulcanite — an 
accitlent  which  is  very  liable  to  occur  in  bulky  lower  dentures. 

Fig,  511 


Molded  tin  weighted  vulcanite. 


It  is  sometimes  necessary  to  amplify  the  denture  at  points  where  un- 
natural depression  occurs  in  consequence  of  great  resorption  following 
the  loss  of  canines  or  molars.  If  the  amount  of  projection  required  to 
restore  natural  expression  is  not  extraordinary,  slight  additions  to  the 
rim  and  the  usual  vulcanizing  may  be  relied  upon  to  accomplish  the  de- 
sired result;  but  if  the  case  require  a  large  mass,  exceeding  a  quarter 
of  an  inch  in  thickness,  the  vulcanizing  must  be  done  at  a  lower  tem- 
perature, of,  say,  300°  F.,  and  three  hours'  exposure  in  the  vulcanizer, 
in  order  to  avoid  porosity.  Equally  good  results  may  also  be  attained 
by  forming  a  core  of  some  light  material,  enveloping  it  in  rubber,  and 
filling  with  it  the  recess  in  the  flask  representing  the  "contour."  For 
this  purpose  cores  of  thin  metal  hermetically  sealed,  approximating  the 
form  of  the  contour  and  one-eighth  of  an  inch  smaller  than  the  latter 
may  be  used.  The  preparation  of  metallic  forms  is,  however,  a  matter 
requiring  considerable  labor  and  time.  A  much  simpler  and  equally 
effective  method  is  to  form  a  core  either  of  vulcanized  rubber,  sponge, 
or  cotton  wool  tightly  rolled  and  wrapped  with  thread.  In  packing  the 


VULCANITE  DENTURES  WITH  CONTOURS. 


537 


core  is  not  to  be  placed  in  position  until  the  case  has  been  packed  and 
the  flask  completely  brought  together,  when  it  may  be  opened,  the 
recesses  representing  the  contours  freed  from  rubber,  and  the  cores,  pre- 
viously wrapped  with  strips  of  soft  rubber  to  the  thickness  of  an  eighth 
of  an  inch,  put  in  its  place.  The  object  of  first  packing  and  closing  the 
flask  is  to  prevent  the  flow  of  rubber  from  displacing  the  cores  and  to 


Fig.   512 


Cast  of  mouth  with  opening  into  nasal  cavity. 


ensure  their  complete  envelopment.  In  finishing  such  a  case,  care 
must  be  exercised  to  avoid  cutting  through  the  rubber  or  exposing  the 
sponge  or  cotton  when  those  materials  are  used.  Probably  of  the 
materials  named  a  piece  of  hard  vulcanite  affords  the  best  results  and 
is  less  likely  to  lead  to  failure  through  displacement,  which  is  always 
liable  to  occur. 

Fig.  513 


Denture  constructed  for  case  shown  in  Fig 


The  same  course  as  outlined  above  in  the  preparation  of  ordinary 
contours  may  be  pursued  in  making  plates  to  restore  contours  when 
large  portions  of  the  maxillary  bones  have  been  lost  by  disease  or 
accident,  such  as  gunshot  wounds,  etc.  Fig.  512  shows  a  cast  of  the 
mouth  in  which  the  whole  anterior  portion  of  the  alveolar  ridge  had 
been  removed,  leaving  a  large  opening  into  the  nasal  cavity,  by  which 
speech  was  seriously  affected.      After  obtaining  the  cast  a  thin  plate 


538  VULCANIZED  RUBBER  AS  A  BASE. 

of  wax  was  pre])are(l  to  cover  tht-  j)alatal  j)ortion  extenciing  around  the 
teeth  in  the  form  of  half  clasps,  and  through  the  opening  even  with  the 
floor  of  the  nasal  cavity.  Upon  the  wax  plate  thus  prepared  the  arti- 
ficial teeth  were  arranged,  and  the  waxing  and  flasking  done  in  the 
usual  way.  To  prevent  porosity  of  that  part  of  the  vulcaiu'te  ap])liance 
wiiich  extended  into  the  opening,  two  or  tliree  drops  of  water 
were  introduced,  so  as  to  keep  the  bulb  hollow  and  in  a  state  of  expan- 
sion during  the  vulcanizing  process.  This  water  may  be  removed  after 
vulcanizing  by  drilling  into  the  bulb  and  then  securely  plugging  the 
holes  thus  made  with  platinum  wire  tightly  screwed  in.  Fig  513 
affords  a  sectional  view  of  the  appliance. 

Spiral  Springs. — A'ulcanite  dentures  are  occasionally  retained  in  situ 
by  means  of  spiral  springs.  This  method  of  retention,  is,  however, 
but  seldom  resorted  to,  except  in  cases  of  extreme  flatness  of  the  mouth 
or  else  in  the  correction  of  oral  deformities.  (For  a  description  of  the 
preparation  and  adjustment  of  spiral  springs  the  reader  is  referred  to 
Chapter  XIV.) 

Vulcanite  Plates  and  Flexible  Rubber  Rims. — The  use  of  flexible 
rubbers  in  connection  with  artificial  dentures  is  of  doubtful  value,  on 
account  of  the  inevitable  loss  of  flexibility  of  all  semi-vulcanizable  rub- 
bers when  worn  in  the  mouth. 

REPAIRING  VULCANITE  PLATES. 

The  breaking  of  vulcanite  dentures  is  usually  due  to  over-vulcanizing, 
by  which  elasticity  and  toughness  are  destroyed;  to  improper  arrange- 
ment of  the  molars,  by  which  the  strain  of  mastication  is  thrown  on 
the  outside  instead  of  on  top  of  the  ridge;  or  to  a  warped  plate.  The 
firstevidenceof  the  giving  away  of  apiece  is  usually  a  fine  crack  appear- 
ing between  the  two  central  incisors,  and  sometimes,  in  partial  dentures, 
in  the  border  surrounding  a  natural  tooth. 

Wax  Method  —A  method  particularly  applicable  to  plates  which 
are  broken  entirely  in  two,  consists  in  adjusting  the  two  parts  of  the 
plate  together,  and  fastening  them  in  correct  relation  to  each  other 
temporarily  by  adhesive  wax  dropped  on  the  lingual  surface  until  plas- 
ter can  be  run  into  the  maxillary  portion  of  the  denture.  As  soon  as 
the  plaster  hardens,  the  plate  is  removed  from  the  cast,  the  line  of  divis- 
ion is  enlarged  with  a  file,  and  dovetails  cut  opposite  each  other  with 
a  jeweler's  saw,  as  shown  by  Fig.  514.  The  dovetailed  space  is  then 
filled  with  wax,  invested  in  the  usual  way  in  a  flask,  packed,  and  vul- 
canized. This  method  is  open  to  one  serious  objection; — it  necessi- 
tates another  vulcanizing  and  the  consequent  loss  of  elasticity  and 
toughness.  A  plate  so  treated  will  never  be  as  strong  as  it  was  before. 
By  another  method  the  edges  may  be  adjusted  as  before  described, 
and  the  piece  be  placed  immediately  in  the  lower  half  of  the  flask.  After 
the  plaster  has  set,  the  adhesive  wax  is  to  be  removed  from  the  lingual 
side  of  the  plate  and  a  line  cut  with  a  round  engine  bur  along  the 


REPAIRING  VULCANITE  PLATES. 


539 


full  extent  of  the  crack,  or  break,  halfway  through  the  plate  and  a 
quarter  of  an  inch  wide,  with  smooth,  regular  edges,  without  dovetails. 
The  case  is  then  waxed  up  and  the  other  half  of  the  flask  poured — 


Fig.    514 


Fractured  vulcanite  plate  dovetailed  for  repair. 


when  the  case  is  packed  and  vulcanized.     If  the  parts  have  been  kept 
perfectly  clean  the  union  will  be  quite  strong. 

Another  modification  \  which  gives  the  best  results  is  this.     After 


Fig.  515 

l~ 

M^l^HiM 

^M 

^Kr 

m}  ^^ 

B^l 

^^^M 

i^H 

P^i 

^i 

^^^^  ^^jfilll 

pi 

^H^|l,^Fm%'" 

•T 

•     WSg-'.' 

lo 

■n 

mm 

^ ''-'U^bJH^^^^B 

Fractured  vulcanite  plate  prepared  for  repairing  with  beveletl  surface  and  wax  shafts. 


the  cast  is  made,  the  portions  of  the  plate  are  removed  from  the  cast 
and  with  file  and  scraper  a  long  bevel  is  cut,  forming  a  thin  feathery 
edge  along  the   fractured  edge  and  sloping   away  from  this  for  an 


^  The  method  preferred  by  the  writer. 


540 


VULCANITE  RUBBER  AS  A   BASE. 


eighth  to  one-half  inch  as  the  case  will  permit.  (V'l^.  515.)  The  pieces 
are  then  filed  to  give  a  slight  bevel  upon  the  maxillary  surface.  The 
portions  of  the  plate  which  have  been  cut  away  are  replaced  with 
wax,  and  if  necessary  the  plate  may  be  thickened  over  the  portion  hav- 
ing the  freshly  cut  surface.  It  is  unnecessary  to  coat  the  vulcanite  sur- 
face with  a  solution  of  rubber  as  the  heat  and  i)ressure  will  make  the 
union.  Fig.  510  shows  method  of  Hasking.  For  description  of  wax 
shafts,  see  page  499. 


Fig.  516 


Fractured  vulcanite  plate  shown  in 


vested. 


Fusible  Metal  Method. — To  avoid  loss  of  strength  by  the  second  vul- 
canizing it  is  recommended  that  fusible  metal,  melting  at  150°  or] 60° 
F.,  be  used  to  fill  the  dovetailed  space.  This  can  be  .done  by  pouring 
the  melted  alloy  into  the  space  and  packing  it  w'ith  a  hot  spatula, 
which  is  readily  admissible  owing  to  the  low  fusing-point  of  the  metal. 
AVhile  the  method  has  the  advantage  of  not  requiring  a  second  vulcan- 
izing, the  union  of  the  metal  at  the  point  of  fracture  is  not  as  close  as 
when  rubber  is  used,  and  it  cannot  be  said  to  be  reliable  as  a  means 
of  repairing  broken  vulcanite  plates. 

A  single  tooth  may  be  fastened  to  the  vulcanite  by  filing  the  dove- 
tailed space  as  for  repairing  with  rubber,  the  fusible  metal  to  be  put 
in  place  with  a  hot  spatula;  or  the  dovetail  can  be  filled  with  amalgam. 

Replacing  Vulcanite  Method. — ]Much  the  better  way  is  to  fasten  the 
parts  together,  run  a  ])laster  cast  into  the  denture,  then  make  a  bite  of 
plaster  to  serve  as  a  guide  for  the  replacement  of  the  teeth,  remove  the 
latter  from  the  broken  plate,  reset  them  to  the  cast,  w'ax  up  the  piece, 
flask,  and  vulcanize.  This  affords  practically  a  new  case,  and  the  time 
consumed  is  not  much  greater  than  is  required  in  repairing  the  old  one. 


INTERDENTAL  SPLINTS.  541 

Additions  to  Old  Plates. — Additions  of  teeth  to  old  plates  are  accom- 
plished after  practically  the  same  methods.  Fig.  517  shows  a  case  where 
six  teeth  have  been  extracted,  and  the  old  plate  is  prepared  for  the  ad- 
tlition  of  as  many  porcelain  teeth,  so  that  the  denture  could  be  worn 
until  the  resorption  of  the  alveoli  and  gums  would  admit  of  the  con- 
struction of  a  permanent  plate.  The  illustration  shows  the  plate  bev- 
elled oflf  to  a  smooth  edge,  and  several  holes  drilled  into  the  filed  portion. 
The  correct  occlusion  of  the  new  teeth  is  obtained  by  placing  the  plate 

Fig.  517 


Plate  prepared  for  the  addition  of  several  teeth. 

in  the  mouth  after  the  bleeding  ceases,  placing  two  pieces  of  softened 
wax  along  the  alveolar  ridge  and  plate,  and  directing  the  patient  to 
bite  into  the  wax,  and  then  gently  pressing  the  wax  while  the  teeth 
are  in  contact.  This  gives  the  correct  relation  of  the  lower  to  the  upper 
teeth,  and  the  impression  of  that  portion  of  the  alveolar  ridge  to  be 
covered  by  the  addition  to  the  plate.  The  preparation  of  the  plaster 
cast  and  bite  is  done  in  the  usual  way,  plain  teeth  being  ground  to  the 
gums  to  allow  for  the  rapid  resorption  which  always  follows  the  extrac- 
tion of  teeth.     The  waxing  and  flashing  are  done  in  the  usual  wav. 

Ironing-in  Method. — This  method  is  suitable  for  replacing  a  tooth 
or  two,  or  filling  a  short  crack  or  a  hole.  The  vulcanite  is  cut  with  a  file 
to  give  a  dovetailed  form  to  the  space  into  which  a  tooth  is  to  be 
added;  and  a  crack  or  hole  should  be  prepared  for  the  new  rubber 
with  a  scraper.  The  new  rubber  is  ironed  into  place  by  using  a  hot 
wax  spatula  and  firm  pressure.  Waxable  rubber  is  better  for  this 
work  than  ordinarv  rubber. 


INTERDENTAL    SPLINTS. 

Interdental  sphnts  in  conjunction  with  submental  compresses  and 
occipito-mental  bandages  have  been  used  by  surgeons  in  the  treatment 
of  fractured  jaws  since  1780. 

Drs.  F.  B.  Gunning  of  New  York  and  J.  B.  Bean  of  Atlanta,  Georgia, 


542 


VULCANIZED  RUBBER  AS  A   BASE. 


were  the  first  to  describe  methods  of  constructiii<i;  interdental  splints  of 
vulcanized  ruhl)er.  Both  of  these  gentlemen  claimed  priority,  and  it 
appears  that  the  invention  was  made  and  published  independently  by 
each  at  about  the  same  period. 

The  interdental  splints  of  Drs.  Gunning  and  Bean  were  similar,  ex- 
cept that  the  arrangement  of  the  submental  compress  and  bandage  of 
Dr.  Bean  differed  materially  from  that  used  by  Dr.  Gunning. 


Fig.    51  S 


Gunning  interdental  splint. 


Mental  compress. 


The  Gunning  splint  (Fig.  518)  covered  both  the  upper  and  lower 
teeth,  and  was  provided  with  an  opening  in  front  for  the  reception  of 
food,  a  bandage  over  the  head  being  used  as  a  means  of  securing  ad- 
justment of  the  lower  jaw  ^dth  the  splint.  Other  splints  were  used  by 
Dr.  Gunning  which  co\'ered  the  low^er  teeth  only,  leaving  the  motions 
of  the  jaw  free.  Fig.  519  shows  the  arrangement  of  the  mental  com- 
press and  bandages  employed  by  Dr.  Bean  to  maintain  the  relation  of 
the  jaws. 

The  preliminary  steps  in  the  treatment  of  fractures  of  the  jaw  are 
generally  made  more  or  less  difficult  by  the  pain  and  swelling  incident 
to  the  injury.  For  the  impression,  plaster-of-Paris  is  by  far  the  most 
suitable  material,  as  it  necessitates  less  bulk  and  may  be  applied  with 
much  less  force  than  is  required  to  press  wax  or  modelling  compound  to 
complete  contact  with  the  teeth.  If  plaster-of-Paris  be  intelligently  and 
skilfully  employed  in  these  cases,  no  violence  need  be  used  either  in  its 
application  or  removal.  An  impression  tray  of  the  proper  size,  with  a 
smooth  and  polished  surface,  should  be  selected  and  oiled  to  ensure  its 
easy  separation  from  the  plaster  when  hard.  The  latter  should  be  of 
the  finely-ground  variety,  such  as  is  furnished  by  the  dental  depots  for 
impression  purposes,  and  which  hardens  quickly,  breaks  with  a  sharp 
fracture,  and  requires  but  little  force  in  its  removal. 


INTERDENTA  L  SrL  I  NTS. 


543 


The  tray,  filled  suflficiently  with  plaster,  is  applied  while  the  latter  is 
still  quite  soft  and  held  until  it  sets.  The  tray  is  then  separated  from 
the  plaster  with  scarcely  any  force;  the  plaster  impression  is  gently  re- 
moved in  pieces  from  around  the  teeth,  and  the  pieces  placed  in  their 
proper  re  ation  to  each  other  in  the  tray.  If  any  of  the  teeth  have  been 
loosened  by  the  injury  to  the  jaw,  the  use  of  plaster  of  Paris  is  especially 


Fig.  520 


Casts  of  fractured  jaw. 


indicated    in   order    to    avoid   their   displacement  by   the  downward 
pressure  of  wax  or  modelling  compound. 

If  the  fracture  be  of  a  complicated  nature  and  accompanied  with  con- 
siderable displacement  of  the  parts,  as  shown  in  Fig,  520,  no  persistent 
effort  need  be  made  to  restore  the  deranged  fragments,  as  that  part 
of  the  operation  can  be  just  as  well  accomplished  on  the  plaster  cast,  the 

Fig.    521 


The  casts  cut  and  the  plaster  teeth  placed  in  their  natural  position. 


patient  being  thus  relieved  from  the  additional  suffering  which  would  be 
sure  to  attend  any  attempt  to  set  the  broken  parts  of  the  jaw. 

An  impression  is  then  taken  of  the  upper  teeth,  the  positions  of  which 
even  when  the  superior  maxilla  is  broken,  are  not  likely  to  be  changed. 
When  the  casts  have  been  obtained  cuts  may  be  made  with  a  fine  saw 
through  the  cast  of  the  lower  jaw  at  points  corresponding  with  the  frac- 


544 


VULCANIZED  RUBBER  AS  A  BASE. 


tures,  and  the  articulation  corrected  by  adjustment  to  the  upper  teeth 
(Fiji:.  521),  which  will  serve  the  ojjcrator  as  infallible  ji;uides.  The  parts 
of  the  lower  cast  are  then  secured  in  their  corrected  relation  by  addi- 
tional plaster:  no  effort  need  be  made  to  set  the  jaw  after  the  impres- 
sion is  taken  until  the  splint  is  ready  for  adjustment. 

To  preserve  the  proper  relation  of  the  lower  to  the  upper  teeth,  the 
cast  should  be  placed  in  an  articulator.     (Fig.  522.) 

Fig.  522 


Corrected  casts  upou  the  articulator. 

The  set  .screw  of  the  articulator  should  be  arranored  so  as  to  allow  for 
a  separation  between  the  upper  and  lower  teeth  of  about  a  quarter  of  an 
inch.  While  it  is  desirable  that  the  splint  when  finished  should  fit  the 
teeth  and  ^ums  with  sufficient  closeness  to  enable  it  to  serve  the  purpo.se 
for  which  it  is  designed,  it  must  be  borne  in  mind  that  to  save  the  patient 
from  additional  pain  in  its  adju.stment,  it  is  necessary  that  the  fixture 
.should  go  immediately  to  its  place,  without  delay  or  repeated  trials. 
To  accomplish  this,  the  pla.ster  teeth  and  gums  for  about  a  quarter  of 
an  inch  above  the  necks  should  be  carefully  covered  with  No.  60  tin- 
foil, for  the  purpose  of  slightly  enlarging  the  splint  and  to  secure  a 
smooth  surface  to  the  inside  of  it.  Interdental  dovetailed  space  may 
be  arranged  by  filling  the  undercuts  with  plaster  before  applying  the 
foil,  or  by  trimming  away  retaining  points  in  the  finished  piece  with  a 
sharp  knife-blade  or  engine  bur,  so  that  the  splint  may  be  applied  or  re- 
moved without  much  force.  The  splints  are  then  formed  on  the  plaster 


INTERDENTAL  SPLINT. 


545 


casts  of  thin  sheet  wax  of  a  uniform  thickness  slightly  in  excess  of  a 
sixteenth  of  an  inch;  wax  of  a  sufficient  thickness  is  then  placed  be- 
tween for  the  i)urp()se  of  uniting-  them,  as  shown  by  Fig.  523. 

The  upper  and  lower  splints  are  to  be  carefully  united  and  made 
perfectly  smooth  by  means  of  a  hot  spatula. 


Fig.  523 


Wax  model  for  interdental  splint. 

The  wax  splint  is  next  to  be  removed  from  the  cast  and  invested  in  a 
suitable  flask  in  the  usual  way.  The  casts  may  be  removed  from  the 
articulator  for  the  purpose  of  vulcanizing  upon  them;  this,  however,  is 
not  really  necessary.  It  is,  indeed,  a  better  plan  to  preserve  the  casts 
and  articulation  to  assist  in  the  preparation  of  the  finished  splint  for 
final  adjustment.  A  much  better  way  is  to  carefully  fill  the  deep  parts 


Fig.   524 


Cross  section  of  the  flasked  wax  model. 


of  the  wax  splint  with  plaster  by  means  of  a  camel's-hair  brush,  and 
then  invest  with  the  line  of  division  at  about  the  middle,  as  shown  by 
the  dotted  line  in  Fig.  524. 

The  tin-foil  should  extend  about  an  eighth  of  an  inch  beyond  the 
wax;  it  will  thus  be  held  securely  by  the  investment,  and  disarrange- 

35 


546 


VULCANIZED  RUBBER  AS  A  BASE. 


ment  when  the  flask  is  separated  for  the  removal  of  the  wax  will  be 
avoided. 

A  sectional  view  of  the  flask  with  the  encased  splint  is  given  in  Fig. 
524.  The  flask  is  shown  by  F;  the  casts  by  M;  the  plaster  en- 
casement by  P;  tin-foil  covering  the  teeth  with  extension  beyond  the 
waxsphntby  T;  the  wax  pattern  of  splint  in  the  centre. 

Thv.  same  precautions  recommended  for  the  waxing,  flashing,  and 
packing  of  ordinary  vulcanite  dentures  should  be  observed  in  the  con- 
struction of  spliwts,  but  especial  care  should  be  observed  in  the  separa- 
tion of  the  flask  to  avoid  breaking  the  thin  plaster  teeth,  as  such  an 
accident  would  greatly  embarrass  the  subsecjuent  steps  of  the  operation. 


Fig.  525 


Kingsley's  splint. 

The  flask  should,  therefore,  previous  to  any  attempt  to  separate  it,  be 
placed  in  hot  water,  and  allowed  to  remain  until  the  wax  is  quite  soft. 
After  the  separation  the  last  particle  of  wax  should  be  washed  away  by 
means  of  a  stream  of  boiling  water. 

The  packing  of  the  rubber  demands  more  than  ordinary  care  to  en- 
sure its  being  carried  into  the  deep  and  narrow  spaces  around  the  teeth. 
The  rubber  should  be  cut  into  thin  strips,  softened  over  boiling  water, 
and  carried  into  the  matrix  by  a  suitable  instrument,  such  as  an  old 
plugger.  There  should  of  course,  be  a  slight  excess  of  rubber.  The 
vents  may  be  as  for  ordinary  dentures. 

Interdental  splints  need  not  be  thicker  than  is  consistent  with  suflS- 
cient  strength.  They  should  be  well  finished,  and  provided,  when 
achnissible,  with  a  front  opening,  as  shown  in  Fig.  523,  large  enough 
for  the  passage  of  a  feeding-tube. 

An  interdental  splint  cannot  usually  be  relied  upon  to  immovably 
retain  the  broken  jaw  without  the  assistance  of  bandages,  screws,  wires, 


INTERDENTAL  SPLINTS. 


547 


or  ligatures.  Fig.  525  (Kingsley's  Oral  Deformities)  shows  the  use  of 
screws  passed  through  the  spHnt  at  points  between  the  cervical  por- 
tions of  the  crowns  of  the  molar  teeth. 

Fig.  526  {ibid.)  illustrates  a  splint  provided  with  arms  of  steel  wire 
one-eighth  of  an  inch  in  diameter,  arranged  to  come  "  out  of  the  mouth 


Fig.  526 


A  dent  al  splint  for  the  mandible  in  position. 
Fig.  527 


Mode]  of  mandibular  splint  on  the  articulator. 


when  the  splint  is  in  position,  passing  back  along  the  cheek  on  a  line 
with  the  teeth."  This  splint  was  invented  by  Dr.  Norman  W.  Kings- 
ley,  and  the  description  of  it,  with  the  illustration,  is  from  his  valuable 


548  VULCANIZED  RUBBER  AS  A   BASE. 

work  on  Oral  Deformities.     Fifj.  526  shows  the  sphnt  in  position  and 
the  submental  compress  attached  to  the  side-bars. 

It  will  be  seen  that  this  s})lint  covers  the  lower  teeth  only,  and  that 
its  top  occludes  with  the  upper  teeth  to  admit  of  mastication.  The  con- 
struction of  such  a  splint  is  accomplished  by  placino;  upper  and  lower 
casts  in  an  articulator,  forming  the  wax  splint  as  before  described,  ar- 
ranging the  occlusion  so  that  contact  of  the  upper  teeth  will  be  uniform, 
imbedding  two  stout  steel  wires  with  flattened  lends  in  the  w^ax,  so  that 
they  will  bear  the  strain  which  will  be  required  of  them  while  the  splint 
is  in  position.  Fig.  527  shows  the  waxed  splint  with  side-bars  in  the 
articulator  ready  for  investment.  The  particular  flask  best  adapted 
for  the  vulcanizing  of  interdental  splints  is  oblong  in  form,  and  is  larger 
than  ordinary  vulcanite  flasks;  it  is  known  as  the  "box  flask." 


CHAPTER    XIV. 

SWAGED  METALLIC  PLATES. 
By  William  H.  Trueman,  D.  D.  S. 

The  sheet  metals  employed  as  bases  of  support  for  artificial  teeth  are 
gold,  silver,  platinum,  and  aluminum. 

Platinum  is  rarely  used  as  a  base-plate  for  soldered  dentures;  it  is 
too  soft;  its  relative  infusibilty,  however,  fits  it  for  employment  when 
covered  by  substances  fusing  at  a  high  temperature,  as  when  faced  with 
porcelain  in  continuous-gum  dentures.  An  alloy  of  platinum  and  iri- 
dium, known  as  iridio-platinum,  is  occasionally  employed  in  making 
plates,  the  addition  of  iridium  producing  a  very  rigid  alloy.  It  is 
difficult  to  work,  and  more  expensive  than  gold.  It  is  said  to  with- 
stand the  oral  secretions  better  than  gold  alloys.  The  slight  advantage 
it  may  have  in  this  respect  is  over-balanced  by  its  objectionable  color 
and  excessive  weight. 

Aluminum  is  occasionally  employed  as  a  base-plate,  the  denture 
proper  being  mounted  in  vulcanite.  Its  lightness  and  comparatively 
easy  working  properties  recommend  it;  the  impracticability  of  neatly 
and  effectively  soldering  it  very  much  impairs  its  usefulness  in  dental 
prosthesis. 

Sheet  gold  for  making  plates  is  usually  eighteen  carats  fine,  that  is, 
each  pennyweight  contains  eighteen  grains  of  pure  gold  and  six  of  alloy. 
This  has  long  been  accepted  as  a  standard.  It  is  sufficiently  fine  to 
withstand  the  corroding  tendencies  of  the  oral  fluids,  and  sufficiently 
rigid  for  strength,  if  the  alloy  contains  a  portion  of  either  copper 
or  platinum.  Gold,  silver,  and  platinum,  when  pure,  are  very  soft  and 
pliable,  and  alloys  of  gold  and  silver,  or  gold  and  platinum,  in  which 
the  gold  greatly  predominates  differ  but  little  in  this  respect  from  the 
pure  metals.  Pure  copper  is  a  little  less  soft,  yet  a  small  portion  con- 
fers upon  the  alloy  a  remarkable  rigidity.  An  alloy  of  gold  twenty-one 
parts  to  three  parts  of  platinum,  while  showing  the  presence  of  platinum 
by  a  marked  change  in  color,  is  almost  as  soft  and  pliable  as  either  of 
its  components;  the  addition  of  a  small  portion  of  copper,  or  of  copper 
and  silver,  makes  an  alloy  as  elastic  and  rigid  as  tempered  steel;  it  is  in- 
deed, the  alloy  known  in  dental  prosthesis  as  platinous  or  clasp  gold, 
used  on  acount  of  its  strength  and  elasticity  to  re-enforce  weak  areas 
in  plates  made  of  more  pliable  alloys,  and  for  clasps  and  springs. 

It  is  advisable,  and  will  save  much  trouble  in  utilizing  gold  scraps 
and  filings,  to  limit  the  varieties  of  gold  plate  and  solder  used  in 
dental  plate  work,  and  to  select  and  use  exclusively  a  few  stand- 
ard formulas  judiciously  chosen.  For  plates,  eighteen  carat  is 
commonly  used;   a  lower  grade  than  eighteen  is  inadmissible,  and 

549 


550  SWAGED  METALLIC  PLATES. 

a  higher  grade  is  rarely  required  on  other  than  aesthetic  grounds. 
As  twenty-two  earat,  or  where  rigidity  is  recjuired,  eoin  gold  have 
become  generally  accepted  standards  for  crown-and  bridge-work, 
simplicity  will  be  consulted  by  accepting  either  of  these  as  the 
higher  grade  for  plate  work.  'J'he  choice  of  alloying  metals  is 
limited  to  silver,  copper,  and  platinum.  Silver  merely  cheapens  the 
metal;  beyond  changing  its  color,  it  alters  its  physical  properties  so 
little  that  foil  of  a  silver  and  gold  alloy  twenty  carats  fine  has  been  suc- 
cessfully used,  experimentally,  for  filling  teeth.  Silver  alone  not  only 
fails  to  impart  a  desirable  rigidity,  but  it  imparts  an  objectionable 
"brassy"  appearance,  and  the  alloy  does  not  take  the  polish  and  pleas- 
ing color  associated  with  gold.  Copper,  when  used  alone  imparts  rigid- 
ity in  too  great  a  degree;  it  also  gives  to  the  alloy  a  reddish  hue.  While 
the  alloy  takes  a  high  polish,  and  has  a  rich  color,  it  soon  tarnishes 
in  the  mouth  and  assumes  an  objectionable  copper  color.  The  tw^o 
metals  combined  in  proper  proportions  impart  to  the  alloy  a  desirable 
strength  and  color.  The  purity  of  the  metals  in  the  alloy  is  an  impor- 
tant consideration.  Commercially  pure  gold  and  silver  are  readily 
obtained  from  refiners  of  the  precious  metals,  and  should  always  be 
used  instead  of  coin  in  making  gold  plate.  The  generally  accepted 
idea  that  coin  is  a  reliable  source  of  the  precious  metals  is  an  error. 
The  mint  standard  is  fixed  only  as  regards  the  product  as  a  medium  of 
commercial  exchange;  this,  and  the  wearing  properties  of  the  coin 
are  alone  considered.  The  pure  metals  are  more  reliable,  and  are  no 
more  costly.  Commercial  copper  is  an  unknown  quantity;  it  and  its 
various  alloys,  should  be  rigidly  excluded,  and  chemically  pure  copper 
obtained  from  dealers  in  fine  chemicals,  prepared  expressly  for  chemical 
usage,  used  in  its  stead.  ^Yhile  the  difference  in  cost  is  very  great,  the 
small  amount  used  makes  the  item  insignificant. 

The  following  formulas  will  meet  all  requirements  of  dental  plate 
work: 

Gold  Plate  18  Carats  Fine. 

Pure  gold 18  parts, 

Pure  silver 4  " 

Pure  Copper 2  " 

Gold  Plate  22  Carats  Fine. 

Pure  gold 22  parts, 

Pure  Silver 1  " 

Pure  Copper 1   " 

If  greater  rigidity  is  desired,  from  one-half  part  to  one  part  of  silver 
may  be  replaced  with  platinum  in  either  formula. 

Gold  Plate  for  Clasps,  18  Carats  Fine 

Pure  Gold 18  parts 

Pure  Silver 2  " 

Pure  Copper 2  " 

Platinum 2  " 

The  alloy  for  clasps  may  be  used  for  clasps  on  either  eighteen  or 
twenty-two  carat  plates,  the  fusing  point  is  sufficiently  high  to  permit 
the  use  of  twenty-two  carat  solder,  and  the  difference  in  color  between 


SWAGED  METALLIC  PLATES.  551 

this  and  a  higher  carat  containing  sufficient  platinum  to  impart  the  re- 
quired eUisticity  is  not  objectionable.  It  may  also  be  used  with  ad- 
vantage for  making  the  backings  for  all  eighteen  carat  gold  dentures  on 
account  of  its  greater  strength,  and  for  reinforcing  partial  dentures 
for  either  the  upper  or  the  lower  jaw. 

Silver  plate  is  the  900-fine  alloy  of  silver  and  copper  known  as  coin 
silver.  Pure  silver  is  too  soft  and  inelastic  used  alone.  Since  the  ad- 
vent of  vulcanite  it  is  now  seldom  used.*  While  in  most  mouths  it  is 
quickly  discolored,  and  in  a  few  exceptional  cases  is  corroded  and  dis- 
solved, it  serves  a  good  purpose  when  a  metallic  plate  is  required  and 
the  expense  of  gold  is  objectionable.  Coin  silver  plate  is  not  quite  as 
rigid  as  eighteen  carat  gold,  and,  therefore,  must  be  made  consider- 
ably thicker.  It  is  somewhat  easier  to  work  than  gold,  but  requires 
more  care  to  avoid  overheating  in  annealing  and  soldering,  and  it  is 
well  to  remember  that  it  is  readily  and  quickly  dissolved  in  boiling 
sulphuric  acid.  The  dilute  acid  used  as  "pickle,"  is  frequently  heated 
to  expedite  the  process  of  cleansing  a  case  after  soldering.  It  is 
quite  safe,  provided  the  acid  is  not  too  strong,  and  the  boiling  is  not 
continued  too  long.  When  this  "pickle"  is  boiled,  the  water  is  eva- 
porated more  rapidly  than  the  acid,  and  a  time  comes  when  it  reaches 
a  concentration  that  dissolves  silver  as  quickly  as  does  its  proper 
solvent,  nitric  acid.  It  is  a  wise  precaution,  therefore,  to  allow  the 
silver  to  remain  in  the  acid  solution  only  sufficiently  long  to  accomplish 
the  cleansing. 

A  suitable  alloy  for  silver  plates  is  made  by  adding  to  pure  silver  one- 
tenth  its  weight  of  pure  copper.  Attempts  have  been  made  to  improve 
this  alloy  by  adding  platinum  or  iridium.  If  these  costly  metals  are 
added  in  sufficient  quantity  to  materially  increase  the  strength  or  dura- 
bility of  the  alloy,  it  becomes  as  expensive  as  gold,  while  far  inferior  to 
gold  as  a  base  for  an  artificial  denture. 

Alloys  of  gold  and  of  silver,  containing  a  small  portion  of  zinc  to  re- 
duce the  fusing  point,  are  used  as  solders  to  unite  the  various  parts  of  a 
finished  denture.  It  is  commonly  asserted  that  zinc  makes  with  gold 
a  brittle  alloy;  this  is  true  only  of  the  impure  commercial  zinc,  and  is 
due  in  all  probability  to  some  impurity  it  contains  rather  than  to  the 
metal  itself.  Chemically  pure  zinc  may  be  added  to  alloys  of  gold  and 
of  silver  in  sufficient  amount  to  produce  freely  flowing  solders  without 
impairing  materially  their  ductility,  while  a  few  grains  of  filings  from  a 
zinc  die  are  at  times  quite  sufficient  to  make  an  ingot  of  gold  weighing 
several  ounces  so  brittle  as  to  break  like  a  piece  of  crockery  when 
struck  with  a  hammer.  The  only  grade  of  zinc  admissible  for  making 
gold  and  silver  solders  is  that  known  as  "strictly  chemically  pure." 
All  formulas  calling  for  brass,  spelter,  or  other  zinc  and  copper  alloys 
should  be  discarded,  these  alloys  are  of  uncertain  composition,  and  in 
addition  contain  many  injurious  impurities.  The  following  formulas 
are  sufficient : — 

1  The  writer  has  recently  met  with  a  case  where  a  vulcanite  plate  could  not  be  worn  on  ac- 
count of  its  irritating  the  surface  with  which  it  was  in  contact.  Two  gold  plates  were  made, 
differing  in  size  and  mode  of  support,  which  proved  quite  as  uncomfortable.  A  silver  plate  was 
next  tried,  and  proved  quite  satisfactory,  and  is  worn  with  comfort. 


552  SWAGED  METALLIC  PLATES. 

Eighteen  Carat  Gokl  Solder. 

Pure  Gold 18   parts 

Pure  Silver 3  " 

Pure  Copper 2" 

Pure  Zinc li" 

Twenty-two  Carat  Gold  Solder. 

Pure  Gold 22  parts, 

Pure  Copper 1  part. 

Pure  Zinc li  parts. 

Silver  Solder. 

Pure  Silver 19  parts, 

Pure  Copper 1  part. 

Pure  Zinc  ' 4    parts. 

Some  little  care  and  dexterity  are  required  to  get  into  the  alloy  the 
full  amount  of  zinc.  Zinc  is  not  only  readily  oxidized  at  the  temperature 
at  which  the  noble  metals  melt,  Ijut  it  is  also  volatilized.  No  flux 
will  prevent  this.  The  noble  metals  are  first  brought  to  full  fusion,  the 
crucible  containing  them  is  taken  from  the  furnace,  the  zinc  dropped  in, 
and  after  a  quick  dexterous  shake,  its  contents  are  immediately  poured 
into  the  ingot.  Before  rolling  the  ingot  it  may  be  tested  by  breaking 
off  a  small  portion  from  a  corner.  The  eighteen  carat  gold  solder 
should  flow  freely  upon  a  piece  of  silver  plate  of  about  26  gauge;  the 
twenty-two  carat  may  be  tested  in  like  manner  upon  a  piece  of  eighteen 
carat  plate;  and  the  silver  solder  should  freely  flow  upon  silver  plate. 
Solders  made  from  the  above  formulas  will  do  this  if  properly  made. 
There  is  no  necessity  for,  and  no  advantage  in  using  solders  of  a  lower 
carat  than  the  plate  for  new  work.  There  is  ample  margin  between 
the  fusing  point  of  the  above  solders  and  the  same  carat  plate  to  permit 
their  safe  use  with  ordinary  care.  A  sixteen  carat  gold  solder  may  at 
times  be  needed  for  repair  work,  for  other  purposes  it  should  have  no 
place  in  a  dental  laboratory.  Solders  should  be  rolled  to  about  No.  28 
(Brown  and  Sharp  gauge). 

In  manipulating  gold  and  silver,  they  must  be  frequently  annealed 
by  being  heated  to  a  dull  red  heat  and  plunged  into  cold  water.  Under 
manipulation  they  soon  become  inelastic  and  obdurate,  and  must  be 
reannealed  as  soon  as  this  condition  is  re-established.  There  is  no  ad- 
vantage in  annealing  at  a  very  high  heat,  but  on  the  contrary,  there  is 
S3rious  risk  of  overheating,  especially  with  silver.  If  either  metal  is 
allowed  to  become  so  hot  as  to  be  fused  upon  the  surface,  it  is  not  only 
roughened,  but  the  texture  of  the  metal  is  in  a  measure  destroyed.^ 

Particles  of  base  metal  must  be  kept  from  the  surface  of  gold  or  silver; 
a  particle  of  lead,  tin,  or  zinc  will,  when  heated,  form  with  the  metal 
underlying  it  a  brittle  alloy  melting  at  a  low  temperature,  so  that  when 
the  plate  is  again  heated  a  hole  is  burned  through  at  that  point.  The 
hard  rubbing  which  necessarily  occurs  between  the  dies  and  the  ptate 

1  Xotwithstaudlng  the  large  proportion  of  zinc— if  the  zinc  is  pure— this  solder  is  free  from 
brittleness  and  keeps  its  color  in  the  mouth. 

2  It  is  possible  to  produce  blisters  on  sterling  silver  by  overheating  it  during  annealing  in  an 
oxidizing  atmosphere.  It  is  generally  assumed  that  blisters  are  a  fault  in  the  metal  itself,  and 
are  caused  by  imperfect  melting.  Experiments  show  that  sterling  silver  cannot  be  blistered 
when  a  reducing  flame  is  used  in  annealing,  but  an  oxidizing  flame  produces  numerous  blisters, 
due  to  the  silver  absorbing  oxygen  when  the  temperature  approaches  the  melting-point. 


FORMING   THE  PATTERN.  553 

during  the  process  of  swaging  imparts  to  the  plate  a  thin  film  of  base 
metal;  if  this  is  permitted  to  remain  when  the  plate  is  annealed,  while 
it  may  not  be  in  sufficient  amount  to  immediately  cause  a  hole,  it  may 
so  impair  the  texture  of  the  metal  that  later  a  hole  suddenly  appears 
either  from  rupture  or  fusion.  To  avoid  this  the  plate  should  be 
"pickled,"  that  is  placed  into  a  bath  of  sulphuric  acid  and  water  to  re- 
move any  particles  of  base  metal  immediately  before  annealing.  This 
should  be  done  before  it  is  annealed  every  time  the  plate  is  swaged,  or 
brought  in  contact  with  the  metal  dies.  The  "pickle"  acts  more 
promptly  and  certainly  if  it  is  heated  to  near  its  boiling  point;  other- 
wise a  few  minutes  must  be  allowed  for  the  acid  bath  to  do  its  work. 
Careful  attention  to  these  little  matters  will  save  a  great  deal  of  trouble 
and  annoyance  at  a  later  stage  of  the  work. 

FORMING  THE  PATTERN. 

The  first  step  in  constructing  a  plate  is  the  important  detail  of  mak- 
ing a  pattern  to  serve  as  a  guide  in  cutting  to  the  required  dimensions 
the  metal  of  which  the  plate  is  to  be  made.  This  may  seem  a  simple 
and  unimportant  matter,  but  a  little  experience  will  prove  that  this  is 
not  the  case.  Apart  from  economy  in  working  with  the  precious  metals, 
having  the  form  from  which  the  plate  is  to  be  made  of  exact  size  and 
shape,  especially  for  partial  and  full  lower  plates,  is  not  only  a  saving 
of  time  but  enables  the  workman  to  produce  a  better  result  than  when 
cut  to  a  faulty  pattern,  for  then  the  metal  must  be  strained,  and  often 
torn,  in  adapting  it  to  the  dies.  It  should  be  made  exactly  to  the  lines 
drawn  on  the  cast  to  indicate  the  extent  of  the  plate.  This  pattern 
may  be  made  of  thin  sheet  lead,  or  heavy  tin-foil,  or  a  rather  soft  paper, 
such  as  is  used  for  newspapers,  for  instance.  If  lead  or  tin  is  used,  the 
pattern  should  be  formed  on  the  die  to  avoid  bruising  the  plaster  model. 
The  pattern  metal  is  laid  upon  the  die,  and  by  the  fingers  is  pressed  • 
into  the  deeper  portions  of  the  die;  the  rubber  tip  of  a  lead-pencil,  a 
wad  of  soft  paper,  or  a  burnisher  is  then  used  to  secure  a  closer  adapta- 
tion. When  the  pattern  has  been  made  to  conform  to  the  die,  it  is  re- 
moved to  the  model  and  accurately  trimmed  to  the  plate  lines.  If  paper 
is  used,  all  the  work  may  be  safely  done  upon  the  model.  The  writer 
much  prefers  to  make  the  pattern  of  paper.  With  care,  a  paper  pattern 
can  be  made  sufficiently  accurate  for  all  practical  purposes.  While 
patterns  of  tin' or  lead  can  be  more  readily  made  to  conform  to  the 
model,  they  are  much  more  difficult  to  flatten  out  without  distortion, 
especially  in  those  cases  where  distortion  causes  the  most  trouble.  In 
upper  plates,  either  partial  or  full,  there  is  but  little  trouble  in  securing 
sufficiently  accurate  results.  Where  the  palatal  vault  is  high,  it  is  nec- 
essary to  press  the  pattern  well  into  it,  or  it  will  prove  "too  small  at  the 
sides.  In  lower  cases,  partial  or  full,  it  is  very  important  that  the  pat- 
tern should  give  the  proper  curve  as  well  as  the  dimensions  of  the  plate, 
especially  so  in  cases  such  as  that  represented  by  Figs.  528  and  529.  At 
best,  such  plates  are  difficult  to  make,  and  any  inaccuracy  in  the  curve 
of  the  pattern  will  give  a  great  deal  of  additional  trouble.     The  usual 


554  s]\'A(;ki)  metallic  plates. 

tciidc'iicy  is  to  make  tlic  j)atttTii  too  straight — not  curxcd  enough — 
owing  to  the  pattern  not  being  properly  adapted  at  its  hngual  aspect 
when  the  sides  are  trimmed,  or  to  its  being  stretched  out  of  shape  when 
it  is  flattened  out.  Figs.  5.^0  and  51^1  will  give  a  general  idea  of  the  form 
such  a  pattern  shonld  ha\e  for  the  plate  represented  in  Figs.  528  and  529. 
Patterns  for  any  additional  pieces  of  metal  that  may  be  needed  to  com- 
plete, the  plate  should  be  made  at  the  same  time.  If  for  an  upper  plate 
with  a  soldered  chamber,  a  pattern  for  this  will  be  required,  about  one- 
eighth  inch  larger  on  all  sides  than  the  base  of  the  chamber.  Occasion- 
ally it  is  best  to  extend  the  back  margin  of  the  chamber-piece  to  the 
margin  of  the  plate,  or  if  the  distance  from  tuberosity  to  tuberosity  is 
excessive,  this  covering  piece  may  be  extended  at  the  angles,  forming 
buttresses  to  the  plate,  as  shown  by  dotted  lines  in  Fig.  532.  If  the 
plate  is  to  be  double,  both  pieces  of  metal  may  be  cut  by  the  same  pat- 
tern. Partial  lower  plates  require  a  reenforcing  piece  across  the  space 
occupied  by  the  natural  teeth,  and  to  about  half  an  inch  beyond  on  each 
side,  and  in  some  cases  where  the  plate  at  this  point  is  narrow,  or  the 

Fig.  528 


Partal  lower  plate  supporting  jiosterior  teeth  only. 


space  is  long,  a  third  piece,  somewhat  smaller,  preferably  made  of  plat- 
inous  gold  if  the  plate  is  of  gold,  will  be  required  to  ensure  sufficient 
strength  and  stiffness.  It  is  desirable  that  all  the  patterns  should  be 
made  before  attempting  to  cut  the  metal,  as  it  frequently  happens  that 
they  can  be  fitted,  the  one  beside  the  other,  so  as  to  economize  the 
stock  from  tvhich  they  are  cut. 

PREPARING  THE  METAL  FORM. 

The  thickness  of  the  metal  for  a  dental  plate  is  governed  by  the  size 
and  shape  of  the  intended  denture.  A  very  small  plate  can  be  safely 
made  thinner  than  a  large  one;  a  vacuum-chamber  plate  covering  a 
small  area  of  the  palate,  compact  in  form  and  stiffened  by  its  various 


PREPARING   THE  METAL  FORM. 


555 


corrugations,  and  by  a  stamped  or  soldered  vacuum-cavity,  may  be 
made  much  thinner  than  a  narrow  chispcd  phite,  horse-shoe  in  shape. 
ApUite  for  a  fiat  moutli  shoukl  be  made  lieavier  than  one  for  a  deep  pal- 
atal vault,  or  for  a  cast  with  a  sharp  prominent  ridge.  Plates  for  the 
lower  jaw  should  be  heavier  than  those  for  the  upper,  and  a  silver  plate 


Fig.  520 


Partial  lower  plate  supporting  anterior  and  posterior  teeth. 


should  be  two  or  three  numbers  heavier  than  one  of  gold  for  the  same 
position. 

Where  great  rigidity  is  needed,  it  is  good  practice  to  make  two  thin 
plates  and  solder  them  together.  By  this  means  greater  rigidity  is  ob- 
tained than  by  a  single  plate  of  the  same  weight,  and  a  better  adapt- 

FiG.  530 


Pattern  for  a  partial  lower  plate  supporting  the  posterior  teeth  only,  like  Fig.  528.  The 
dotted  line  indicates  the  extension  of  the  metal  form  beyond  the  line  of  the  pattern,  to  allow 
for  a  portion  of  the  metal  to  be  bent  or  hooked  over  the  front  of  the  die  to  prevent  the  plate 
slipping  backward  during  swaging. 

ation  is  secured,  because  the  thinner  metal  is  more  pliable  during  swag- 
ing. For  gold  the  gauge  may  range  for  single  plates  from  about  No. 
24,  which  is  about  as  thick  as  can  readily  be  swaged,  to  about  No.  28, 
while  No.  29  or  30  is  suitable  when  two  plates  are  made  and  soldered 
together. 


55G 


SWAGED  METALLIC  PLATES. 


Ilavin<i;;(leci(l(Ml  upon  tlio  tliickno.s.s,an(l  haviiio;  rolled  the  motal  to  the 
required  gauf^e,  the  patterns  are  arran<>;e(l  side  by  side  so  that  they  may 
be  cut  from  it  with  the  least  waste.  While  the  patterns  should  be  made 
accurate,  some  little  allowance  must  he  made  when  cuttiufij  the  metal 
by  them  for  any  slight  change  in  position  the  metal  may  take  during 


Fig.  531 


PaUern  for  a  partial  lower  plate  supporting  anterior  and  posterior  teeth,  like  Fig.  a'ZX     I'l*" 
metal  form  is  cut  as  shown  by  the  dotted  lines. 

swaging.  With  all  plates  an  allowance  of  a  full  sixteenth  of  an  inch 
should  be  made  on  all  sides,  as  shown  by  the  dotted  lines  in  Fig.  532. 
The  indentations  to  accomodate  remaining  natural  teeth  should  not  be 
too  closely  followed.  An  allowance  should  be  made  in  the  front  portion 
of  forms  for  plates  like  Fig.  528,  as  shown  by  dotted  lines  in  Fig.  530,  to 
allow  for  a  portion  of  metal  to  be  bent  or  hooked  over  the  die  and  so  pre- 


FiG.  532 


The  shaded  portion  shows  the  pattern  for  a  partial  vacuum  plate  where  the  natural 
canine  teeUi  alone  remain.  The  inner  doited  line  tlie  paltern  tor  the  vacuum-chamber 
cover  as  ordinarily  made,  and  as  It  should  be  when  extended  to  the  tuberosities  to  give 
rigidity  to  wide,  flat  plate. 

vent  the  plate  changing  its  position  during  swaging.  The  writer  pre- 
fers to  make  these  allowances  when  cutting  the  metal  form  rather  than 
when  making  the  pattern;  if  the  pattern  shows  the  size  absolutely 
needed,  by  fitting  one  pattern  with  another  or  by  reducing  the  allowance 
at  immaterial  points,  the  plate  can  be  cut  more  economically.    x\t  places 


PREPARING  THE  METAL  FORM.  557 

representing  the  necks  of  the  teeth  tlie  phite  shoukl  always  be  cut  with 
a  rounded,  never  with  an  anguhir  outHne.  The  phate  is  unavoidably 
subjected  to  considerable  strain  during  the  swaging  process;  this  is  apt 
to  start  a  break  or  tear  at  any  point  of  its  periphery  weakened  by  a  slight 
cut  or  angular  indentation.  A  greater  surplus  is  allowed  with  partial 
lower  plates  to  compensate  for  the  greater  danger  of  displacement  in 
swaging;  as  they  are  very  apt  to  slip  to  one  side  or  the  other,  especially  at 
that  portion  covering  the  distal  portion  of  the  ridge,  it  is,  therefore,  wise 
to  make  the  form  a  little  wider  at  this  point  than  the  pattern  calls  for. 
\Yhile  it  is  well  to  remember  that  gold  plate  depreciates  very  much  in 
value  when  reduced  to  scraps,  it  is  not  wise  to  cut  so  closely  to  the  pat- 
tern as  to  risk  losing  valuable  time  in  accurately  adjusting  the  form 
within  the  plate  lines,  or  perhaps  spoiling  the  piece  by  its  slipping  to 
one  side  beyond  recall. 

Having  laid  the  pattern  upon  the  metal  of  which  the  plate  is  to  be 
made,  selecting  a  position  where  it  can  be  cut  with  the  least  waste,  trace 

Fig.  533 


Pattern    for  a  pE.rtial   vacuum  plate  such  as  shown  by   Fig.  526.     The    metal  form  is  cut  as 
indicated  by  the  dotted  line. 

its  outlines  with  a  sharp  point  or  tracer,  and  cut  to  this  line  with  straight 
or  curved  shears  as  may  serve  best,  as  closely  as  may  be  deemed  prudent. 
In  cutting  the  form  for  a  partial  upper  plate  it  is  best  not  to  follow  the 
outlines  of  the  pattern  where  it  is  cut  out  to  fit  around  the  natural  teeth, 
but  to  leave  these  portions  to  be  removed  after  the  plate  is  partly  fitted 
to  the  die.  If  the  form  is  accurately  cut  to  the  pattern,  it  must  be 
accurately  adjusted  to  the  die — in  practice  a  very  difficult  task.  Fig. 
533  shows  the  outlines  of  the  pattern — the  dotted  line  the  size  and  shape 
to  which  the  metal  should  be  cut  for  a  plate  like  Fig.  534. 

In  cases  requiring  an  extra  rigid  plate,  or  in  cases  especially  difficult 
to  swage,  whether  to  make  a  heavy  single  plate  or  two  thin  ones  and 
solder  them  together,  is  a  matter  upon  which  there  is  a  difference  of 
opinion.  A  plate  made  of  two  laminae  thoroughly  soldered  together, 
is  undoubtedly  much  more  rigid,  and  is  usually  heavier  than  can  readily 
be  swaged  as  a  single  plate.  Apart  from  this,  the  slight  unevenness  in 
the  thickness  of  the  solder,  owing  to  the  two  plates  not  being  in  abso- 
lute contact  at  all  points,  tends  to  give  it  increased  rigidity.  Partial 
lower  plates  must  be  thus  stiffened  where  they  pass  behind  remaining 


558  SWAGED  METALLIC  PLATES. 

natural  teeth.  Practice  differs  as  to  whether  a  narrow  full  lower  plate, 
or  a  narrow  upper  clasped  plate,  horse-shoe  in  shape,  should  be  so 
made.  In  the  writer's  judgment  a  full  lower  plate  made  of  a  proper 
thickness  with  its  edges  all  around  bound  with  half-round  wire,  will 
usually  be  sufficiently  rigid  for  all  practical  purposes.  A  narrow  upper 
plate  requires  to  be  doubled  over  the  greater  part  of  its  area.  The 
writer  prefers  to  make  the  plate  heavy,  and  to  make  the  strengthening 
piece  from  one-eighth  to  one-fourth  of  an  inch  narrower  than  the  plate, 
so  as  to  leave  its  free  edges  of  a  single  thickness.  This  does  not  impair 
its  strength  or  rigidity,  while  it  permits  a  ready  bending  up  or  down  of 
these  edges  to  accommodate  those  changes  taking  place  in  the  mouth 
after  the  plate  has  been  worn,  which  require  at  times  that  the  plate  be 
made  to  fit  closer,  and  at  other  times  that  undue  pressure  upon  the  soft 
tissues  be  relieved.    There  are  certain  points  in  all  partial  plates  to  be  in- 

FiG.  5:14 


Partial  vacuum  plate  to  support  several  isolated  teeth. 

dicated  later,  which  are  especially  liable  to  fracture,  and  which  re- 
quire additional  strength  beyond  that  necessary  to  make  the  plate 
suflBciently  rigid  to  retain  its  shape  when  subject  to  the  wear  and  tear 
of  actual  use.  The  resistance  of  the  dies  limits  the  thickness  of  plate 
liiat  may  be  used.  If  to  make  a  plate  thoroughly  strong,  calls  for  a 
greater  thickness  than  can  be  readily  and  accurately  swaged,  a  double 
plate  is  required. 

MAKING  THE  PLATE. 

The  sheet  metal  form  is  annealed  by  being  heated  all  over  to  a  dull  red 
heat,  being  careful,  however,  especially  when  working  with  silver,  that 
it  is  not  made  so  hot  as  to  be  "burned"  or  "sweated;"  that  is,  fused 
on  the  surface.  When  this  has  been  done  the  plate  is  not  only  rough- 
ened, but  its  texture  is  destroyed,  and  it  becomes  in  a  measure  brittle. 
It  is  a  matter  of  no  moment  whether  the  plate  is  cooled  quickly  or  slowly 


MAKIXG  THE  PLATE.  559 

after  annealing;  it  is  usually  plunged  into  cold  water  to  save  time.  It 
should  be  annealed  every  time  it  is  swaged:  before  doing  so  it  should  be 
placed  for  a  few  minutes  in  a  bath  of  equal  parts  of  sulphuric  acid  and 
water,  or  a  boiling  solution  of  alum,  technically  termed  "pickle,"  to  re- 
move any  particles  of  base  metal  that  may  have  adhered  to  or  become 
attached  to  it.  If  these  are  allowed  to  remain,  when  the  plate  is  heated 
they  become  alloyed  with  it,  and  either  produce  a  roughness,  or  a  hole, 
according  to  the  amount  present. 

There  is  but  little  difference  between  the  manipulation  of  gold  and 
silver  in  making  a  plate,  except  that  gold,  being  stiffer  and  becoming 
hard  sooner,  requires  a  little  more  manipulation  and  more  frequent 
annealing  than  silver. 

Making  a  Plate  for  a  Full  Upper  Denture. — The  poorer  die  is  cleansed 
by  brushing  off  any  particles  of  sand  or  metal ;  any  inaccuracies  are  cor- 

FiG.  535 


Horn  or  wooden  mallet,  used  to  adapt  the  metal  form  to  the  die  preparatory  to  swaging. 

rected,  and  any  roughness  not  shown  on  the  model  made  smooth.  Place 
it  upon  a  portion  of  the  work-bench,  where  it  will  rest  solidly  and  firmly, 
or,  better  still,  hold  it  in  the  jaws  of  a  bench  vise,  the  back  part  toward 
the  workman.  Have  the  plaster  model  near  at  hand  so  that  the  posi- 
tion and  extent  of  the  plate  may  be  seen  at  a  glance.  Now  place  the 
annealed  form  on  the  die,  having  jQrst  smoothed  or  rounded  any  sharp 
points  left  by  the  shears  that  might  cut  the  hands,  and  note  the  position 
in  which  it  will  best  cover  the  outlines  of  the  plate.  Holding  it  firmly 
in  position  with  the  left  hand,  with  a  horn  or  wooden  mallet  (Fig. 
535)  held  in  the  right,  bend  down  the  outer  edge  with  light,  rapid 
blows,  being  careful  that  the  position  of  the  plate  is  such  that  it  will  ex- 
tend over  the  ridge  far  enough  to  meet  the  lines  drawn  on  the  cast, 
and  also  allow  for  the  sides  to  be  drawn  in  when  the  plate  is  swaged 


500  SWAGED  METALLIC  PLATES. 

into  the  palatal  arch.  It  is  not  desired  at  this  stage  to  make  the  edge 
fit  closely  to  the  die,  but  simply  to  give  it  a  downward  tendency,  so 
that  when  the  mallet  is  used  to  drive  the  centre  down,  the  tendency  of 
the  plate  to  slide  backward  will  be  checked,  while  the  edges  being  thus 
bent,  will  at  the  same  time  naturally  be  drawn  closer  to  the  die.  If 
the  centre  of  the  plate  should  be  fitted  first,  the  edges  will  naturally 
flare  up;  the  effort  to  bring  them  into  position  would  not  only  tend  to 
again  straighten  the  centre  of  the  plate,  but  also  to  stretch  and  throw 
the  outer  edge  into  folds  or  creases.  "When  once  this  movement  has 
started,  it  is  very  difficult  to  control;  the  pounding  necessary  to  work 
out  these  folds  will,  by  stretching  the  plate,  increases  the  difficulty. 

It  is  best,  especially  in  deep  mouths,  to  work  the  plate  well  down  to 
the  centre  of  the  die  with  the  mallet  before  using  the  counter-die.     The 
skilful  use  of  the  mallet  "draws"  the  metal  into  place;  it  is  free  to  slide 
over  the  ridges  as  it  is  bent  dow^n  into  the  die  by  the  mallet;  as  soon  as 
the  counter-die  is  used,  that  portion  of  the  plate  over  the  ridge  becomes 
"set"  and  does  not  so  readily  "draw  in"  to  the  concavity  of  the  die. 
The  metal  is  stretched,  and  in  very  deep  mouths  the  plate  may  be  split 
if  the  counter-die  is  used  too  soon.     The  mallet  should  be  held  lightly 
between  the  thumb  and  fingers,  not  grasped  in  the  hand,  and  the  blows 
struck  should  l)e  light,  rapid,  and  springy;  otherwise  the  plate  becomes 
battered  and  bruised.     Some  workmen  prefer  to  fit  the  plate  into  the 
palatal  portion  of  the  die  by  the   use  of  partial  counter-dies,  that  is, 
counter-dies  made  to  fit  into  the  palatal  portion  of   the  die  only, 
and  not  extending  over  the  ridge.     A  series  of  these  are  recjuired,  be- 
ginning with  one  taking  in  the  middle  portion  of  the  palate  only,  each 
succeeding  one  extending  further  toward  the  ridge.     During  this  pro- 
cess the  plate  will  require  frequent  annealing,  always  preceded  by  a 
l)ath  in  the  pickle.     After  the  plate  has  been  fitted  as  well  as  it  can  be 
with  the  mallet,  place  it  on  the  die,  first  covering  the  face  of  the  die  with 
several  thicknesses  of  thin  paper,  cloth,  such  as  comes  with  vulcanized 
rubber,  or  a  rubber  dam,  and  placing  a  like  covering  of  paper  over  the 
plate,  accurately  adjust  them  to  the  counter-die.     At  this  early  stage 
of  the  swaging  there  is  more  rulibing  between  the  metal  and  the  dies 
than  later,  and  this  paper  not  only  protects  the  plate  from  the  base 
metals  of  the  dies,  but  saves  it  from  being  bruised  and  roughened. 
Place  the  die  and  counter-die,  with  the  plate  between  them  on  the  anvil, 
with  the  counter-die  down,  and  while  grasping  the  die  with  the  left  hand, 
holding  it  firmly  in  place,  strike  it  a  light  blow  with  the  large  hammer. 
Now  examine   and  make  sure  that  the  plate  has  not  moved,  as  it  is  apt 
to  do,  then  holding  it  as  before,  strike  several  moderately  heavy  blows. 
It  is  desired  at  this  stage  to  simply  fix  the  plate  in  position.     Remove 
it  from  the  dies,  pickle  and   anneal  it.     In  using  the  swaging  hammer 
grasp  the  handle  near  the  head  of  the  hammer,  and  strike  deliberately, 
firndy  holding  the  hammer  down  so  as  to  prevent  any  rebound.     If 
the  hammer  is  allowed  to  rebound,  as  it  tends  to  do,  the  die  follows, 
and   in  setding  down   again,  is  apt  to  slightly  change  its  position. 
It  requires  very  few  of  such  blows  to  produce  a  plate   no  one  can 


^fAR'^XG    THE  PLATE.  561 

make  fit  the  model  accurately.  The  character  of  the  force  used  in  swag- 
ing is  a  matter  of  great  importance,  not  only  in  making  a  plate  to  fit,  but 
also  in  making  a  plate  that  will  not  change  its  fit  in  subsec[uent  opera- 
tions. The  nearer  the  hammer  blows  resemble  those  of  a  drop- 
press,  or  a  pile  driver,  the  more  effective  they  will  be.  If  it  were 
practicable  to  make  dies  and  counter-dies  suitable  for  it,  a  screw  or 
hydraulic  press  would  be  ideal  for  swaging  dental  plates. 

Now,  examine  first  if  the  plate  is  in  a  position  to  well  cover  all  the 
Hues;  next  note  if  there  are  any  wrinkles  or  creases  on  the  palatal  portion 
of  the  plate.  With  some  forms  of  palatal  vault  they  are  apt  to  occur  at 
the  posterior  edge  of  the  plate,  and  should  be  promptly  straightened 
with  the  mallet.  Then  see  that  the  plate  is  well  down  to  the  die  at  the 
central  portion  of  the  palate.  At  times  this  first  swaging  tends  to  draw" 
the  plate  up,  especially  so  if  the  counter-die  extends  too  far  over  the  die. 
If  the  plate  does  not  fully  cover  all  the  lines,  its  position  can  be  changed 
at  this  stage  by  bending  with  the  mallet.  It  is  important,  before  pro- 
ceeding further,  to  make  the  palatal  portion  of  the  plate  fit  closely  to 
the  die,  using  the  mallet  to  drive  it  down  if  necessary.  The  portion 
extending  over  the  ridge  next  requires  attention.  First  straighten  out 
any  T\Tinkles  that  may  have  formed,  and  make  the  plate  fit  as  closely  as 
possible  the  outer  portion  of  the  alveolar  ridge.  To  facilitate  this,  cut  off 
with  the  shears  any  surplus  portions  of  the  plate  that  extend  to  a  marked 
degree  over  the  fines,  remembering,  however,  when  so  doing,  that  the 
tendency  of  further  swaging  may  be  to  draw  these  edges  up.  In  some 
plates  it  is  necessary  to  remove  a  V-shaped  section  at  the  frsenum  be- 
fore they  will  lie  close  along  the  outer  portion  of  the  ridge;  it  should  not 
be  done,  however,  at  this  stage.  During  these  manipulations  w^henever 
the  plate  becomes  rigid  and  unyielding,  it  should  be  annealed.  When  the 
plate  has  been  made  to  fit  well  as  it  can  be  with  the  mallet,  it  is  annealed 
and  again  swaged  between  the  dies,  using  paper  or  cloth  on  each  side  as 
before.  After  a  few  light  blows,  separate  the  dies  sufficiently  to  see  that 
the  plate  has  not  changed  in  position;  if  found  satisfactory  in  this  re- 
spect, it  should  now  receive  a  thorough  swaging,  moving  the  dies  around 
with  the  left  hand  and  striking  hea\y  blows  over  successive  portions  of 
the  die. 

Attention  is  now  given  to  the  vacuum-ca\ity.  If  it  is  of  the  Gilbert 
pattern,  swaged  with  the  plate,  two  special  tools  are  needed  to  give  it  a 
sharp  outline,  and  to  make  it  fit  at  its  edges  close  to  the  roof  of  the 
mouth.  First  is  a  chaser  made  of  bone.  This  may  be  made  of  a  tooth- 
brush handle,  one  end  of  which  is  filed  to  a  moderately  sharp,  smooth 
chisel-like  edge,  rounded  at  its  corners,  and  about  one-fourth  of  an  inch 
wide.  This  edge  ^\*ill  require  frequent  rene■u^ng,  as  it  is  soon  battered 
by  use.  It  is  used  by  placing  the  edge  of  the  chaser  in  the  imprint  of 
the  chamber  while  the  plate  is  on  the  zinc  die,  and  holding  it  at  a  slight 
angle  as  one  would  a  chisel  in  cutting  a  groove,  striking  light  rapid  blow^s 
on  the  end  with  a  mallet  or  bench  hammer,  so  as  to  drive  it  down  and 
forward.  Pass  it  round  the  chamber  in  this  way  repeatedly,  so  as  to 
coax  the  metal  into  place. 

36 


5()2  SWAGED  METALLIC  PLATES. 

Jf  the  blows  are  struck  too  hard,  the  chaser  will  indent  the  plate, 
and  the  indentations  once  made,  are  very  difficult  to  remove.  In  some 
cases  this  bone  chaser  will  complete  the  vacuum-chamber.  If  greater 
sharpness  of  outline  is  desired,  it  is  followed  by  a  steel  chaser  with  a 
thinner,  but  well  rounded  smooth  edge,  polished  like  a  burnisher. 
This  is  used  in  the  same  manner,  but  with  caution.  If  used  to  excess 
it  may  cut  a  groove  that  must  be  filled  with  solder  to  make  a  neat  finish. 
This  chasing  of  the  vacuum-chamber  is  only  partly  finished  on  the  first 
die;  it  is  completed  after  the  plate  has  been  lightly  swaged  on  the  second 
or  finishing  die.  During  the  process,  the  plate  must  be  frequently  an- 
nealed. If  a  soldered  vacuum-chamber  istlesired,  and  the  form  for  the 
chamber  has  been  cast  on  the  die,  the  proceedure  is  somewhat  different. 
An  opening  is  cut  in  the  plate  corresponding  to  the  chamber,  but  not  to 
its  full  size  at  this  stage.  Until  the  plate  has  been  thoroughly  swaged 
on  the  second  or  finishing  die  there  is  a  possibility  of  its  slightly  chang- 
ing its  position,  for  this  reason  accurate  fitting  to  plate  lines  is  deferred 
until  that  time.  Roughly  cutting  off  the  surplus  plate  with  the  shears, 
chasing  the  chamber,  or  cutting  the  opening  for  a  soldered  chamber, 
no  matter  how  carefully  done,  distort  the  plate  to  some  extent;  there- 
fore, all  this  should  be  done  before  commencing  to  make  the  plate  fit 
the  model  accurately.  The  final  fitting  to  the  plate  line  is  readily  done 
with  the  file  without  risk  of  bending  the  plate,  and  at  the  time  this  is 
done,  the  opening  for  the  chamber  is  enlarged  until  it  exactly  coincides 
with  the  base  of  the  wax  chamber  on  the  cast.  A  covering  piece  is  then 
swaged  up  as  sharply  as  can  be  done  with  the  dies;  it  is  not  necessary 
to  use  the  chasers.  This  is  then  trimmed  all  round  to  leave  a  margin 
of  about  one-sixteenth  of  an  inch;  if  it  is  desired  that  this  margin 
should  be  well  defined  on  the  finished  plate,  the  edge  is  filed  square;  if 
on  the  contrary  this  is  not  desired,  it  is  filed  from  the  under  side  to  a 
feather  edge.  In  some  cases  the  back  edge  of  this  covering  piece  is  ex- 
tended to  the  plate  line,  not  alone  for  additional  strength,  but  to  increase 
the  thickness  at  this  point  to  provide  for  filing  from  the  underside  to  re- 
lieve pressure  upon  the  hard  palatal  ridge.  Again,  in  a  very  broad 
mouth,  the  covering  piece  may  be  extended  toward  the  tuberosities  to 
give  stiffness  and  rigidity  to  the  plate. 

Instead  of  making  a  wax  model  of  the  chamber  on  the  plaster  model 
and  reproducing  it  on  the  die,  a  better  result  is  obtained  by  making  the 
model  of  the  chamber  in  copper  or  brass  as  thick  as  the  chamber  is  in- 
tended to  be  deep.  A  piece  of  copper  or  brass  of  proj)er  thickness  is 
fitted  by  means  of  the  bench  hammer  into  the  first  die  in  the  position  of 
the  desired  chamber,  held  in  place  by  a  little  adhesive  wax,  and  swaged 
between  the  die  and  counter-die.  As  this  usually  changes  its  position 
it  should  be  sufficiently  large  to  well  cover  the  lines  of  the  chamber 
notwithstanding  this,  so  that  when  it  is  shaped  it  will  accurately  fit  the 
die  in  the  position  marked  for  it  on  the  cast.  This  is  done  with  the  first 
die  and  counter-die.  It  is  then  made  the  desired  shape  and  size,  and 
the  edges  are  smoothly  finished  with  a  slight  bevel.  An  expert  work- 
man has  no  diflSculty  in  attaching  this  to  the  finishing  die  with  adhesive 


MAKING  THE  PLATES.  563 

wax  and  swaging  it  into  the  counter-die  so  as  to  produce  in  the  counter- 
die  a  depression  into  which  the  covering  piece  is  swaged.  There  is, 
however,  a  marked  tendency  in  the  chamber  model  to  shde  backward 
or  sidewise,  to  prevent  which  the  writer  is  accustomed  to  tack  it  to 
the  plate,  whether  of  gold  or  of  silver,  with  the  least  possible  mite  of 
silver  solder.  It  can  be  readily  held  in  position  on  the  plate  with  a 
wire  clamp  while  this  is  being  done.  By  this  expedient  all  risk  of 
change  in  position  is  obviated,  and  after  it  has  been  swaged  so  as  to  make 
an  impression  in  the  counter-die,  by  inserting  a  point  under  its  edge,  and 
heating  the  plate,  the  chamber  model  is  released.  The  impression 
made  in  the  counter-die  requires  deepening  by  means  of  flat 
gravers  before  swaging  the  covering  piece.  This  method  has  the 
advantage  that  making  the  sand  mold  is  not  complicated  by  the  pres- 
ence of  the  chamber  model;  it  also  avoids  bending  up  the  edges  of 
the  chamber  when  swaging  the  plate.  The  plate,  the  chamber  model, 
and  the  covering  piece  fully  finished  and  ready  to  solder  in  place,  can 
be  swaged  between  the  die  and  counter-die  at  the  same  time,  making 
a  close  and  easily  soldered  joint.  The  opening  in  the  plate  is  roughly 
cut  when  the  finishing  counter-die  is  ready  for  swaging  the  covering 
piece,  and  is  finally  enlarged  and  shaped  just  before  the  cover  is  sol- 
dered in  place. 

After  the  plate  has  been  well  swaged  to  the  first  die,  and  roughly 
shaped  to  the  plate  lines,  especial  attention  is  given  to  that  portion  ex- 
tending over  the  alveolar  ridge.  As  a  rule,  the  extreme  edge  of  the 
plate  has  a  greater  length  than  the  plate  outline  marked  upon  the  cast; 
it  is  evident  that  to  adapt  one  to  the  other,  at  least  a  portion  of  the  sur- 
plus length  must  be  cut  out,  or  the  plate  must  be  so  manipulated  as  to 
contract  it  along  this  line,  or  else  the  amount  of  surplus  length  will  be 
represented  in  the  plate  by  wrinkles.  By  removing  the  wrinkles  by 
light  blows  with  the  horn  mallet  as  they  are  formed,  the  plate  can  be  so 
adapted  that  this  surplus  length  may  be  accomodated  by  a  slit,  or  a  V- 
shaped  piece  removed  from  the  plate  at  the  site  of  the  frsenum  of  the 
upper  lip. 

By  careful  manipulation  with  the  horn  mallet,  and  by  swaging 
with  blows  along  the  sides  of  the  counter-die,  driving  the  plate 
toward  the  die  along  the  alveolar  border,  this  slit  may  be  avoided 
in  favorable  cases.  While  this  can  seldom  be  done,  it  is  best  to 
reduce  the  wrinkling  as  much  as  possible  in  this  way;  then,  when 
the  plate  is  fairly  well  fitted  to  the  die,  to  simply  cut  a  slit 
with  the  shears  at  the  centre  of  the  plate,  extending  it  to  nearly  the 
top  of  the  ridge,  but  not  over  it.  If  it  is  cut  too  far,  the  edges 
are  apt  to  separate  at  the  apex  of  the  ridge,  leaving  a  hole  to  be  either 
filled  with  solder  or  covered  with  a  scrap  of  plate,  either  of  which  is 
objectionable.  After  making  the  cut,  bend  the  cut  edges  apart,  and 
bevel  the  opposing  sides  so  that  when  they  lap  over  they  will  make  a 
smooth  joint.  If  the  overlap  is  excessive,  it  should  be  reduced,  but  a 
liberal  overlap  is  not  objectionable.    This  slit  is  not  to  be  soldered 


564  SWAGED  METALLIC  PLATES. 

until  the  plate  is  fitted  to  the  model  and  accurately  trimmed  to  the  plate 
lines;  if  it  is  closed  too  soon,  it  may  be  impossible  to  make  the  edges  of 
the  plate  fit  the  model  as  closely  as  they  should. 

The  plate  should  be  finished  as  nearly  as  possible  upon  the  first  die. 
The  first  bending  of  the  plate  into  shape  unavoidably  subjects  the 
first  die  and  counter-die  to  an  uneven  stress;  those  i)ortions  which 
are  fir.st  brought  into  forcible  contact  with  the  plate,  together  with  the 
sharper  prominences,  become  battered.  It  is  on  this  account  that 
the  second  die  is  required.  One  careful  swaging  on  the  finishing  die 
should  be  all  that  is  needed  to  make  the  plate  fit  the  model  accurately. 
If  the  plate  has  a  soldered  chamber,  the  covering  i)iece,  fully  finished 
and  readv  to  be  soldered  in  place,  should  be  in  i)()sition  when  this  is 
done.  After  this  swaging,  make  the  outer  edge  of  the  plate  closely  fit 
the  cast  at  the  plate  line,  and  then  solder  the  front  slit.  In  many  cases 
after  this  has  been  done,  a  little  manipulation  with  the  bench  hammer 
to  bring  the  plate  in  close  contact  with  the  model  at  its  edges  is  all  that 
will  be  needed  to  make  the  plate  fit  satisfactorily. 

Testing  the  Adaptation.— To  test  the  adaptation  of  the  plate,  place 
it  on  the  plaster  model,  and  note  first  that  it  does  not  unduly  bind  on  the 
alveolar  ridge.  If  the  outer  edges  spring  in  to  the  cast  the  plate  will 
be  held  firmly  on  the  model,  although  it  may  not  fit.  While  the  edges 
must  fit  closely,  they  must  not  bind,  and  may  require  to  be  slightly 
bent  outward  to  avoid  this.  Now  see  that  it  rests  solidly  upon  the  model, 
that  it  does  not  tend  to  spring  up  when  pressed  down,  or  to  rock  when 
pressure  is  made  along  the  top  of  the  alveolar  ridge  alternately  at  the 
aides,  or  when  pressure  is  made  at  the  back  edge  of  the  plate  and  on  the 
top  of  the  ridge  at  the  sides  or  in  front.  If  the  plate  shows  no  movement 
under  tliese  tests,  if  it  has  a  swaged  chamber,  all  that  remains  to  be 
done  is  to  smooth  the  edges,  clean  and  polish  it  preparatory  to  testing 
it  in  the  mouth.  If,  however,  it  should  spring  or  rock,  the  cause  of  this 
must  be  sought  and  the  defect  corrected.  The  spring  may  be  due  to  the 
outer  edge  pressing  unduly  at  some  point,  and  holding  the  plate  from 
contact  with  the  model.  When  this  point  is  located,  a  slight  bending 
with  the  fingers  will  usually  correct  it.  It  not  unfrequently  happens 
that  the  plate  will  bind  upon  the  outer  side  of  the  tuberosity,  prevent- 
ing its  back  edge  from  fitting  solidly  to  the  model.  When  this  is  the 
case,  a  few  blows  with  the  bench  hammer  stuck  along  the  back  edge 
of  the  plate  on  each  side  just  inside  of  the  tuberosities,  while  it  is 
firmly  held  upon  the  cast,  will  usually  prove  effective.  There  is  quite  a 
"knack"  in  using  the  bench  hammer  in  giving  the  finishing  touches  to 
the  fit  of  a  plate  while  it  is  on  the  plaster  model,  so  as  to  effect  the  object 
without  bruising  the  model.  It  is  something  that  cannot  be  described, 
it  must  be  accpiired  by  observation  and  practice.  That  the  final  fitting 
needs  to  be  <lone  on  the  plaster  model  is  not  always  due  to  inaccuracy  in 
the  metallic  dies.  All  that  the  counter-die  can  do  is  to  drive  the  plate 
into  contact  with  the  die  at  the  moment  of  impact.  There  is  a  cer- 
tain elasticity  in  the  sheet  metal  of  which  the  plate  is  made  that  gives  it  a 
tendency  to  sj)ring  back  from  the  die.     Careful  annealing,  and  care- 


MAKLXG  THE  PLATE.  565 

fill  swaging  make  this  less  marked,  but  do  not  wlioUv  overcome  it.  The 
conformation  and  the  corrugations  of  the  plate  make  this  elasticity 
more  marked  at  some  points  than  at  others.  It  is  overcome  by  bending 
the  plate  at  these  points  a  little  more  than  enough;  at  times  with  the 
fingers,  at  other  times  with  the  sharp  end  or  riveting  blade  of  the  bench 
hammer,  (not  the  ball  end),  and  again  by  reswaging  with  the  die  tem- 
porarily enlarged  at  the  point  in  fault,  so  as  to  give  the  plate  a  "set," 
that  is,  bent  so  far  that  it  will  be  just  right  when  it  springs  back  and  is 
at  rest. 

Rocking  is  usually  due  to  pressure  at  some  point  inside  of  the  alveolar 
ridge.  While  it  may  be  and  is  often  due  to  some  prominent  point  of 
the  die  which  is  either  imperfect  in  the  casting  or  has  been  crushed 
during  swaging,  it  may  also  be  due  to  elasticity  of  the  plate.  The  point 
in  fault  is  usually  marked  upon  the  model  by.  a  slight  discoloration,  or  it 
may  be  located  by  closely  observing  the  movements  of  the  plate.  This 
point  having  been  determined,  place  several  thicknesses  of  thin  paper 
on  the  corresponding  point  of  the  die,  sufficient  to  make  the  plate  rock 
in  the  same  way,  but  a  little  more  than  it  does  on  the  model;  also  scrape 
away  a  little  from  the  corresponding  point  of  the  counter-die.  Now 
carefully  swage  the  plate,  holding  the  die  down  firmly  upon  the  counter- 
die,  and  striking  the  die  a  few  hard,  solid  blows,  holding  the  hammer 
down  firmly  so  that  it  does  not  rebound.  If  the  plate  now  fits  the  die 
solidly,  yet  still  rocks  upon  the  model,  the  misfit  is  probably  due  to  an  in- 
accuracy of  the  die;  the  model  may  have  been  rocked  or  tilted  when  with- 
dra-uing  it  from  the  sand  mold,  and  a  new  die  is  the  only  remedy.  Such 
defects  as  this  are  not  visible  on  the  die,  and  are  only  discoverable  dur- 
ing the  fitting  of  the  plate. 

Before  undertaking  these  manipulations,  exaruine  the  plate  system- 
atically so  as  to  determine  the  extent  and  character  of  corrections  re- 
quired. It  not  unfrequently  happens  that  some  one  correction,  in  itself 
very  slight,  will  fully  correct  an  apparently  serious  misfit,  if  it  is  at- 
tended to  first.  Observe  first,  that  the  plate  goes  on  the  model  freely; 
that  is,  that  it  is  not  necessary  to  press  it  on.  Unless  the  ridge  overhangs 
the  plate  should  fall  oft'  if  the  model  is  reversed.  Before  proceeding  fur- 
ther correct  any  binding  of  the  edges.  Xow  see  that  the  plate  is  in 
close  contact  with  all  parts  of  the  model  which  it  covers,  and  also  that  it 
does  not  press  harder  at  any  one  point  than  another.  To  do  this  hold 
the  model  in  both  hands,  the  face  up  and  the  back  part  toward  you. 
With  the  first  finger  or  thumb  of  each  hand  proceed  as  follows:  place 
the  finger  or  thumb  of  the  left  hand  on  the  little  elevation  usually  found 
on  the  ridge  immediately  in  the  front  of  the  mouth,  and  the  finger  or 
thumb  of  the  right  hand  on  the  extreme  back  edge  of  the  plate.  If 
pressing  in  front  causes  the  back  edge  of  the  plate  to  rise  from  the  model, 
or  tice  versa,  the  plate  is  said  to  "rock."  In  doing  this  it  is  very  im- 
portant that  the  pressure  be  straight  and  direct.  If  in  pressing  at  the 
point  indicated  in  the  front  of  the  mouth  the  pressure  should  be  directed 
outward,  it  would  raise  the  back  edge  of  the  plate,  although  the  plate 
might  fit  solidly;  if  it  be  directed  inward,  it  might  not  raise  it,  although 


506  SWAGED  METALLIC  PLATE. 

the  ])lat("  )iiin;lit  fit  very  iiujXM-fcctly.     This  is  a  ])(>iiit  to  he  horiK"  in 
mind. 

KiH"|)in<i;  the  lintri-r  on  the  point  in  front,  press  nj)on  the  tnhcrosity 
and  then  pass  the  linger  along  the  ridge  from  tiie  tuberosity  toward  the 
front,  and  observe  whether,  on  pressure  at  any  point,  the  plate  is  dis- 
placed or  not,  or  whether  it  is  pressed  down  at  any  point,  and  when  the 
pressure  is  released,  it  springs  back  again.  This  is  termed  a  "spring," 
and  whether  a  serious  defect  or  not  depends  upon  its  location  and  ex- 
tent. Then  change  the  position  of  the  fingers,  and  press  upon,  say, 
the  most  prominent  point  of  the  right  tuberosity  immediately  over  the 
ridge  and  on  the  left  side,  about  the  location  of  the  canine  tooth.  Do 
this  for  each  side.  Then  press  upon  each  tuberosity;  we  are  apt  to 
find  a  spring  here,  owing  to  the  plate  being  "drawn  in;"  this  may  be 
remedied  by  slightly  "springing"  it  out;  that  is,  ])y  spreading  the  back 
part  of  the  plate,  ])eing  careful,  however,  that  while  correcting  this  de- 
fect, we  do  not  cause  another  at  some  other  point.  While  it  is  not 
essential  that  these  manipulations  should  be  followed  in  the  order 
here  given,  there  is  a  great  advantage  in  always  following  the  same 
order,  and  systematically  going  over  a  plate  and  determining  where 
it  does  and  where  it  does  not  fit,  before  any  attempt  at  correction  is 
made. 

The  defects  here  referred  to  are  those  apt  to  l)e  found  in  a  properly 
swaged  plate,  and  are  due  to  the  mechanical  difficulties  encountered  in 
changing  a  flat  piece  of  sheet  metal  to  the  complicated  form  of  a  dental 
plate,  rather  than  to  imperfections  in  the  tools  used.  Theoretically, 
if  the  plate  fits  the  die  perfectly,  it  should  fit  equally  well  the  model 
from  which  it  was  made,  provided  that  the  die  is  an  accurate  reproduc- 
tion of  the  model.  Practically,  no  die  is  absolutely  accurate,  nor  will  it 
retain  its  first  accuracy  under  the  stress  of  use,  nor  yet  is  it  possible  to 
swage  the  sheet  metal  with  absolute  accuracy  into  perfect  contact  with 
the  die.  Good  workmanship  ensures  a  close  approximation,  the  dex- 
terous use  of  expedients  and  tools  completes  the  task.  Reswaging  the 
plate,  with  the  die  corrected  at  the  point  in  fault,  is  often  eflfective  in 
relieving  a  rock;  at  times,  however,  while  correcting  one  fault  it  creates 
another.  If  the  misfit  is  serious,  it  is  better  to  make  a  new  die;  repeated 
swagings,  with  the  die  corrected,  first  at  one  jjoint  and  then  at  another, 
always  result  in  failure. 

A  spring  due  to  the  plate  binding  on  the  outside  of  the  ridge  may  be 
corrected  by  placing  a  few^  thicknesses  of  thin  ])ai)er,  dampened  so  as  to 
bend  to  the  model,  over  the  point  where  the  plate  binds,  and,  placing  the 
plate  in  position,  by  striking  it  a  few  blows  inside  the  ridge  with  the  face 
of  the  hammer.  A  little  practice,  much  more  certainly  than  extended 
explanation,  enables  an  observant  workman  to  quickly  determine 
whether  the  dies  are  in  fault  or  not,  and  the  best  means  of  locating 
and  correcting  remediable  defects  in  a  swaged  plate  after  the  dies  have 
done  all  that  they  can  do.  No  plate  should  receive  its  final  fitting  to 
the  model  until  after  it  has  been  well  annealed,  as  until  annealed  some 
portions  of  the  metal  are  under  tension.     If  fitted  before  annealing, 


MAKING   THE  PLATE.  567 

tlie  fit  is  iii)t  to  chan.ue  the  first  time  the  j)late  is  heated,  as  for  instance 
in  solderiiii^. 

After  the  plate  has  been  made  to  fit  the  model  satisfactorily,  the  edges 
should  receive  final  attention.  They  are  to  be  made  to  fit  closely  at  all 
points.  The  ri\eting  blade  of  the  bench-hammer,  or  a  pair  of  narrow- 
pointed  pliers  are  used  to  accomplish  this.  When  using  the  pliers,  do 
not  bend  in  the  extreme  edge  of  the  plate,  but  lightly  grasp  the  plate  in 
the  pliers  and  gently  bear  it  in  the  desired  direction.  The  centre  of  the 
back  edge  of  the  plate  should  not  be  made  to  press  hard;  usually  this 
part  of  the  mouth  is  hard  and  unyielding,  while  on  either  side  it  is  just 

Fig.  536 


The  chamber-piece  held  in  position  for  soldering  by  two  iron  wire  clamps.  The  chamber-piece 
shown  extends  to  the  back  edge  of  the  plate. 

the  reverse.  It  is,  therefore,  better  to  allow  it  to  fit  rather  loosely.  If 
the  plate  has  a  soldered  chamber,  the  edges  of  the  opening  should  now 
be  made  to  fit  the  model  closely  all  around,  and  after  they  have  been 
made  rounding  and  smooth,  the  chamber  is  to  be  soldered  in  place. 
If  due  care  is  used  in  this  operation,  it  is  very  seldom  that  the  fit  is  at  all 
changed  in  soldering  the  chamber,  while  the  rigidity  it  gives  to  the  plate 
would  be  a  serious  handicap  if  it  was  soldered  in  place  before  the  plate 
was  fitted  to  the  cast.  While  it  is  not  impossible  to  swage  a  plate  after 
the  chamber  has  been  soldered,  to  do  so  usually  destroys  all  the  advan- 
tage gained  by  the  soldered  over  the  swaged  chamber,  because  of  the 
closer  fit  of  its  margins,  and  is  liable  to  crush  it  in  and  seriously  mar 
its  appearance. 

Attaching  the  Chamber-piece. — When  the  plate  fits  the  model  cor- 
rectly, the  chamber-piece  is  placed  in  position  and  it  is  noted  whether 
it  is  in  perfect  contact  with  the  plate.  This  is  usually  the  case  if  it  has 
been  once  swaged  with  the  plate,  and  its  position  is  quite  satisfactory. 
At  times,  however,  it  may  be  desirable  to  slightly  change  its  position, 
it  is  then  necessary  to  refit  its  margins  to  the  new  position,  at  least  for  a 
sufficient  distance  to  solder  a  portion  of  its  margin.  The  contact  sur- 
faces are  first  scraped  until  clean  and  bright.    Borax  is  applied  to  the 


568 


SWAGED  METALLIC  PLATES. 


prepared  surfaces,  and  the  cap  is  clamped  to  the  plate  by  means  of 
two  clamps  made  of  No.  16  iron  wire  as  shown  in  Fig.  536,  one  applied 
to  either  side  of  the  chamber-piece  flange,  or  by  a  single  piano  wire 
clamp  (F'igs.  537,  538)  made  to  press  on  the  under  side  of  the  plate  at 
three- points,  and  to  bend  over  the  back  of  the  plate  and  hold  the  piece 


Chamber-piece  held  in  place  for  soldering  by  piano  wire  clamp. 

in  place  by  pressure  upon  its  centre.  This  has  the  advantage  of  not  in- 
terfering with  the  soldering  operation,  is  easily  applied,  and  is  effective. 
Very  little  pressure  is  needed  to  hold  the  chamber-piece  in  place;  it  is 
well  to  remember  that  the  plate  becomes  (juite  pliable  at  the  temperature 
at  which  solder  flows, and  that  if  the  clamp  is  made  to  press  too  strongly, 

Fig.  538 


Showing   the  shape  of  that  jiorlion  of  the  piono  wire  clanijj  resting    against   fhe  under  surface 

of  the  plate. 


it  will  surely  bend  the  plate.  The  plate  is  now  placed  upon  the  solder- 
ing support,  a  bed  being  made  for  it  so  that  it  is  supported  at  all  points; 
if  this  is  neglected,  the  plate  is  apt  to  bend  by  its  own  weight.  Woolly 
asbestos  wet  with  water  is  very  convenient  for  this  purpose.  When 
(juite  wet  it  ia readily  molded  to  any  shape,  it  cpiickly  dries  and  keeps 
its  shape  even  when  immediately  heated  very  hot.     A  small  square  of 


3/.4A7.\T,'   THE  PLATE.  569 

solder  is  applied  at  any  convenient  point,  preferably  at  the  forward 
extremity  of  the  chamber-piece,  and  the  broad  flame  of  a  blow-pipe  is 
vapidly  passed  around,  beneath,  and  over  the  plate  until  it  is  heated 
to  a  cherry  red,  when  a  fine  flame  is  directed  against  the  plate  near  the 
solder  until  the  latter  begins  to  fuse,  when  the  flame  is  thrown  upon  the 
flange  of  the  chamber-piece  and  the  molten  solder  drawn  beneath  it. 
As  soon  as  this  first  piece  has  flowed  sufficiently  to  tack  the  chamber- 
piece  in  place,  observe  if  the  parts  are  in  perfect  contact  all  around.  If 
this  is  the  case  the  operation  may  be  completed,  the  clamp  being  removed 
if  in  the  way.  If  a  separation  has  taken  place  at  any  point,  a  mis- 
hap that  not  unfrequently  happens,  let  the  plate  cool,  remove  the  clamp, 
and  placing  the  plate  on  the  model,  with  a  burnisher  press  the  flange  into 
close  contact  with  the  plate,  again  using  the  clamp  if  necessary  to  hold 
the  parts  in  place,  and  complete  the  soldering.  Place  the  next  piece  of 
solder  at  a  point  distant  from  the  first,  so  that  in  fusing  this  second  piece, 
the  first  will  not  be  re-fused  and  a  risk  of  the  piece  changing  its  position 
incurred.  Small  squares  of  solder  are  added  as  may  be  needed  to  com- 
plete the  operation.  It  is  not  advisable  to  place  all  the  solder  needed 
in  position  at  once,  unless  the  operator  is  an  expert,  as  there  is  a  great 
risk  of  the  solder  running  where  it  is  not  wanted  unless  the  plate  is  very 
evenly  heated.  Placed  one  or  two  little  pieces  at  a  time,  the  solder  is 
much  more  under  control.  Especial  care  should  be  exercised  to  prevent 
the  solder  flowing  anywhere  else  but  under  the  margin  of  the  chamber. 
If  it  flows  over  the  margin,  or  on  the  side  of  the  chamber,  the  beauty  of 
the  work  is  seriously  marred,  as  it  cannot  wholly  be  removed;  cut  away 
and  polished  as  carefully  as  it  can  be,  it  leaves  a  mark  that  will  show. 
If  the  edges  of  the  margin  are  left  square,  and  are  intended  to  show  in 
the  finished  work,  it  is  best  to  cut  the  solder  in  narrow  strips,  say  about 
a  thirty-second  of  an  inch  wide  and  about  one-eighth  of  an  inch  long, 
and  to  so  direct  the  fine  flame  of  the  blowpipe  that  it  is  all  drawn  under 
the  margin,  leaving  the  edge  of  the  covering  piece  sharply  defined. 
^^^len  the  soldering  is  complete,  examine  and  make  sure  that  the  joint 
line  on  the  palatal  aspect  of  the  plate  is  %yell  filled. 

The  plate  is  now  boiled  in  the  acid  solution,  washed,  and  dried.  It 
is  now  tried  upon  the  model.  If  the  soldering  has  been  carefully  done, 
the  plate  T^^ill  have  suffered  no  change  in  form.  Every  effort  should  be 
made  that  this  may  be  the  case,  as  the  plate  cannot  be  reswaged  without 
seriously  impairing  the  usefulness  and  the  appearance  of  the  chamber. 
Unless  the  clamps  have  been  unduly  strong  or  improperly  placed,  or 
the  plate  carelessly  placed  on  the  soldering  support  or  over-heated,  no 
fitting  ^"ill  be  required  other  than  to  make  the  edges  of  the  plate  fit  more 
closely.  When  this  has  been  done,  the  edges  are  smoothed  and  rounded , 
first  T\-ith  a  very  fine  cut  file,  and  finished  with  No.  0  emery  or  sand 
paper;  the  surface  of  the  plate  is  then  cleaned  and  brightened,  either  by 
being  scoured  with  white  sand  used  with  the  fingers,  or  ■v\-ith  brush 
wheels  and  pumice  stone  at  the  polishing  lathe.  It  is  now  ready  for 
trial  in  the  mouth. 


570  SWAGED  METALLIC  PLATES. 

Partial  Upper  Plates. — Plates  for  partial  upper  dentures  arc  of  three 
varieties :  first,  those  retained  by  means  of  a  vacuum-chamber;  second, 
those  held  in  position  by  means  of  clasps  attached  to  the  natural  teeth; 
and  third,  those  in  which  these  two  forms  of  retention  are  combined. 
Fig.  534  illustrates  the  first  variety.  Great  care  and  judgment  are 
called  for  in  arranging  the  plate  line  of  partial  plates:  the  peculiari- 
ties of  such  cases  are  so  varied  that  it  is  impossible  to  give  any 
but  general  directions.  The  number  of  teeth  to  be  supported,  the 
character  and  position  of  the  remaining  natural  teeth  and  of  the  an- 
tagonizing teeth,  are  important  factors  to  be  considered.  As  a  rule 
they  should  be  as  small  as  possible  and  yet  be  firmly  sustained;  at  times, 
however,  it  is  wise  to  extend  the  plate  beyond  the  recjuirements  of  im- 
mediate need  in  anticipation  of  further  tooth  loss.  In  arranging  the 
posterior  edge  of  the  plate,  advantage  may  be  taken  of  any  natural  de- 
pressions in  the  roof  of  the  mouth  in  which  the  edge  of  the  plate  may 
rest  and  be  less  in  the  way  of  the  tongue.  A  plate  supporting  any  teeth 
anterior  to  the  molars  may  end  at  the  interspace  between  the  second 
bicuspid  and  the  first  molar  or  the  middle  of  the  first  molar  of  each  side. 
It  is  better  to  well  round  the  corners,  forming  the  outline  of  the  posterior 
edge  in  graceful  curves,  as  shown  by  Fig.  534,  and  avoid  the  triangular 
points,  which,  while  adding  nothing  to  the  usefulness  of  the  plate,  are  so 
easily  bent.  Avoid  rigidly  all  fanciful  forms;  they  are  entirely  out  of 
place. 

Partial  vacuum-chamber  plates  are  usually  much  more  cumbersome 
than  are  clasped  plates,  and  as  a  rule  are  not  as  firmly  held  in  place. 
They  are  used  in  cases  where  it  is  desirable  to  avoid  all  risk  of  injury  to 
the  remaining  natural  teeth,  or  where  the  remaining  teeth,  from  their 
position,  shape,  or  condition  interdict  the  use  of  clasps.  The  method 
of  their  construction  differs  in  no  wise  from  that  of  clasped  plates,  ex- 
cept as  regards  the  vacuum-chamber,  which  may  be  swaged  with  the 
plate,  or  soldered;  in  either  case  the  manipulations  are  precisely  the 
same  as  those  required  in  constructing  the  vacuum-chamber  of  a  full 
plate. 

Partial  plates  supported  by  clasps  are  usually  made  narrow;  fre- 
quently the  posterior  line  may  be  drawn  almost  entirely  in  the  depression 
of  the  rugse,  thus  placing  it  where  it  is  least  in  the  way  of  the  tongue. 
They  are  often  made  too  small.  It  must  be  remembered  that  unless 
there  is  sufficient  bearing  surface  the  pressure  of  mastication  will  press 
them  painfully  into  the  roof  of  the  mouth.  And  again,  an  effort  is  made 
to  retain  plates  with  but  slight  attachment  to  the  natural  teeth,  under 
the  impression  that  the  teeth  are  thus  saved  from  injury.  This  is 
often  a  mistake;  an  extra  clasp  will  often  hold  a  plate  more  firmly,  and 
while  making  it  more  comfortable  for  the  patient,  will  lessen  the 
strain  and  wear  upon  the  teeth  to  which  it  is  attached.  When 
the  plate  extends  from  one  side  of  the  mouth  to  the  other,  and  is 
made  narrow,  some  dental  mechanics  prefer  to  make  two  thin  plates 
and  solder  them  together  in  order  to  make  the  plate  more  rigid  and  less 
liable  to  bend.     Others  prefer  to  make  the  plate  heavier  and  secure 


MAKISG   THE  PLATE.  ,571 

rigidity  by  addiiifj  reiiiforciiiji  pieces  where  needed  at  the  time  the 
teeth  are  soldered.  A  strong  serviceable  ])hite  can  be  made  in  either 
wa\'. 

The  first  step  in  constrncting  a  partial  plate  is  to  mark  the  plate  out- 
line upon  the  model.  First  consider  the  position  and  number  of  teeth 
the  plate  is  to  support,  and  the  probable  number  and  position  of  those 
which  it  may  be  required  to  support  in  the  near  future.  If  a  vacuum- 
chamber  plate,  the  next  consideration  is  the  posterior  plate  line.  This 
should  be  located  to  make  the  plate  as  small  as  may  be  consistent  with 
firm  retention,  and  in  all  cases  must  be  kept  well  within  the  limits  of 
the  hard  palate.  Fig.  534  is  suggestive  of  the  form  this  should  take. 
If  supplemental  clasps  are  to  be  added,  the  plate  must  be  extended  to  in- 
clude the  teeth  upon  which  they  are  to  be  adjusted.  The  anterior  line 
of  the  plate  follows  closely,  in  both  clasped  and  vacuum-chamber  plates, 

Fig.  539 


Partial  clasped  plate  supporting  the  anterior  teeth;  showing  a  backward  extension  ol 
of  the  plate  to  overcome  a  tendency  to  drop  in  front,  and  to  relieve  the  supporting  teeth 
of  a  strain  they  would  otherwise  sustain. 

the  lingual  borders  of  the  remaining  natural  teeth,  and  should  extend 
through  the  vacant  interspaces  to  the  edge  of  the  ridge  if  plain  teeth  are 
used,  and  over  it  as  would  be  the  case  of  a  full  plate  if  gum  teeth  are  re- 
quired. It  is  desirable  when  making  the  plate,  to  let  the  plate  extend 
quite  as  far  at  this  point  as  will  be  needed,  and  to  reduce  its  size  as  may 
be  necessary  when  fitting  the  teeth  in  place.  In  marking  the  plate 
outline  of  a  clasped  plate,  the  teeth  to  be  supplied,  and  also  the  teeth 
selected  to  sustain  it,  are  to  be  considered.  The  plate  should  be  com- 
pact, as  small  as  is  consistent  with  comfortable  use,  and  of  a  form  favor- 
ing rigidity.  These  are,  however,  general  considerations  only.  As  a 
rule  the  posterior  line  should  not  include  more  than  the  last  vacant 
space  or  the  last  clasped  tooth ;  nevertheless,  in  some  cases,  as  for  instance 
Figs.  539  and  540,  where  the  clasped  teeth  are  quite  short  or  so  shaped 
that  the  clasps  upon  them  do  not  hold  firmly,  a  backward  extension  of 
the  plate  may  cause  it  to  be  more  firmly  held;  in  that  case  especial  care 


572  SWAGED  METALLIC  PLATES. 

Is  needed  to  so  strengtlien  these  portions  of  the  plate  that  they  be  not 
readily  bent  out  of  shape. 

Fig.  540 


A  partial  clasped  jilate  sustained  mainly  by  a  short,  or  unfavorable  shaped  bicuspid  tooth  on 
eadi  side.  In  such  cases,  the  plate  may  be  held  more  firmly  by  a  supplemental  clasp  on  a  front 
tooth,  a  backward  e.xtension  of  the  plate,  A.  A.,  or  a  collar  clasp  on  one  or  more  molar  teeth,  as 
shown. 

The  manipulations  of  swaging  a  partial  upper  plate  follow  closely 
those  of  swaging  a  full  upper  plate.     'J'he  least  desirable  die  is  selected 


A  partial  clasped  jjlate  confined  to  one  side  of  the  mouth,  sustained  mainly  b>-  a  molar  tooth. 
A  supplemental  clasp  on  the  canine  tooth  ensures  greater  firmness,  and  relieves  the  molar  of  a 
strain  it  would  otherwise  sustain.  A  supplemental  clasp  may  be  adjusted  to  any  tooth  deemed 
best,  or  most  available. 

from  which  the  teeth  are  removed  by  means  of  a  cold  chisel  or  a  hack- 
saw, supplemented  by  a  coar.se  flat  file  until  nothing  more  than  an  out- 


MAKING  THE  PLATE. 


573 


An  unsatisfactory  form  of  clasped  plate  supporting  an  anterior  tooth  and  sustained  by  a  ciasp 
on  a  molar  tooth.  Owing  to  the  leverage  upon  the  clasp,  not  only  is  the  plate  liable  to  displace- 
ment, but  in  addition  the  strain  upon  the  sustaining  tooth  is  excessive.  In  such  cases  it  is  more 
satisfactory  to  make  the  plate  as  shown  by  the  dotted  line,  clasping  a  bicuspid  tooth  on  each 
side. 


Fig.  543 


line  remains.  Sufficient  should  be  removed  that  the  plate  may  be 
swaged  over  them  without  being  torn,  and 
yet  enough  left  to  plainly  mark  their  posi- 
tion on  the  plate,  as  a  guide  when  fitting 
it  to  the  cast.  To  prevent  the  plate  sliding 
backward  it  is  occasionally  desirable  to  let 
the  tooth  immediately  posterior  to  the 
plate  line  remain,  and  to  make  in  it  a  saw- 
cut  to  receive  the  back  edge  of  the  plate. 
This  sliding  backward  of  the  plate  during 
the  swaging  process  must  be  guarded 
against  at  all  stages  of  making  a  partial  up- 
per plate,  especially  those  embracing  only 
the  anterior  portion  of  the  cast.  They  do 
not,  as  a  rule  extend  over  the  alveolar  ridge, 
nor  yet  are  they  supported  by  the  flat  por- 
tion of  the  palatal  vault.  Resting  as  they  do 
upon  a  sharply  inclined  surface,  their  natu- 
ral tendency  is  to  slide  backward  as  the  die 
is  forced  into  the  counter-die.  In  making 
a  plate  such  as  Fig.  540,  it  may  be  treated, 
in  all  essential  particulars  as  though  it  was 
a  full  upper  plate,  the  only  difference,  in-  ,  L°wer  piate-bending  pliers,  used  to 

,  T  •  1        i>    n      1  1     •  1        bend  a  lower  plate  into   a   gutter-like 

deed,  between  it   and   a  tuU   plate  bemg  the   form  preparatory  to  swaging.     They 
extent   of   surface   it   covers.      In   making  a   ^re  also   used  to  give  a  concave  form 

smaller  plate,  such  as  Figs.  541  or  542,  the  r^Xi, ^Zr tS".:'"'' '°  " 


r,Tl  ^\vA(;i':u  metallkj  i'i.ates. 

cliicf  (liffifulty  encountered  is  usually  to  hold  it  in  j)lace  until  suffic- 
iently swaged  as  to  become  fairly  well  fixed  in  position  upon  the  die. 
This  may  be  facilitated  by  sharply  beiuKno;  the  edge  with  a  pair  of  flat 
pliers  so  that  it  rests  upon  the  portion  of  the  die  representing  the  ridge, 
or  in  some  cases,  first  fitting  it  into  the  counter  die.  Now  and  again 
it  may  l)e  more  securely  held  by  raising  u})on  the  counter  the  with  a 
graver  one  or  more  strong  burs,  just  at  the  edge  of  the  plate,  bending 
them  over  the  plate  so  as  to  hold  it  in  position  during  swaging.  A 
small  narrow  plate  is  less  manageable  with  the  mallet  when  fitting  it 
to  the  die  prelimiiuiry  to  swaging,  and  is  liable  to  displacement  during 
the  early  stages  of  this  operation.  When  the  plate  is  well  swaged,  on 
the  first  die,  it  should  be  roughly  shaped  to  the  plate  lines,  and  then 
finally  swaged  upon  the  second  die.  Unless  it  is  by  its  form  securely 
held  in  position,  this  must  be  carefully  done  to  avoid  swaging  it  to  a 
new  position  and  thus  spoiling  the  plate.  In  all  cases  until  the  final 
swaging  is  complete  the  plate  should  be  allowed  to  extend  slightly  over 
the  anterior  line,  as  with  all  possible  care  there  is  a  slight  movement 
from  it.  The  suggestions  as  to  frequent  annealing,  and  the  precaut- 
ions to  be  ol)served  to  avoid  contamination  with  base  metals  apply 
with  equal  force  to  all  swaging  operations.  Small  plates,  and  partial 
plates  simple  in  form,  may  be  constructed  upon  one  die;  there  is,  in 
such  cases,  less  for  the  die  to  do. 

After  the  swaging  is  complete  and  the  plate  fits  the  model  satisfacto- 
rily it  is  then  carefully  shaped  to  the  plate  lines,  especially  those  along  the 
lingual  aspect  of  the  remaining  natural  teeth.  As  a  rule,  the  plate 
should  fit  their  margins  accurately.  In  exceptional  cases  the  anterior 
plate  line  may  be  located  w^ell  within  the  line  of  the  teeth,  as  for  instance 
to  avoid  interference  with  opposing,  teeth,  etc.;  some  operators  prefer 
that  it  should  do  this  in  all  cases,  holding  that  cleanliness  and  comfort 
are  promoted  thereby.  The  plate  is  now  ready  for  soldering  in  the 
chamber,  or  to  be  fitted  with  clasps,  if  these  are  to  be  added,  after  which 
the  edges  are  smoothed,  its  surface  well  cleansed  and  prepared  for 
adjustment  to  the  mouth. 

Full  Lower  Plate. — Before  commencing  to  form  a  low^er  plate  upon 
the  dies,  when  the  ridge  is  sharp  and  prominent,  it  is  an  advantage  to 
give  it  a  gutter-like  form  by  use  of  the  lower-plate,  bending  pliers  Fig. 
54,3,  or  in  default  of  these  it  may  be  readily  done  with  the  blade  of  the 
bench  hammer,  the  plate  being  held  over  a  V-shaped  groove  formed  in 
the  end  of  a  piece  of,  hard  wood  held  in  the  bench  vise.  The  plate 
thus  prepared  can  be  fitted  to  the  dies  more  rapidly  and  with  less 
injury  to  the  metal  of  which  it  is  made  than  if  the  work  was  entirely 
done  upon  the  dies.  Where  the  ridge  is  wnde,  however,  it  is  better 
to  form  it  over  the  dies,  beginning  at  the  mesial  line  by  first  slightly 
bending  the  outer  edge  down  with  the  mallet,  and  then  fitting  the 
inner  portion,  and  so  progressively  on  each  side  toward  the  distal 
end  of  the  ridge.  When  the  plate  has  thus  been  made  to  conform  to 
the  die  suflHciently  well  to  retain  its  position  it  is  lightly  swaged  into 
the  counter-die.     As  in  making  an  upper  plate,  this  must  be  done  cau- 


MAKIXCr   THE  PLATE  575 

tioii-sly  and  any  mal-position  promptly  corrected.  If  the  sheet  metal 
form  is  correct  in  shape  but  little  difficulty  will  be  experienced.  If, 
however,  this  is  faulty,  the  tendency  to  bend  over  inside  the  ridge  if 
the  form  has  been  of  too  sharp  a  curve,  or  to  the  outside  if  it  has  not 
been  sufficiently  curved,  will  be  pronounced  and  difficult  to  overcome. 
If  the  error  is  not  excessive,  patience,  and  careful  manipulation  with 
the  fingers  and  the  mallet  may  correct  it.  If  the  plate  is  made  of  a 
single  thickness  of  metal,  the  swaging,  fitting,  and  testing  the  fit,  etc., 
differ  so  httle  from  that  of  an  upper  plate,  that  further  description  is 
unnecessary.  It  is  usual,  after  a  lower  plate  made  of  a  single  thickness 
of  metal  is  complete  and  has  been  tested  in  the  mouth  and  found  to  fit 
satisfactorily,  to  solder  a  half-round  wire  along  its  edges,  inside  and 
outside  if  the  denture  is  not  to  be  rimmed,  and  inside  and  around  the 
distal  ends  only  if  a  rim  is  desired.  The  object  of  this  is  not  only  to 
afford  additional  strength,  but  to  make  the  edge  thick  and  rounded  and 
less  liable  to  cut  into  the  soft  tissues.  The  wire  should  be  quite  light, 
say,  one-sixteenth  of  an  inch  wide  on  the  flat  side.  It  is  fitted  and  sol- 
dered to  the  plate  in  the  following  manner :  take  a  piece  of  half-round 
wire  sufficiently  long  for  the  work  in  hand,  and  beginning  at  a  point 
about  an  inch  from  the  left  distal  end  of  the  plate,  lay  the  flat  side  of  the 
wire  against  the  inside  edge  of  the  plate,  bending  it  with  the  pliers  so 
that  it  will  fit  accurately  along  the  edge  for  about  an  inch.  Do  not  begin 
at  the  end  of  the  wire,  but  leave  enough  to  well  go  round  the  distal  end 
and  hold  this  in  place  with  two  bands  of  binding  wire  (annealed  iron 
wire  of  about  24  guage).  The  binding  wire  is  passed  over  the  plate 
and  its  free  ends  twisted  together.  Make  the  edge  of  the  half-round 
wire  lie  exactly  on  the  edge  of  the  plate.  There  is  a  tendency  in  the 
binding  wire  to  draw  the  half-round  wire  too  far  in;  this  is  corrected 
after  it  has  been  made  tight,  by  placing  the  edge  of  one  blade  of  a  pair 
of  pliers  ou  the  binding  wire,  just  beyond  the  inner  edge  of  the  half- 
round  wire,  and  the  other  blade  at  the  edge  of  the  plate;  a  slight  pres- 
sure will  bend  in  the  binding  "W'ire  and  hold  the  half-round  wire  securely 
in  place.  The  binding  wire  should  not  be  twisted  too  tight,  or  it  will 
distort  the  plate.  By  twisting  it  just  enough  to  hold,  and  then  pressing 
that  portion  which  passes  under  the  plate  into  the  gutter  of  the  plate 
with  a  blunt  instrument,  it  will  be  drawn  sufficient  tight  without  risk 
of  bending  the  plate.  This  portion  of  half-round  wire  is  now  soldered; 
in  doing  this,  the  plate  must  be  carefully  supported  at  all  points  to 
prevent  its  changing  shape  during  the  operation,  and  the  blowpipe 
flame  carefully  directed  so  as  not  to  melt  the  free  portion  of  half-round 
wire.  A  skilful  workman  will  generallv  at  this  stag-e  fit  the  T^'ire  all 
around  and  complete  the  operation  in  one  additional  soldering;  this  is 
not  necessary,  how^ever;  if  found  more  convenient  to  fit  and  solder  an 
inch  or  two  at  a  time,  there  is  but  little  risk  of  warping  the  plate  by 
repeated  soldering  if  the  plate  is  well  supported.  In  applying  heat  do 
not  direct  the  flame  directly  on  the  wire  or  it  will  spring  away  from 
the  plate.  The  soldering  should  be  done  continuously  from  the  point 
at  which  it  is  commenced.      If  it  is  tacked  at  intervals  it  is  apt  to 


576  SWAGED  METALLIC  PLATES. 

spring  from  the  plate  when  the  intervening  spaces  are  soklered.  Do 
not  use  too  much  solder,  if  the  wire  is  neatly  fitted  to  the  plate  and 
held  in  position  with  binding  wire  at  short  intervals,  very  little  will  be 
needed.  Sufficient  heat  should  be  applied  to  make  it  flow  freely.  If 
the  case  is  to  be  rimmed  omit  the  wire  from  that  portion  the  rim  will 
occupy.  "Wiring"  a  lower  plate,  as  this  operation  is  called,  is  a  decided 
improvement,  and,  while  adding  very  much  to  its  appearance  and 
strength,  makes  it  more  comfortable  for  the  patient.  While  it  is  not 
impossible  to  res  wage  a  lower  plate  after  it  has  been  wired,  the  oper- 
ation is  complicated  by  the  presence  of  the  wire,  especially  if  the  alve- 
olar ridge  is  thin  and  sharp.  If  due  care  is  used  in  properly  supporting 
the  plate,  and  avoiding  excessive  heat,  it  is  seldom,  indeed,  that  there  is 
any  serious  change  in  the  fit,  no  more  than  can  readily  be  overcome 
without  recourse  to  the  dies. 

In  constructing  a  double  plate,  make  each  plate  separately   until 
both  are  swaged  to  fit  the  cast  accurately,  but  do  not  trim  them  quite 

Fig.  544 


Two  thin  lower  plates  held  together  with  iron  binding  wire  preparatory  to  soldering.  The 
underneath  plate,  as  shown,  extends  a  little  beyond  its  fellow  so  as  to  form  a  ledge  convenient  for 
placing  the  solder;  this  ledge  is  removed  when  the  plate  is  finished. 

to  the  plate  line,  letting  the  one  that  is  to  be  underneath  extend 
a  little  beyond  the  other  so  as  to  form  a  ledge  upon  which  to  place  the 
solder.  After  annealing,  thoroughly  cleanse  the  surfaces  that  are  to  be 
in  contact  and  coat  them  with  borax  ground  to  the  consistency  of 
cream,  very  smooth,  and  free  from  any  gritty  particles.  Then  place  them 
between  the  dies  in  the  relation  to  each  other  they  are  to  occupy  when 
soldered,  placing  a  thickness  of  paper  on  each  side  so  that  they  will 
not  come  in  contact  with  the  dies,  and  swage  the  two  together.  The 
paper  is  used  to  avoid  the  necessity  of  "pickling"  them  before  solder- 
ing. Usually  when  swaged  together  they  are  brought  so  closely  in 
contact  that,  if  carefully  handled,  they  hold  together  with  sufficient 


MAKING  THE  PLATE.  577 

firmness  to  be  laid  upon  the  solder  support  and  soldered  without 
separating.  It  is  desirable  that  they  should  do  so;  if  they  do  not,  hold 
them  together  with  binding  wire  at,  say,  three  or  four  points  as  shown 
by  Fig.  544.  In  using  binding  wire  for  this  and  similar  purposes,  it  is 
well  to  remelnber  that  twisting  the  ends  together  practically  has  the 
tightening  effect  of  a  screw;  without  apparently  using  much  force 
it  is  quite  possible  to  draw  the  edges  of  the  plate  together  and  seri- 
ously impair  the  fit.  To  avoid  this,  twist  the  ends  of  the  wire  barely 
tight  enough,  and  further  tighten  the  wire  so  as  to  hold  the  plates 
firmly  together  by  slightly  bending  the  wire  that  passes  across 
the  edges,  either  by  pressing  it  in  with  a  blunt  instrument,  or  slightly 
by  twisting  it  sideways  with  a  pair  of  pliers.  It  is  by  these  means 
made  sufficiently  tight  without  being  so  rigid  as  to  bend  the  plate.  Al- 
ways make  it  a  rule  to  twist  the  ends  of  the  binding  wire  in  one  direction : 
while  it  is  in  all  cases  a  matter  of  choice,  the  habit  once  formed  of  doing 
it  in  a  certain  way  will  avoid  the  annoyance  of  disturbing  the  wire, 
by  twisting  it  in  the  wrong  direction  when  making  the  final  adjustment 
before  soldering.  Usually  one  wire  in  front,  and  one  on  each  side 
near  the  distal  ends,  are  all  that  are  required;  if,  however,  there  is  a 
tendency  in  the  plates  to  spring  apart  at  any  point,  an  extra 
wire  or  two  may  be  used  to  restrain  them.  After  adding  a  little 
fresh  borax  at  the  edges,  the  plates  are  adjusted  to  place  on 
the  soldering  support,  carefully  supported  at  all  points  so  that 
they  shall  not  bend  with  their  own  weight  when  heated,  and  a 
few  narrow  pieces  of  solder  of  the  same  fineness  as  the  plate, 
placed  along  the  lingual  border  of  the  ledge  formed  by  the  lower  plate 
projecting  beyond  the  other.  No  solder  is  placed  upon  the  labial  and 
buccal  portions  of  this  ledge.  The  solder  is  to  be  drawn  through  frorn 
the  lingual  side,  so  as  to  give  assurance  of  a  perfect  union  of  the  plates 
throughout. 

The  blowpipe  flame  is  passed  above  it,  not  on  it,  until  efflorescence  of 
the  borax  ceases,  when  a  broad  flame  is  applied  to  the  plate  until  it  is 
heated  to  a  uniform  red,  when  the  fine  flame  is  directed  against  the 
solder  pieces,  fusing  them  one  by  one.  Other  pieces  are  added  until 
there  is  a  uniform  line  of  solder  along  the  lingual  edge.  Unless  one  is 
expert  with  the  blowpipe,  it  is  better  not  to  place  too  much  solder  in 
position  at  the  beginning,  as  should  the  plate  not  be  evenly  heated,  it 
would  tend  to  flow  to  one  point,  and  perhaps  over  instead  of  between 
the  plates.  By  adding  a  little  at  a  time,  it  is  much  more  manageable. 
A  larger  flame  is  now  thrown  upon  the  labial  and  buccal  aspects  of  the 
plate  until  these  portions  are  at  a  higher  temperature  than  the  lingual 
edge,  the  heat  is  cautiously  carried  forward  until  the  entire  mass  of 
solder  is  seen  to  flow  like  water  and  appear  at  the  labial  and  buccal  por- 
tions of  the  joint,  uniting  the  plates  perfectly.  This  thorough  union  of 
the  plates  is  very  important,  as  if  a  small  portion  remains  unsoldered 
the  plate  will  be  apt  to  rise  up  at  that  point  in  subsequent  solderings, 
forming  what  is  technically  known  as  a  "blister."  When  cold  the  bind- 
ing wires  are  removed  and  the  plate  boiled  in  the  acid  solution.  The 
37 


578 


SWAGED  METALLIC  PLATES. 


ledge  of  the  lower  plate  is  trimmed  away,  using  for  this  purpose  the 
plate  nippers,  or  the  points  of  a  very  sharp  pair  of  curved  shears,  com- 
pleting the  trimming  with  files  until  the  plate  outline  corresponds  with 
the  i)late  lines  on  the  model;  its  edges  are  then  rounded,  and  smoothed 
with  fine  sand-  or  emery-paper. 

The  plate  may  be  reswaged  after  soldering,  if  necessary,  but  if  made 
to  fit  accurately  before,  antl  carefully  handled  during  that  operation,  it 
is  seldom  that  there  is  any  material  change  in  the  fit.  It  is  a  serious 
mistake  to  depend  upon  subsequent  reswaging,  and  to  solder  the  plates 


Fig. 


A  partial  lower  plate  supporting  the  posterior  teeth,  a  natural  molar  tooth  on  each  side  remain- 
ing. It  it  desirable  in  some  cases,  in  order  to  hold  the  plate  more  firmly  in  position, or  to  relieve  the 
sums  of  the  pressure  of  mastication,  to  extend  the  plate  over  the  molar  tooth  of  one  or  both  sides, 
as  shown.     The  reinforcing  piece  extends  backward  to  the  dotted  line. 


together  before  they  fit  the  model  accurately.  After  the  plates  are 
soldered  together  they  become  quite  rigid,  and  while  a  slight  warping 
may  be  readily  corrected  by  the  dies,  it  is  very  difficult  to  effect  any 
material  change  in  their  shape.  A  carefully  swaged  double  plate 
should  require  comparatively  little  solder  to  thoroughly  unite  its  .sep- 
arate portions.  If  by  any  mischance  they  should  separate  during  the 
operation,  and  an  excessive  amount  of  solder  be  required,  it  will  be 
apt  to  make  trouble  when  soldering  the  teeth;  sometimes  by  running 
out  at  the  joint,  and  at  other  times  by  melting  its  way  through  the  plate. 
The  pos.sibility  of  this  enforces  the  importance  of  care  and  exactness  at 
each  stage  of  the  work. 

A  partial  lower  plate  is  not  as  a  rule  cut  away  to  conform  to  the  gum 
line  of  the  teeth  as  is  an  upper  plate,  but  is  allowed  to  pass  up  over 


MAKIXa  Till':  PLATE.  579 

them,  and  is  made  to  fit  closely  their  lingual  surfaces.  This  is  done 
partly  to  give  greater  strength  to  the  plate  by  increasing  its  width  at 
points  where  it  otherwise  would  be  quite  narrow,  and  partly  to  allow 
it  to  rest  on  or  against  the  teeth,  and  thus  assist  the  narrow  ridge  in 
bearing  the  pressure  of  mastication.  It  also  makes  a  more  comfortable 
plate,  as  the  edges  are  not  so  liable  to  press  into  the  gum,  nor  yet  are 
they  so  perceptible  to  the  tongue.  In  preparing  the  first  zinc  die,  the 
teeth  are  cut  off  a  little  above  the  plate  line,  with  a  sharp  downward 
'bevel  on  the  outside,  so  that  the  plate  will  hook  over  and  be  less  liable 
to  be  driven  down  during  swaging.  Teeth  standing  alone,  and  the  end 
Teeth  of  a  series  should  be  rounded  on  their  approximal  sides  so  as  not 
to  tear  or  split  the  plate.  Teeth  which  are  to  be  fitted  with  clasps,  or 
when  for  any  reason  the  plate  is  not  required  to  extend  over  them,  may 

Fig.   546 


Showing  the  first  used  metallic  die  for  a  plate  like  Fig.  445,  prepared  for  swaging.  The  molar 
teeth  maj"  be  cut  off  as  shown  on  the  right,  or  a  saw-cut  may  be  made  as  shown  on  the  left,  to  receive 
and  hold  the  plate  in  position  during  the  first  stage  of  swaging.  The  reinforcing  piece  extends  back- 
ward on  both  sides  to  the  dotted  line. 

be  cut  down  to  the  gum  line,  leaving  sufE.cient  only  to  mark  their  out- 
line upon  the  plate.  When  the  teeth  to  be  supplied  are  in  the  front, 
and  all  together,  as  in  Fig.  539,  the  manipulation  of  making  such  a 
plate  differs  but  little  from  that  of  making  a  full  lower  plate.  The 
backings  of  the  teeth  and  the  solder  used  to  secure  them  to  the  plate, 
together  with  a  heavy  piece  of  plate  extending  from  the  clasp  on  either 
side  to  the  backing  of  the  nearest  artificial  tooth,  added  when  the  teeth 
are  soldered,  gives  it  all  the  stiffness  needed. 

\^'Tien  the  front  teeth  are  in  and  the  back  teeth  of  either  side  are  to  be 
supplied,  as  shown  in  Figs.  528  and  545,  the  task  is  much  more  difficult. 
The  front  teeth  are  filed  from  the  first  die  nearly  but  not  quite  to  the 
plate  line  as  in  Fig.  546,  and  sloped  so  as  to  leave  a  sharp  edge,  over 
which  the  plate  is  bent  so  as  to  hold  it  in  place  during  swaging.  The 
molar  teeth  in  a  case  like  Fig.  545  are  cut  off,  so  as  to  leave  only  enough 


580  SWAGED  METALLIC  PLATES. 

of  tlie  teeth  to  make  a  slight  indentation  in  the  plate  to  serve  as  a  guide 
in  tiling  it  to  fit  around  tlieni.  In  some  cases  instead  of  cutting  off  the 
molar  teeth  it  is  better  to  make  saw  cuts  as  close  to  the  gum  as  possible, 
and  let  the  ends  of  the  plate  pass  into  them  when  fitting  it  to  the  die,  so 
as  to  assist  in  holding  it  in  place.  (Fig.  546.)  There  is  usually  some 
little  difhculty  in  commencing  a  plate  of  this  kind.  It  is  apt  to  slip 
back,  or  when  fitted  to  the  front  teeth  it  does  not  well  cover  the  ridge 
on  each  side.  This  difficulty  is  very  much  increased  if  the  pattern  by 
which  the  piece  of  plate  is  cut  is  faulty  or  has  not  been  accurately  copied. 
After  htting  it  to  the  die  with  the  mallet  sufficiently  to  permit  it  being 
placed  in  the  counter-die,  it  may  be  bent  and  securely  held  in  place  by 
means  of  burs  raised  from  the  lead,  and  lightly  swaged  so  as  to  fix  it 
in  position.  The  first  effort  should  be  to  get  the  front  part  of  the  plate 
in  proper  position;  this  accomplished  by  bending  and  holding  the  sides 
in  their  proper  place  in  the  counter-die,  the  difficulty  can  be  overcome  by 
light  swaging  and  frequent  annealing.  After  the  plate  has  been  swaged 
to  fully  conform  to  the  die,  it  is  very  difficult  to  make  any  change  in  its 
position.  In  swaging  partial  lower  plates  such  as  these  there  are  three 
points  that  recjuire  special  attention:  first,  the  tendency  in  the  plate 
to  slip  down  in  front,  which  is  continued,  unless  there  is  a  marked  offset 
at  the  lingual  gum  line,  from  the  first  to  the  last  swaging  of  the  plate.  It 
is  checked  by  making  the  plate  hook  over  the  front  part  of  the  die;  and 
this  portion  should  not  be  removed  until  the  plate  is  so  far  advanced 
as  to  be  ready  to  swage  upon  the  second  die.  The  plate  should  not  be 
filed  accurately  to  the  upper  front  plate  line  until  it  is  fully  fitted  to  the 
cast,  and  is  completely  finished  so  far  as  swaging  is  concerned.  If  the 
front  teeth  have  an  outward  lean,  and  there  is  but  little  offset  at  the 
junction  of  the  teeth  and  gums,  the  plate  will  work  down  in  spite  of  all 
care;  to  provide  for  this,  allow  it  to  extend  a  full  sixteenth  of  an  inch 
beyond  the  plate  line  at  this  point.  Second,  a  tendency  to  fold  over 
or  form  a  crease,  generally  about  the  position  of  the  canine  teeth. 
This  must  be  closely  watched  and  the  fold  hammered  out  as  soon  as 
seen  and  before  it  becomes  fixed.  Third,  the  plate  is  liable  to  split  at 
about  the  same  points,  and  also,  in  some  cases,  about  the  middle  of 
that  portion  of  the  plate  covering  the  outside  of  the  ridge  on  either  side. 
Frequent  annealing,  skilful  use  of  the  mallet,  and  cutting  away  the 
surplus  metal  at  these  points  as  soon  as  it  can  be  safely  done,  will  usually 
prevent  it.  If  the  split  is  noticed  in  time,  by  cutting  it  off,  if  there  is 
sufficient  margin,  or  where  this  cannot  be  done,  soldering  a  piece  of 
plate  over  it,  will  usually  arrest  its  progress. 

It  is  desirable  that  those  portions  of  the  plate  covering  the  lingual 
surfaces  of  the  natural  teeth  fit  closely  to  them  and  into  the  interspaces; 
it  is,  therefore,  important  that  the  dies  be  accurate  at  these  points.  Usu- 
ally the  portions  representing  the  interspaces  will  need  a  little  carving; 
this  is  not  so  necessary  for  the  first  die,  but  the  second  or  finishing  die 
should  be  made  as  accurate  as  possible.  To  secure  close  adaptation 
at  this  portion  of  the  plate,  proceed  as  follows:  after  the  plate  has  been 
swaged  as  much  as  is  considered  necessary  on  the  first  die,  and  has  been 


MAKIXG  THE  PLATE.  581 

well  annealed,  place  it  on  the  second  die  and  holding-  it  firmly  in  place, 
with  a  luininierorniallet  antl  a  hone  eliaser  sucli  as  is  used  inniakinga 
swaged  vaeuuni-eavity,  drive  the  plate  into  the  interspaces  and  the  fes- 
tooned outlines  of  the  gum  of  each  tooth.     If  the  interspaces  are  deep 
and  sharp,  strike  light  blows  going  over  it  a  number  of  times,  and   if 
need  be,  annealing  the  plate  during  the  operation  so  as  to  "coax"  it  into 
place.     The  edge  of  the  chaser  will  need  resharpening,  as  it  breaks 
down  rapitUy.     Be  careful  not  to  cut  through  the  plate,  an  accident 
that  will  occasionally  happen,  and  while  not  a  serious  mishap,  one  that 
should  be  avoided.     This  operation  usually  bends  the  plate  very  much 
out  of  shape,  and  sometimes  changes  the  position  of  that  portion  extend- 
ing toward  the  distal  end  of  the  plate.    On  this  account  the  plate  should 
be    only  approximately  trimmed  to   the  lines    until   it  is    completed 
and  the  plate  well  swaged  on  the  second   die.     After  the  plate  has 
been  thus  fitted  to  the  lingual  surfaces  of  the  teeth,  it  is  fitted  on  the 
second  die  and  lightly  swaged.     First,  see  that  it  has  not  materially 
changed  its  position,  that  the  front  portion  has  not  been  driven  down, 
and  that  the  posterior  portion  reaches  the  plate  line  on  both  sides  of 
the  ridge.     Any  mal -position  is  readily  remedied  at  this  stage,  by  read- 
justing the  plate  to  position  in  the  counter-die  and  holding  it  in  its 
proper  place  by  burs  raised  along  its  edge  while  it  is  again  swaged. 
Next,  examine  the  plate  on  the  model  to  see  that  it  fits  the  model  and 
die  alike.    It  may  be  that  at  some  points  the  die  may  have  "dragged" 
slightly,  which  will  be  shown  by  a  space  under  the  plate  at  that  point 
when  the  plate  is  placed  upon  the  model.    If  this  is  the  case,  carve  the 
die  so  that  the  plate  fits  both  alike;  this  can  be  done  very  accurately  by 
carving  the  die,  placing  the  plate  on  it,  and  with  a  hammer  making  the 
plate  fit  the  die  at  the  point  carved,  and  testing  it  on  the  model,  repeating 
this  until  they  are  both  alike.    The  points  needing  special  attention  are 
around  the  teeth  next  the  spaces  to  be  supplied,  the  interspaces,  and 
the  edges  of  the  plate.     When  this  has  been  done,  again  go  over  the 
front  portion  of  the  plate  to  make  it  fit  against  the  lingual  surfaces  of 
the  teeth  accurately,  using  a  steel  chaser  if  necessary,  holding  the  tool  so 
that  it  will  carry  the  plate  into  place,  and  not  simply  make  an  indenta- 
tion into  it  or  cut  it  through.    The  plate  is  now  thoroughly  swaged  on 
the  finishing  die,  and  made  to  fit  the  model  accurately.     It  is  then 
ready  for  the  reinforcing  piece.     In  some  cases  that  portion  of   the 
plate  extending  inside  the  teeth  is  very  narrow  and  so   nearly  flat 
that  three  thicknesses   of   plate  are  needed  to  impart  the  required 
stiffness.     In  other  cases  it  is  wide,  or  so  corrugated  that  two  thick- 
nesses  of    comparatively  thin   plate  are  quite  sufficient.      If  three 
thicknesses    are   deemed    necessary,    the    first     reinforcing    piece   is 
made  narrower  than  the  plate  lines,  and  to  extend  only  a  short  distance 
beyond  the  last  tooth  of  the  series  on  each  side.     After  being  swaged 
it  is  filed  to  shape,  and  its  edges  all  round  filed  to  a  feather  edge.     It  is 
then  adjusted  to  place  on  the  plate,  (both  it  and  the  plate  having  been 
made  clean  and  prepared  for  soldering),  held  by  a  clamp  or  TN^ith  bind- 
ing -vsire  as  may  be  most  convenient,  and  a  trifle  of  solder  fused  at  some 


682  SWAGED  METALLIC  PLATES. 

point  where  the  two  are  in  contact,  i)referal)ly  at  a  central  point,  with 
the  object  of  holding  them  together  so  that  they  can  be  swaged  together. 
After  this,  the  soldering  is  completed.  The  second  reinforcing  piece 
is  now  made.  This  should  be  larger,  fully  the  width  of  the  plate  lines 
as  far  as  the  natural  teeth  extend,  tapering  and  extending  beyond  the 
last  tooth  of  each  side  to  fully  half  an  inch,  as  shown  by  the  dotted  line. 
Figs.  545  and  540.  No  special  care  is  taken  to  make  this  fit  into  the  inter- 
spaces, but  as  soon  as  it  is  sufficiently  swaged  to  j)crmit  its  being  prop- 
erly shaped,  it  is  tacked  to  the  plate  with  a  small  portion  of  solder  and 
swaged  with  it.  The  denture  is  more  easily  kept  clean,  is  more  com- 
fortable to  the  tongue,  and  has  a  more  artistic  finish,  if  this  portion  of 
its  lingual  surface  is  smooth  and  even;  it  is  not  desirable,  therefore, 
that  the  front  portion  of  the  reinforcing  piece  should  be  swaged  into 
the  interspace  with  the  same  accuracy  as  was  the  plate.  It  is  worthy 
of  note  that  the  reinforcing  pieces  are  not  made  to  fit  the  model ;  they  are 
fitted  to  the  plate,  and  as  the  surface  of  the  plate  against  which  they  fit 
difl'ers  very  much  from  that  which  fits  against  the  model,  the  plate  should 
be  in  place  on  the  die,  and  be  considered  as  part  of  the  die,  when  the  re- 
inforcing pieces  are  swaged.  Before  attaching  the  reinforcing  piece  to 
the  plate,  the  upper  edge  of  the  tapering  ends  should  be  well  bevelled. 
The  plate  should  extend  slightly  beyond  the  plate  line  as  far  as  the  re- 
inforcing piece  extends,  so  as  to  provide  a  ledge  on  which  to  place  the 
solder;  otherwise,  the  solder  is  liable  to  flow  under  the  plate  instead  of 
between  it  and  the  added  piece.  If  the  two  have  been  tacked  together 
it  is  seldom  that  a  clamp  is  needed  when  the  final  soldering  is  done.  As 
in  soldering  a  double  plate,  every  care  and  effort  should  be  taken  to  make 
the  solder  flow  thoroughly,  and  to  unite  every  portion  of  the  two  surfaces 
in  contact  with  the  least  possible  amount  of  solder.  As  to  accomplish 
this  the  heat  must  be  quite  high,  it  is  important  to  thoroughly  support 
the  plate  to  prevent  its  warping,  especially  if  it  is  of  silver.  With  pro- 
per care,  it  is  seldom  that  the  fit  is  materially  altered.  After  the  re- 
inforcing piece  is  soldered,  and  the  plate  has  been  cleansed  from  the 
borax,  etc.,  it  is  ready  for  final  adjustment  to  plate  lines,  and  the  portion 
beyond  the  reinforcing  piece  is  bound  with  half-round  wire.  This 
done,  the  plate  is  fitted  to  the  model,  the  edges  neatly  rounded  and  made 
smooth  and  its  surfaces  thoroughly  cleansed,  when  it  is  ready  for  ad- 
(justment  to  the  mouth. 

CLASPS. 

The  metal  of  which  clasps  are  made  should  possess  stiffness  and 
elasticitv  in  a  marked  degree;  it  should  also  be  tough  and  free  from 
brittleness.  An  allov  of  gold  with  about  two  grains  of  platmum  to  the 
pennvweight  answers  the  purpose  exceedingly  well;  if  carefully  made 
of  pure  metals  it  is  tough,  stiff,  and,  even  when  well  annealed,  is  as 
elastic  as  a  piece  of  spring-tempered  steel.     In  practicai  use  clasps  are 


CLASPS. 


583 


Fig.  547 


Fig.  548 


A  properly  shaped 
clasp. 


subjected  to  considerable  strain;  in  addition  to  this,  from  their  posi- 
tion, they  are  constantly  liable  to  accidents  while  the  denture  is  being 
handled  and  cleansed  l)y  the  patient.  To  withstand  this  the  metal 
must  possess  tenacity.  To  test  its  tenacity,  grasp  a  corner  of  the  well 
annealed  metal  firmly  with  a  pair  of  flat  pliers  and  quickly  bend  it  to  a 
sharp  right-angle.  If  this  causes  the  least  sign  of  a  break,  the  metal 
should  be  rejected.  Other  alloys  than  that  of  platinum  and  gold  have 
been  suggested  and  used  for  silver  dentures  on  the  score  of  economy. 
While  they  have  answered  the  purpose,  none  possess  any  practical  ad- 
vantage over  the  more  generally  used  alloy 
of  gold  and  platinum,  while  the  slightly 
smaller  cost  is  overbalanced  by  the  difh- 
culty  of  profitably  utilizing  the  scraps  and 
filings.  Laboratory  practice  is  simplified 
by  making  an  eighteen  carat  gold  and 
platinum  alloy  the  standard  for  all  clasps 
used  on  soldered  dentures,  whether  of  gold 
or  silver.  The  alloy  is  used  for  clasps  in 
the  form  of  plate  of  about  No.  25  gauge 
— seldom  heavier  than  No.  22,  and  seldom 
lio'hter  than  No.  27 — and  in  the  form  of 

CI 

half-round  wire.  Half-round  wire  is  used 
when  the  teeth  are  short,  so  as  to  obtain 
strength  with  a  narrow  clasp,  and  when 
the  clasp  passes  around  the  tooth  in  an 
irregular  line  to  avoid  pressing  upon  the 
gum,  or  to  obtain  a  firmer  hold  upon  the 
tooth.  The  peculiar  shape  of  half-round  wire  permits  its  being  bent  in 
any  direction,  and  on  this  account  it  can  be  more  readily  fitted  to  short 
molar  teeth,  and  a  clasp  made  of  it  will  often  grasp  them  far  more 
firmly  than  would  one  made  of  plate.  The  thickness  either  plate  or 
wire  should  possess  depends  entirely  upon  the  work  required  of  them 
and  the  position  they  occupy.  It  should  never  be  made  so  hea\7 
as  to  be  practically  Vigid :  the  free  or  unsoldered  porton  of  a  clasp 
should  be  elastic,  not  only  to  firmly  grasp  the  teeth,  but  also  to  slightly 
A-ield  under  severe  strain,  and  thus  ease  the  strain  upon  the  tooth 
to  which  it  is  adjusted. 

The  strongest  portion  of  all  clasps  should  be  where  they  are  united 
to  the  plate,  and  from  this  point  they  should  taper  to  the  free  ends. 
It  is  a  common  and  a  serious  fault  in  making  clasps  to  file  from  the  under 
edges  where  they  pass  around  the  appromixal  surfaces  of  the  teeth,  so 
as  to  keep  thena  from  pressing  unduly  upon  the  gums,  without  at  the 
same  time  so  shaping  the  upper  edge  that  the  clasp  shall  be  oi  uniform 
strength.  The  effects  of  this  is  to  make  a  weak  spot  at  a  point  where 
the  clasp  should  be  the  strongest;  all  the  bending  takes  place  at  this 
weak  point,  not  only  impairing  its  value  as  a  clasp,  but  invariably 
causing  it  to  break. '  If  after  properly  shaping  the  lower  edge  the 
clasp  is  reduced  in  width  toward  the  free  end  so  that  the  hollowed  out 


A  clasp  improperly 
shaped.  Having 
its  plate  edge  filed 
away  to  fit  the  gum 
makes  this  por- 
tion the  weakest 
point ,  impairing  its 
usefulness  b  y  d  e- 
stroying  its  elasti- 
city, andmaking  it 
liable   to  fracture. 


584  SWA  a  ED   METALLIC  PLATES. 

portion  ceases  to  be  the  narrowest  part  of  the  clasp,  its  strenfi:th,  useful- 
ness, and  (hiral)ility  will  he  very  nuich  increased.  A  properly  shai)ed 
clasp,  opened  out,  would  approximately  resemble  Fig.  547;  one  with 
the  defect  referred  to  is  represented  in  Fig.  548.  In  each  case  the 
attachment  to  the  plate  extends  from  a  to  b. 

If  it  is  necessary  that  the  clasp  be  narrower  near  the  plate  than  at 
the  free  end,  as  is  sometimes  the  case,  the  narrow  part  should  be  nuide 
correspontlingly  thicker — not  by  soldering  an  extra  piece  upon  it,  but 
by  making  it  of  thicker  plate,  and  filing  the  wider  portion  thinner,  so 
that  in  proportion  to  the  strain  upon  it,  it  will  be  of  uniform  strength 
throughout,  and  as  free  to  bend  at  one  part  as  another.  Before  begin- 
ning to  make  a  clasp  carefully  examine  the  shape  of  the  tooth,  its  posi- 
tion in  the  mouth,  and  its  relation  to  the  plate,  so  as  to  form  an  idea  of 
the  direction  and  amount  of  strain  it  will  be  required  to  resist,  and  from 
this  regulate  its  size,  shape,  position,  and  strength. 

In  making  clasps,  fit  them  to  the  teeth  before  soldering  only  so  far  as 
is  necessary  to  adjust  them  to  their  proper  position — usually  only  the 
palatal  and  approximal  surfaces,  anterior  and  posterior — leaving  that 
portion  which  is  intended  to  pass  around  the  buccal  or  labial  surfaces 
straight.  The  object  of  this  is,  first,  that  they  may  not  bind  upon  the 
teeth  so  tightly  as  to  prevent  their  being  readily  removed  from  the  model 
without  change  when  cemented  to  the  plate  prior  to  investing  for  sol- 
dering; and  second,  for  the  reason  that  in  many  cases  they  are  more 
securely  held  by  the  investment  when  so  made.  The  remaining  por- 
tion of  the  clasp  may  be  fitted  approximately  either  to  the  model,  or 
when  the  plate  is  adjusted  to  the  mouth,  but  only  so  far  as  to  lightly 
retain  it  in  place,  the  final  fitting  being  left  until  the  case  is  entirely 
finished.  If  prior  to  this  they  are  fitted  so  as  to  hold  the  plate  firmly, 
it  gives  a  great  deal  of  extra  trouble  in  adjusting  the  teeth,  without 
any  corresponding  advantage. 

In  making  clasps  the  following  tools  are  needed:  a  pair  of  strong,  but 
not  too  massive  round  nose-pliers  and  a  pair  of  narrow-beaked  flat 
pliers,  with  the  inner  edges  of  both  blades  rounded  so  as  to  remove 
the  sharp  square  edge.  These  are  essential.  A  tool  known  as  a 
clasp  bender  is  frequently  useful,  as  is  also  the  lower  plate-bender, 
(Fig  543),  the  former  is  used  to  concave  the  clasp  along  its  length  to  fit 
a  markedly  rounded  surface,  such  as  is  occasionally  found  on  molar  and 
bicuspid  teeth.  If  this  tool  is  not  at  hand,  the  same  effect  may  be 
produced  with  the  riveting  blade  of  the  bench  hammer. 

In  making  clasps  for  very  difficult  cases  it  is  occasionally  necessary 
after  fitting  them  with  the  pliers,  to  swage  them  between  dies:  this  is 
required  when  the  surfaces  to  be  fitted  are  rounded  or  the  shape  of  the 
tooth  very  irregular. 

It  is  not  usually  necessary  to  make  a  pattern  by  which  to  the  cut  the 
clasp  material  to  shape.  It  is  better  to  prepare  a  strip  of  plate  a  little 
wider  than  the  finished  clasp  is  intended  to  be,  so  as  to  allow  for  filing  the 
edge  to  fit  the  gum  at  the  neck  of  the  tooth,  and  long  enough  for  several 
clasps;  in  fact  a  little  longer,  as  it  is  quite  diflficult  in  practice,  without 


CLASPS.  585 

unduly  wasting  time,  to  make  the  first  bend  precisely  in  the  right 
place;  it  is  always  best,  therefore,  to  have  a  little  margin  for  possible 
errors.  Having  the  strip  long  makes  it  very  much  easier  to  handle. 
In  case  the  lingual  surface  of  the  teeth  are  markedly  bulging,  as  is 
frequently  the  case  with  upper  bicuspids  and  molars,  a  more  accur- 
ately fitting  and  more  effective  clasp  may  be  by  first  curving  the  strip 
making  the  side  that  fits  against  the  tooth  concave,  so  that  it  will  fit 
over  the  bulging  portion  of  the  tooth.  This  may  be  done  with  the  blade 
'  of  the  bench  hammer,  resting  the  strip  upon  a  lead  counter-die  or  on  the 
anvil,  but  more  conveniently  by  the  lower  plate-bender  represented 
in  Fig.  543. 

In  fitting  a  clasp  to  the  molar  tooth,  such  as  that  seen  in  Fig.  547,  lay 
the  strip  flat  against  the  anterior  approximal  surface  of  the  tooth,  allow- 
ing one  end  to  project  beyond  the  buccal  surface  as  far  as  it  is  intended 
to  pass  around  that  corner  of  the  tooth,  and  mark  with  a  pencil  or 
point  or  note  with  the  eye  the  position  of  the  first  bend  to  be  made  in  fit- 
ting the  clasp  to  the  palatal  surface,  and  with  the  round  or  narrow- 
beaked  pliers  or  clasp-benders,  as  may  be  preferred,  bend  it,  but  at 
first  not  quite  as  far  as  necessary,  so  as  to  be  able  to  correct  any  error 
made  in  the  first  bending  without  unduly  straining  the  metal  by  bend- 
ing it  back  again. 

The  clasp  is  now  placed  as  nearly  in  position  on  the  cast  as  its  shape 
will  permit.  Note  where  it  should  be  bent,  so  as  to  pass  around  the 
posterior  approximal  surface,  and  cautiously  bend  it  into  the  required 
shape.  Usually  it  will  be  necessary  to  file  the  lower  edge  of  the  clasp 
at  certain  points  to  allow  it  to  fit  well  down  to  the  gum  at  the  neck  of  the 
tooth,  especially  at  the  palatal  side;  it  is  desirable  to  do  this  before  the 
clasp  is  accurately  fitted  to  the  tooth,  as  it  may  somewhat  change  its 
position. 

This  may  now^  be  done,  at  least  so  far  as  to  allow  the  clasp  to  fit 
well  down  to  the  neck  of  the  tooth,  as  it  should  do  in  the  case  we  are 
now  considering.  In  many  cases  the  neck  fit  of  the  clasp  is  most 
important;  fitting  well  down  to  the  gum-line  and  close  to  the  tooth, 
enables  it  to  sustain  a  plate  firmly  and  comfortably,  wdthout  that 
strain  upon  the  tooth  inevitable  when  the  security  of  the  plate  depends 
upon  the  clasp  firmly  grasping  the  tooth.  The  clasp  fitting  under  the 
bulging  portion  of  the  tooth  holdsby  interlocking  with  the  body  of  the 
tooth,  w^hile  it  is  free  to  yield  to  slight  movements  of  the  plate  inci- 
dent to  its  proper  use. 

^Yhen  a  tooth  stands  alone,  as  represented  in  Fig.  539,  it  is  a  matter 
of  but  little  moment  on  w" hich  side  of  the  tooth  we  first  make  the  clasp  fit 
accurately;  but  when  it  passes  between  the  teeth,  after  the  clasp  is 
roughly  fitted,  make  the  portion  betw'eenthe  teeth  as  accurate  as  possi- 
ble, and  proceed  to  readjust  the  clasp  from  this  point  until  it  fits  the 
tooth  satisfactorily,  as  far  round  as  it  is  necessary  that  it  should  before 
soldering  it  to  the  plate. 

Invariably  begin  to  make  the  clasp  at  its  shortest  end;  when  this  end 
terminates  between  two  teeth,  but  does  not  pass  between  them,  make  it 


586  SWAGED  METALLIC  PLATES. 

pass  into  the  interspace  as  far  as  possible;  it  gives  the  clasp  a  much 
firmer  hold  iipcm  the  tooth. 

As  a  rule,  clasps  for  lower  teeth  are  not  fitted  close  to  the  gum  line :  the 
teeth  are  usually  longer  and  more  wedge-shaped  than  are  the  upper 
teeth.  To  hold  firmly  the  clasp  must  embrace  the  tooth  nearer  the  cut- 
ting edge:  this  is  made  necessary  by  the  fact  that  the  neck  is  so  much 
smaller  than  the  crown.  It  is  frequently  necessary  to  make  little 
hooks  or  lugs  to  catch  over  the  grinding  surface  of  lower  bicuspids  and 
molars  in  connection  w^ith  the  clasps  to  prevent  the  plates  pressing  too 
hard  upon  the  gums.  These  may  either  be  made  with  the  file — which, 
when  it  can  be  done,  is  the  best  plan — or  they  may  be  soldered  on  after 
the  clasp  has  been  soldered  to  the  plate  and  fitted  to  the  mouth.  It  is 
always  desirable  to  avoid  using  solder  for  any  purpose  on  that  part  of  a 
clasp  which  is  Intended  to  act  as  a  spring,  as  it  impairs  its  elasticity  by 
making  it  rigid  at  that  point.  When  clasps  are  applied  to  partial  low^er 
plates  carrving  posterior  teeth  only,  especial  care  is  needed  in  their  con- 
struction to  conteract  the  natural  tendency  in  such  plates  to  slide  back- 
ward. In  clasping  upper  teeth  that  are  markedly  wedge-shaped,  as  for 
instance,  the  canines,  and  all  teeth  where  the  gum  has  receded  and 
exposed  the  neck,  the  clasp  should  be  made  to  fit  the  tooth  at  its  largest 
part;  the  importance  of  this  is  self-evident.  In  some  cases  it  is  desir- 
able to  have  the  clasps  as  far  above  the  line  of  the  plate  that  it  is  neces- 
sary to  connect  them  by  a  narrow  strip  of  plate,  forming  what  is  known 
as  a  "standard  clasp."  Occasionally,  especialh  for  lower  plates,  when 
the  axes  of  the  clasped  teeth  are  at  such  an  angle  as  to  interfere  with  the 
adjustment  of  the  plate  and  clasps,  the  difficulty  may  be  overcome  by 
making  the  standards  elastic,  by  making  them  of  half-round  platinous 
gold  wire-  Standard  clasps  are  not  as  a  rule  desirable.  They  are  not 
as  cleanly  as  is  a  clasp  soldered  directly  to  the  plate,  and  are  more  liable 
to  accident. 

Stay  or  collar  clasps,  are  useful  appliances  to  assist  in  supporting 
partial  vacuum-chamber  plates,  to  assist  in  supporting  clasped  plates,  or 
where  a  clasp  is  needed  and  no  space  exists  through  which  a  clasp  may 
be  conveniently  passed.  They  are  frequently  employed  upon  the  palatal 
surfaces  of  bicuspids,  not  unfrequently  in  pairs,  each  one,  however,  be- 
ing separately  soldered  to  the  plate  with  each  end  free.  In  fitting  these 
partial  clasps  l)ear  in  mind  the  purpose  for  which  they  are  used,  so  as 
to  take  advantage  of  every  little  point  that  may  increase  their  usefulness. 
In  fitting  them  to  the  bicuspid  teeth,  to  make  them  fit  ver\'  accurately 
at  the  neck,  the  model  may  be  slightl\-  scraped  at  this  point  before  the 
clasps  are  adjusted,  so  that  they  will  spring  over  the  bulging  portion  of 
the  teeth  when  placed  in  the  mouth.  Let  the  strij)  of  plate  from  which 
they  are  made  be  amply  wide,  not  too  wide  for  proper  adjustment,  but 
quite  as  wide  as  the  tooth  is  long,  unless  it  is  of  unusual  length.  It  may 
be  that  when  the  plate  is  fitted  to  the  mouth  the  clasp  must  be  quite  nar- 
row, but  if  so  made  before  it  is  soldered,  being  so  lightl\-  held  by  the  in- 
vestment, it  will  probably  move  during  that  operation  sufficiently  to 
make  it  useless.    If  made  wide,  fitting  well  at  the  neck  of  the  teeth,  not 


CLASPS.  587 

only  is  a  change  of  position  less  likely  to  occur,  but,  if  when  fitting  the 
plate  in  the  mouth,  it  does  not  press  as  firmly  against  the  teeth  as  it 
should,  it  may  be  grasped  by  the  pliers  and  borne  outward  initil  it  does. 
The  free  edge  is  then  shaped,  being  cut  away  so  as  to  not  extend  beyond 
the  bulge  of  the  tooth  at  its  palatal  surface,  but  embracing  its  approx- 
imal  surfaces  nearly  to  the  cutting  edge.  It  not  unfrequently  happens 
that  partial  clasps  upon  bicuspid  teeth,  although  fitting  accurately, 
spring  the  plate  down  until  the  portion  extending  beyond  the  bulge  is 
removed,  they  then  take  hold  under  the  bulge,  and  hold  wdth  great 
firmness.  When  they  are  used  in  pairs,  the  ends  which  pass  into  the 
interspace  must  be  filed  thin,  so  that  both  clasps  will  pass  w^ell  in:  it 
is  a  mistake,  and  a  common  one,  to  make  one  clasp  short  at  this  point. 
When  soldering  these  partial  clasps  to  the  plate,  solder  sufficient  only 
to  make  the  union  secure,  both  ends  must  be  left  free.  Now  and  again 
stay  clasps  upon  the  bicuspid  teeth  on  both  sides  of  the  mouth  may  be 
used  to  advantage  to  wholly  sustain  a  plate.  Favorable  cases  are 
where  the  gums  have  receded  moderately  and  the  teeth  are  quite  firm. 
The  clasps  in  these  cases  pass  over  the  bulging  surfaces  of  the  teeth, 
and  impinging  lightly  upon  the  narrow^er  portion  of  the  teeth,  will 
hold  a  denture  satisfactorily  without  exerting  any  marked  outward 
pressure.  When  the  gums  are  normal,  and  the  root  portion  of  the  teeth 
not  exposed,  this  construction  is  seldom  admissable;  to  secure  firmness 
the  clasps  must  press  against  the  teeth;  the  denture  then  acts  like 
a  regulating  appliance,  and  in  a  little  while  the  teeth  are  pressed  out- 
ward and  no  longer  sustain  the  denture. 

Placing  and  fitting  clasps  requires  accurate  judgment;  while  the  gen- 
eral construction  is  the  same  in  all  cases,  the  endless  variety  of  condi- 
tions met  with  require  corresponding  variations.  First  consider  the 
object  the  clasp  is  designed  to  accomplish,  and  with  this  in  view,  pro- 
ceed with  its  construction. 

When  all  the  clasps  required  by  the  denture  are  fitted  to  the  teeth, 
they  are  adjusted  to  the  plate  in  the  following  manner.  Place  the  clasps 
on  the  model,  one  at  a  time,  and  file  away  the  plate  where  it  impinges 
upon  them  until  it  fits  in  place  on  the  model  with  all  the  clasps  in  position. 
The  next  step  is  to  cement  the  plate  and  clasp  together  so  that  they  can 
be  removed  from  the  model  to  invest  for  soldering.  In  ordinary  cases 
hard  resin-and-wax  cement  will  be  sufiicient;  for  difiicult  cases  shellac, 
being  stronger  and  more  rigid,  is  to  be  preferred.  In  using  either  it  is 
best  to  first  heat  the  plate  and  clasps  quite  hot  and  run  a  little  of  the 
cement  upon  them,  otherwise  the  cement  may  not  hold  firmly.  While 
the  plate  and  clasps  are  accurately  in  place  on  the  model  unite  them  with 
the  cement;  allow  a  few  minutes  for  it  to  chill,  then  carefully  remove 
them  from  the  model,  being  very  watchful  that  their  relative  positions 
are  not  changed.  The  cement  may  be  chilled  with  cold  water,  and 
is  then  made  more  rigid,  but  with  the  disadvantage  that  if  it  should  frac- 
ture in  removing  the  plate  from  the  model,  the  plate  and  clasps  must  be 
thoroughly  dried  before  the  cement  is  reapplied.  In  some  cases  it  is 
best  not  to  attempt  to  cement  all  the  clasps  at  the  same  time,  but  to  take 


588  SWAGED  METALLIC  PLATES. 

those  first  wliicli  may  readily  l)e  removed  with  the  jilate  from  the  model, 
solder  them,  and  then  adjust  the  others.  Those  elasps  in  whieh  the 
neek-fit  is  im|)ortaiit,  especiallN'  partial  clasps  upon  bicuspid  teeth,  may 
l)e  settled  in  |)()sition  upon  the  model  hy  a  few  sharp,  hut  not  severe, 
blows  with  the  ix-nch  hammer  just  prior  to  ccmentin<;-  them  to  the 
plate. 

Cases  are  met  with  occasional l.\  where  the  clasped  teeth  occupy  such 
a  j)osition  that  the  plate  and  clasp  cannot  be  removed  from  the  model 
without  the  cement  breaking.  In  such  cases  use  as  much  shellac  as 
possible,  let  it  get  quite  cold  and  rigid  so  that  it  will  break  without 
bending,  and  readjust  the  plate  and  clasp  after  their  removal  from  the 
model,  for  which  the  fractured  surfaces  furnish  a  fairly  trustworthy 
guide.  It  has  })een  suggested  that  if  the  case  camiot  be  removed  from 
the  model  it  cannot  be  placed  in  the  mouth.  While  this  is  true  of  ex- 
treme cases,  it  is  not  generally  so;  the  teeth  in  the  mouth  are  not  so 
rigidly  fixed  as  are  their  counterparts  on  the  plaster  model. 

After  the  plate  and  clasps  are  removed  from  the  model  they  are  in- 
vested for  soldering  in  a  batter  of  about  four  parts  plaster  to  five  of 
white  sand.  In  placing  the  investment  especial  care  should  be  taken 
to  so  imbed  the  clasps  that  they  will  not  be  drawn  in  toward  the  plate 
during  soldering;  and  also  that  the  relative  positions  of  the  clasps  and 
plate  are  not  changed  by  the  pressure  of  pressing  them  into  the  invest- 
ment. 

When  the  investment  is  thoroughly  hard,  the  cement  is  chipped 
away,  and  the  investment  so  carved  that  the  blowpipe  flame  can  readily 
reach  all  points  which  are  to  be  soldered.  Fill  with  plaster,  or  whit- 
ing mixed  w^ith  water  to  the  consistence  of  cream,  as  much  of  the  joint 
between  the  clasp  and  plate  as  it  is  intended  shall  remain  unsol- 
dered. It  is  not  desirable  at  this  stage  to  make  a  very  strong  union  be- 
tween the  clasps  and  plate,  but  simply  to  unite  them  at  some  point  at 
which  they  are  known  to  fit  the  teeth  and  which  will  be  included  in 
the  final  soldering.  It  is  desirable  that  they  be  left  as  free  as  possible 
so  as  to  permit  an  accurate  adjustment  when  the  plate  is  fitted  to 
the  mouth.  Now  scrape  the  surfaces  over  which  the  solder  is  to  flow, 
making  them  clean  and  bright,  coat  them  w^ith  borax,  lay  over  the 
joint  a  small  piece  of  plate  and  over  this  a  small  piece  of  solder. 
While  clasp  soldering  can  be  done  entirely  with  the  blow^  pipe  without 
previous  heating  of  the  investment,  it  is  a  decided  advantage  to  first 
make  the  investment  nearly  "red  hot".  If  this  is  not  done,  and  the 
blowpipe  flame  directed  immediately  tow^ard  the  part  to  be  soldered, 
the  uneven  heating  of  the  metal,  or  burning  away  of  the  investment  is 
apt  to  change  the  position  of  the  clasps,  or  by  displacing  the  plaster 
placed  in  the  joint  will  permit  the  solder  to  flow  further  than  is  intended. 
If  the  mass  of  the  investment  is  quite  hot  the  solder  flow^s  quickly, 
and  without  an  excessive  application  of  the  blowpipe  flame.  First 
use  a  broad  flame,  and  endeavor  to  heat  the  clasp  and  plate  equally. 
As  the  heat  approaches  that  required  to  fuse  the  solder,  use  a  more 
pointed  flame  and  concentrate  it  upon  the  parts  to  be  soldered,  but 


TRYING   THE  PLATE.  589 

not  directly  upon  the  solder.  If  the  solder  is  heated  more  than  the 
plate,  it  melts  into  a  ball,  and  it  is  then  difficult  to  make  it  flow.  When 
in  this  condition  more  heat  is  required,  and  sometimes  the  parts  are 
made  so  hot  that  when  it  finally  flows  some  of  the  surrounding  plate 
is  also  fused  with  it.  This  is  especially  apt  to  occur  if  there  is  a  large 
amount  of  solder  in  position.  This  is  one  reason  for  advising  a  small 
piece  at  first.  After  the  solder  has  once  bridged  the  joint  there  is  no 
difficulty  in  adding  more  to  make  the  joint  strong.  Sometimes,  when 
the  solder  has  "balled-up,"  as  this  condition  is  technically  termed,  it 
is  best  to  add  another  small  piece  and  endeavor  to  make  this  flow  over 
or  into  the  joint.  If  this  fails,  do  not  continue  to  add  solder,  but, 
with  a  pointed  steel  or  iron  rod,  say,  about  one-eighth  of  an  inch  in 
diameter,  and  ten  or  twelve  inches  long,  provided  with  a  suitable 
wooden  handle,  flatten  the  ball  of  solder  and  direct  it  into  place,  at  the 
same  time  by  skilful  application  of  the  blowpipe  flame  make  the  plate 
hot  at  the  point  over  which  the  solder  is  desired  to  flow.  The  sol- 
der always  tends  to  flow  to  the  hottest  point:  advantage  is  taken  of 
this  in  all  soldering  operations  and  its  flow  directed  by  the  skilful  ap- 
plication of  the  blowpipe  flame.  The  iron  or  steel  solder  director  is 
a  useful  tool.  Made  of  iron  or  steel,  it  is  not  apt  to  alloy  with  the  solder 
although  the  solder  tends  to  unite  with  it  slightly.  Before  beginning 
to  solder,  see  that  this  tool  is  at  hand  and  in  proper  order;  it  should  be 
filed  to  a  moderately  sharp  point,  and  all  adhering  solder  filed  off 
clean  so  as  not  to  contaminate  the  new  solder.  Now  and  asain 
moving  it  over  the  point  where  the  solder  should  flow  with  a  rub- 
bing motion,  or  with  a  wiping  motion  moving  the  molten  solder 
toward  the  joint  very  much  facilitates  a  successful  soldering. 

When  the  soldering  is  completed  there  is  no  objection  to  quickly 
cooling  the  plate  in  water  to  save  time.  It  is  then  "pickled"  in  acid 
and  cleaned  either  by  rubbing  with  white  sand  and  water  with  the  fin- 
gers, or  at  the  polishing  lathe  with  a  brush-wheel  and  pumice-stone. 
The  outer  ends  of  the  clasps  are  now  made  to  fit  the  teeth,  and  their 
upper  edges  filed  to  the  size  and  shape  desired,  leaving,  however,  a 
little  margin  for  any  changes  that  may  be  necessary  when  adjusting  the- 
plate  to  the  mouth.  It  is  well  to  remember  that  it  is  far  easier  to  take 
ofT  a  little  more  than  to  add.  After  rounding  and  smoothing  the  edges 
with  sand-paper,  if  the  plate  and  clasps  fits  the  cast  accurately,  it  is 
ready  for  adjustment  in  the  mouth. 


TRYING  THE  PLATE. 

After  the  plate  is  finished  on  the  model,  the  next  step  is  to  adjust  it  in 
the  mouth,  not  only  to  test  the  accuracy  of  the  impression,  but  also  to 
make  any  changes  that  may  be  required  to  secure  a  satisfactory  fit. 
This  is  more  important  with  the  plate  for  a  soldered  metallic  denture 
than  with  one  for  a  denture  that  is  either  cast  or  molded,  as  in  this  case 


590  SWAGED  METALLIC  PLATES. 

the  plate  is  not  a  mere  model,  but  is  designed  to  become  a  part  of  the 
denture,  and  should,  therefore,  be  made  to  fit  as  accurately  and  as 
comfortably  as  possible. 

In  an  upper  or  vacuum-chamber  plate,  after  relieving  any  points 
where  it  presses  unduly  into  the  soft  tissues,  or  if  it  is  a  partial  plate 
where  it  impinges  upon  any  of  the  remaining  teeth,  test  the  fit  in  much 
the  same  way  it  has  been  tested  on  the  model;  this  should  be  done  before 
testing  the  eti"ecti\eness  of  the  vacuum-chamber.  This  is  important. 
In  many  cases  a  moderately  strong  suction  will  hold  the  plate  so  firmly 
that  a  serious  misfit  may  pass  unnoticed,  and  the  mortifying  failure 
that  results  when  the  denture  is  finished  and  its  stability  tested  in  the 
act  of  mastication  will  probably  be  incorrectly  assigned  to  "warping 
during  soldering." 

Examine  closely  the  back  edge  of  the  plate.  In  some  mouths  the 
centre  is  quite  hard  and  rigid,  while  at  either  side  the  tissues  are  quite 
soft  and  yielding.  Changes  may  have  been  made  to  provide  for  this 
when  preparing  the  model  for  making  the  dies.  If  it  has  been  over- 
looked, or  the  changes  made  prove  not  sufficient  for  comfort  and  stabil- 
ity, any  needed  corrections  may  now  be  made.  Allowance  must  be 
made  for  the  changes  the  pressure  of  usage  will  make:  a  plate  that  fits 
quite  loosely  at  this  point  may  press  uncomfortably  hard  after  a  few 
days  u.se.  Any  needed  changes  in  this  respect  are  readily  made  at 
this  time  by  bending  the  edge  of  the  plate  with  the  pliers,  to  make  it 
press  harder,  or  to  relieve  undue  pressure.  If  there  is  much  difference 
between  the  fit  of  the  plate  on  the  model  and  in  the  mouth,  it  is  probably 
due  to  a  faulty  impression,  and  the  only  remedy  for  this  is  to  obtain  a 
better  one. 

When  the  central  hard  ridge  is  well  marked  and  the  plate  presses 
upon  it  unduly,  it  is  sometimes  necessary  to  reswage  the  plate  with  a 
thickness  of  paper  between  it  and  the  die  at  this  point,  or  an  additional 
piece  of  plate  may  be  soldered  back  of  the  chamber  and  extending  t(j 
the  edge  of  the  original  plate,  to  allow  for  filing  at  this  point  if  found 
necessar\'  after  the  denture  is  finished;  or  a  suflBcient  relief  may  be 
obtained  by  placing  a  few  thicknesses  of  paper  under  the  plate  on  the 
plaster  model  and  gently  striking  each  side  alternately  with  the  bench- 
hammer,  at  the  same  time  holding  the  plate  firmly  to  the  model.  If  the 
undue  pres.sure  is  at  the  extreme  edge  of  the  plate,  it  may  be  relieved 
with  the  pliers,  but  it  is  more  frequently  .so  far  in.side  of  the  edge  that 
they  are  not  available.  In  a  few  cases  the  mouth  is  intolerant  of  a 
plate,  its  presence  causing  severe  nausea  even  though  it  does  not  en- 
croach upon  the  soft  palate.  Persistent  use  will  often  overcome  this, 
but  not  always.  Usually  the  central  portion  of  the  mouth  is  more 
sen.sitive  than  is  the  alveolar  ridge,  and  advantage  may  be  taken  of 
this  to  secure  a  more  comfortable  plate  by  extending  it  far  back  on 
either  side  and  leaving  the  roof  of  the  mouth  free,  or,  in  other  words, 
making  it  horseshoe-shaped. 

Occasionally  the  edges  of  the  vacuum-chamber  press  too  hard;  this 
is  easilv  relieved,  and  its  correction  had  better  be  left  until  the  denture 


TRYING  THE  PLATE.  59I 

is  finished;  the  smoothing  of  these  edges  in  the  final  poHshing  may  be 
all  that  is  needed. 

Examine  the  edges  of  the  plate  and  see  that  they  are  in  close  contact 
with  the  gums,  and  that  there  is  sufficient  room  during  the  various 
movements  of  the  mouth  for  the  fra?num  in  front,  and  the  "strings"  on 
either  side  just  back  of  the  canine  teeth.  In  partial  cases  see  that  the 
edges  fit  snugly  against  the  remaining  teeth.  In  partial  cases,  when 
a  vacuum  is  produced,  see  that  the  plate  fits  closely  to  the  gum  where 
Jt  extends  through  the  interdental  spaces;  it  not  infrequently  happens 
that  a  vacuum-cavity  plate  is  slightly  displaced,  when  drawn  firmly  to 
place;  usually  it  is  brought  forward.  This  is  more  likely  to  happen  with  a 
small  plate  in  which  the  vacuum-chamber  is  well  in  front;  in  partial 
cases  this  movement  is  occasionally  so  marked  that  it  is  necessary  to 
take  an  impression  \\'ith  the  plate  in  place  in  order  to  obtain  an  accurate 
guide  for  arranging  the  teeth. 

In  full  lower  plates,  first  see  that  they  fit  solidly,  and  are  without  rock 
or  spring,  that  the  edges  are  in  contact  with  the  gum  at  all  points,  and 
yet  do  not  press  unduly.  The  lingual  edge  immediately  back  of  the 
incisor  teeth,  and  the  lingual  aspect  of  the  distal  ends,  are  points  that 
frequently  require  bending  inward.  These  points  are  often  markedly 
undercut,  and  are  points  where  the  plate  is  apt  to  be  inaccurate  owing 
to  inaccuracy  of  the  model,  inaccuracy  of  the  die,  or  failure  to  thoroughly 
swage  the  piate  into  the  undercut.  In  cases  where  the  undercut  is  quite 
marked  the  plate  cannot  be  swaged  accurately  by  the  counter-die  alone. 
A  blunt  pointed  chisel  or  chaser  made  of  bone  (a  tooth-brush  handle 
answers  admirably),  and  at  times  a  pair  of  pliers,  will  be  required  to 
make  the  plate  fit  accurately  at  these  points.  Next  make  sure  that  there 
is  ample  room  for  the  franum  of  the  tongue  when  the  tongue  is  raised 
as  in  swallowing,  and  that  the  back  part  of  the  plate  does  not  encroach 
upon  the  cheek,  or  interfere  with  the  movements  of  the  tongue.  I^ower 
plates  are  frequently  made  wide  at  the  distal  ends,  under  the  idea  that 
the  increased  width  adds  to  their  stability  and  comfort.  This  is  seldom 
the  case ;  but  few  mouths  will  tolerate  a  lower  plate  wider  at  the  ends 
than  the  face  of  the  alveolar  ridge. 

In  partial  lower  plates  see  that  the  plate  fits  closely  to  the  teeth  upon 
which  it  extends.  Partial  lower  plates  should  be  tried  in  the  mouth 
and  accurately  adjusted  before  the  reinforcing  pieces  are  added,  so  that 
any  changes  found  necessary  can  be  readily  made;  after  the  plate  is 
"doubled,' '  "wired,"  or  "reinforced,"  it  is  very  difficult  on  account  of  the 
stiffness  imparted  by  the  additional  thickness  and  by  the  solder,  to 
make  any  material  change  in  its  shape. 

The  clasps  on  all  plates  retained  wholly  or  in  part  by  clasps  should 
be  filed  into  shape  and  bent  around  the  teeth  as  far  as  they  are  intended 
to  go  at  this  stage,  but  should  not  be  fitted  closely  to  the  teeth,  except  so 
far  as  they  are  intended  to  be  soldered.  To  permit  the  ready  removal 
of  the  plate  from  the  mouth  it  is  best  to  leave  the  clasps  rather  loose 
until  the  denture  is  finished,  especially  if  it  is  desired  to  adjust  the  teeth 
in  the  mouth  before  they  are  soldered  to  the  plate. 


592  SWAGED  METALLIC  PLATES. 

In  adjusting];  the  clasps  especial  attention  is  needed  to  so  shape  the 
ends  that  they  will  hold  firmly,  and  yet  as  far  as  possible  be  out  of  the 
way  and  out  of  si<i:ht,  and  at  the  same  time  be  confined  to  those  portions 
of  the  tooth  least  liable  to  injury.  In  bicuspid  and  canine  teeth  there 
is  usually  a  more  or  less  marked  curve  of  the  labial  or  buccal  face,  and 
frequently  these  teeth  are  markedly  wedge-shaped.  "When  this  is  the 
case,  let  the  clasps  be  sufficiently  wide  on  the  approximal  surfaces,  that 
after  the  plate  sinks  down  a  little  as  all  plates  do  after  they  have  been, 
worn  a  short  time,  they  will  still  embrace  the  widest  part  of  the  tooth, 
and  the  ends  that  extend  on  the  buccal  or  labial  surface  may  be  cut 
away  from  the  upper  edge  fthc  edge  nearest  the  occlusal  surface  of 
the  tooth),  so  as  to  spring  over  the  curve  of  that  face  of  the  tooth.  This 
not  only  gives  a  firmer  hold,  but  makes  it  far  less  conspicuous.  In  all 
cases,  no  matter  how  much  the  clasp  may  require  to  be  cut  away  to 
avoid  impinging  upon  the  gum  or  from  any  other  cause,  be  careful  to 
so  shape  it  that  the  strongest  part  shall  l)e  where  it  is  soldered  to  the 
plate,  and  that  it  tapers  ofT  from  this  point  to  either  end,  as  previously 
suggested. 

In  upper  plates  the  clasps  are  designed  mainly  to  hold  the  plate  firm- 
Iv  to  the  roof  of  the  mouth;  in  lower  plates  their  chief  function  is  to 
hold  the  plate  in  position,  to  counteract  the  tendency  in  these  plates  to 
slide  backward,  and  also  where  hooks  or  catches  are  added,  to  relieve 
the  pressure  upon  the  gums.  They  also  hold  the  plate  down,  but  this 
is  usually  their  least  important  function.  This  distinction  in  function 
between  upper  and  lower  clasps  should  be  borne  in  mind  when  making 
or  adjusting  them. 

There  are  many  minor  points  to  be  considered  when  trying  in  a  plate 
that  are  self-suggestive,  the  points  enumerated  are  the  more  important 
ones,  and  are  mainly  concerned  with  ac(Hiracy  of  adaptation  and  the 
patient 's  comfort.  Beyond  this,  especially  in  partial  cases,  much  may 
be  observed  that  will  be  of  assistance  in  completing  the  work.  Inaccu- 
racies of  the  model  that  impair  its  usefulness  as  a  guide  in  arranging  the 
teeth  should  be  corrected;  the  condition  of  the  gums  upon  which  the 
teeth  are  to  rest  should  be  noted,  and  the  model  carved  as  ma>-  seem 
necessary,  so  that  the  artificial  teeth  or  gums  will  properly  blend  with 
the  natural  ones.  Any  marked  peculiarities  to  be  considered  in  arrang- 
ing the  teeth  should  be  noted  and  marked  upon  the  model,  so  that  later 
they  may  not  be  overlooked. 

The  shade  may  now  be  selected,  the  kind  and  character  of  teeth  de- 
cided upon,  and  the  bite-impression  taken. 

TAKING  THE  BITE. 

Apart  from  the  fact  that  in  full  soldered  dentures  the  operation  tech- 
nically known  as  "taking  the  bite,"  is  conducted  with  the  plates  that 
are  ti)  be  used  in  constructing  the  denture,  and  not  on  temporarv  trial 
plates,  as  is  the  case  with  molded  or  cast  dentures,  the  procedure  is  pre- 


SELECTING  THE  TEETH.  593 

ciscly  the  same  for  soldered,  cast,  and  molded  dentures.  In  partial 
cases  it  ma>-  be  done  when  the  impression  is  taken  or  immediately  after 
the  plate  is  fitted  to  the  mouth,  and  while  it  is  still  in  position,  as  may 
be  most  convenient.  In  a  few  exceptional  cases  where  the  bite  is  very 
close,  or  where  the  occluding  teeth  interfere,  a  more  satisfactory  bite 
may  sometimes  be  obtained  if  taken  with  the  plate  in  position;  mainly 
because  there  is  less  risk  of  misplacing  it  upon  the  model  prior  to  making 
the  articulating  model.  The  method  of  taking  the  bite,  the  precautions 
,to  be  observed  to  secure  accuracy,  and  the  construction  of  the  articu- 
lating model,  are  fully  considered  in  Chapter  X. 

SELECTING  THE  TEETH. 

As  the  general  subject  of  selecting  teeth  is  elsewhere  in  this  work  con- 
sidered at  length,  it  is  unnecessary  in  this  place  to  do  more  than  briefly 
consider  those  purely  mechanical  matters  especially  concerned  with 
selecting  teeth  for  soldered  dentures.  Inasmuch  as  the  teeth  of  a  sol- 
dered denture  must  rest  upon  and  fit  closely  to  the  plate,  more  care  is 
needed  in  their  selection  than  in  selecting  teeth  for  a  molded  or  cast 
denture.  In.  the  latter  case,  but  little  is  required  beyond  satisfying  the 
artistic  requirements  of  the  case;  as  the  plate  is  made  to  fit  the  teeth 
after  they  are  finally  arranged  in  position.  In  a  soldered  denture,  on 
the  contrary,  the  teeth  are  accurately  fitted  to  the  plate  by  means  of 
various  forms  of  grindstones,  and  in  addition  to  satisfying  the  equally 
exacting  artistic  requirements,  the  purely  mechanical  problems  this  in- 
volves must  be  considered  when  the  teeth  are  selected.  When  plain 
teeth  are  used  this  involves  but  little  more  than  sufficient  extra  length 
to  allow  the  teeth  to  fit  the  plate  solidly  throughout  the  area  of  con- 
tact between  the  tooth  and  the  plate,  The  selection  of  gum-teeth  is 
more  complicated.  There  must  be  sufficient  body  back  of  the  gum  to 
permit  the  porcelain  to  accurately  fit  the  plate  over  the  whole  area 
of  contact  when  the  tooth  is  in  its  proper  position.  Considerations  of 
cleanliness  as  w^ell  as  of  strength  calls  for  this  accurate  adaptation 
of  the  porcelain  to  the  metallic  plate.  The  usual  form  of  teeth  made 
especially  for  soldered  dentures  requires  a  metallic  backing  reaching 
nearly  to  the  cutting  edge.  In  a  close  bite  this  must  be  considered, 
especially  when  selecting  anterior  teeth  for  an  upper  denture,  and  teeth 
selected  sufficiently  thin  to  permit  this  without  making  the  tooth  un- 
duly prominent. 

The  position  of  the  pins  must  also  be  noted.  Teeth  for  plate-work 
usually  have  two,  arranged  either  transversely  or  perpendicularly,  and 
are  technically  known  respectively  as  cross  and  straight  pins.  Very  large 
or  very  long  teeth  have  three  or  four,  usually  vertical.  The  cross  pin 
teeth  are  designed  for  cases  of  close  bite,  and  now  and  again  serve  a 
useful  purpose.  They  should  be  avoided  wherever  possible,  as  they 
are  inherently  weak  from  the  following  reasons:  first,  the  position  of 
the  pins  weakens  the  tooth  at  the  point  where  it  is  most  liable  to  break 


594  SWAGED  METALLIC  PLATES. 

from  stress  of  use  or  strain  clurint;  soldering;  second,  when  arranged 
in  place  both  pins  are  brought  near  the  plate,  making  the  strain  upon 
the  pins  and  the  porcelain  greater  on  account  of  the  increased  leverage 
between  the  pins  and  the  cutting  edges,  and  furthermore,  this  strain,  in 
time  stretches  the  metal  of  which  the  pins  are  made  and  permits  a 
slight  rocking  movement  of  the  tooth  which  causes  the  pins  to  break 
between  the  backing  and  the  tooth.  They  are  least  objectionable  in 
short  molar  and  bicuspifl  teeth,  and  in  anterior  teeth  very  broad  in 
proportion  to  their  length.  It  is  a  common  error  to  always  select 
cross  pin  teeth  for  a  close  bite.  In  all  such  cases  the  backings  should 
be  extended  to  near  the  cutting  edges,  so  that  they  will  relieve  the 
teeth  of  part  of  the  strain,  AYhen  this  is  done  there  is  no  advantage 
whatever  in  cross  pins. 

The  straight  pin  teeth  are  more  reliable,  mainly  from  the  fact  that  the 
upper  pin  is  closer  to  the  point  at  which  the  force  is  applied,  and  the 
leverage  upon  it  is,  therefore,  less. 

The  position  of  the  pins  is  also  varied.  Some  teeth  are  made  with 
the  pins  nearer  the  cutting  edges,  than  are  others,  and  in  some,  the  pins 
are  placed  nearer  together.  Advantage  should  be  taken  of  this,  and 
teetli  selected  with  the  pins  in  the  best  position  to  resist  the  strain  in- 
cident to  constructing  the  denture  and  the  strain  of  constant  use.  Pins 
near  together  are  much  more  liable  to  cause  fracture  of  the  tooth  during 
soldering,  and  do  not  so  well  resist  the  strain  of  constant  use;  straight 
pins  so  placed  that  they  come  near  to  the  plate  when  the  tooth  is  in 
position,  while  there  is  considerable  space  between  the  upper  pin  and 
the  occlusal  edge,  provided  that  the  backing  can  be  extended  so  as  to 
protect  the  tooth,  are  to  be  avoided;  in  all  such  cases  teeth  with  pins 
better  placed  can  quite  as  readily  be  used.  While  very  thin  teeth  should 
be  avoided  on  account  of  their  weakness,  where  they  are  not  especially 
required,  very  thick  teeth  are  objectionable  on  account  of  their  clumsi- 
ness. Porcelain  teeth  mounted  upon  a  molded  or  cast  base  are,  as  a 
rule,  better  supported  than  are  those  upon  soldered  metallic  plates;  they 
are  less  strained  during  the  process  of  construction;  their  initial  strength 
and  their  ability  to  resist  strain  is,  therefore,  less  important. 

Close  attention  to  detail,  a  careful  study  of  the  varied  strains  porce- 
lain teeth  are  subjected  to  during  the  process  of  constructing  a  denture 
and  thereafter,  should  be  brought  to  bear  in  selecting  teeth  for  each 
individual  case.  The  artistic  and  the  mechanical  requirements  are 
equally  important,  and  it  is  important  to  know  the  resources  of  good 
workmanship  in  securing  the  best  result  when  either  one  must  be 
sacrificed.  The  large  number  of  porcelain  tooth  makers,  the  individ- 
ual peculiarities  and  the  variety  of  their  products,  are  decided  helps  in 
obtaining  that  which  is  best  for  each  case.  This  suggests  the  import- 
ance of  keeping  in  touch  with  that  which  they  have  to  offer  in  the  im- 
portant matter  of  selecting  teeth. 


ARRAXGIXG  AXD  FITTING     THE  TEETH.  595 


THE  ARRANGEMENT  AND  FITTING  OF  THE  TEETH. 

The  arrangement  and  fitting  of  teeth  to  soldered  metalhc  dentures 
requires  much  more  care  than  does  the  same  operation  in  the  con- 
struction of  cast  or  mokled  dentures!  Accurate  fitting  of  the  tootli  to 
the  metal  phite  is  demanded  on  the  score  of  strength  and  of  cleanhness. 
If  the  tooth  does  not  rest  sohdly  upon  the  plate  the  whole  of  the  stress 
■due  to  usage  is  borne  by  the  platinum  pins;  at  times  this  results  in  the 
pins  being  broken,  or  they  may  be  stretched  and  so  reduced  in  calibre 
that  they  draw  out  of  the  porcelain.  "When  this  occurs  the  fault  is  usu- 
ally ascribed  to  careless  heading  of  the  pins  by  the  manufacturer;  the 
fact,  however,  that  the  pins  in  these  cases  fit  the  holes  in  the  porce- 
lain loosely,  and  that  if  seen  before  they  have  separated  from  the  teeth 
are  found  so  reduced  in  diameter  that  they  freely  move  while  still  held 
by  the  head  imbedded  in  the  tooth  is  conclusive  that  the  tooth  maker 
is  not  in  fault.  \Miile  it  is  impossible  to  secure  absolute  contact  between 
the  plate  and  the  tooth,  every  effort  should  be-  made  to  secure  accurate 
adaptation,  leaving  as  little  space  for  the  accumulation  of  offensive  mat- 
ter between  the  tooth  and  the  plate  as  possible. 

The  artistic  problems  of  tooth  arrangement  are  very  much  the  same 
with  all  kinds  of  dentures;  the  mechanical  procedure,  however,  by 
which  this  is  attained,  and  the  special  mechanical  problems  involved 
are  varied.  It  is  to  the  latter,  the  special  requirements  of  tooth  ar- 
rangement for  soldered  dentures,  that  attention  is  now  directed. 

Entire  Dentures. — To  properly  adapt,  arrange  to  the  best  advantage, 
and  to  correctly  finish  a  full  denture  of  gum-plate  teeth  is  "one  of  the 
most  difficult  operations  in  prosthetic  dentistry.  Each  tooth  must  be 
separately  adjusted  and  fitted  in  position  so  as  to  secure  the  proper 
position  and  spacing  of  the  tooth-part  and  at  the  same  time  properly 
contour  the  gum  portion  without  breaks  or  offsets;  to  do  this  and  to  pro- 
\ade  against  accidents  in  soldering,  and  to  accurately  fit  the  teeth  to  the 
plate,  tests  to  the  utmost  the  w^orkman's  skill.  To  describe  how  this  is 
to  be  accomplished,  beyond  indicating  the  proper  use  of  the  mechanical 
means  employed,  is  equally  a  difficult  task.  It  must  be  borne  in  mind 
that  in  plate  work,  teeth  are  fitted  by  grinding  from  their  substance; 
nothing  can  be  added  to  replace  that  which  has  been  needlessly  remo  ved. 
This  will  suggest  the  importance  of  first  fixing,  definitely,  the  position 
of  each  tooth  as  nearly  as  can  be  done,  by  roughly  arranging  a  series 
of  teeth  approximately  in  position;  then  to  proceed  carefully,  making 
such  corrections  as  may  be  needed  in  slant,  length,  fulness,  and  spac- 
ing; finally  finish  the  joints  between  the  teeth  and  make  the  gum  por- 
tion form  an  even  surface.  There  are  three  points  to  be  first  determined 
when  making  this  preliminary  arrangement;  first,  and  first  in  im- 
portance, the  median  line.  This  should  be  accurately  marked  when 
taking  the  articulation  while  the  plates  are  in  the  mouth,  and  should 
coincide  with  the  median  line  of  the  face.  To  correct  any  error  in  its 
position,  however  slight,  may  involve  changing  the  position  of  every 


596  SWAGED  METALLIC  PLATES. 

tooth  upon  the  denture,  and  if  this  is  done  after  the  teeth  have  been 
accurately  arran^^cd,  it  will,  in  many  cases,  imi)air  beyond  remedy  the 
adaptation  of  the  teeth  to  the  plate.  A  tooth  accurately  fitted  in  one 
position  can  seldom  be  as  accurately  fitted  to  another.  If  there  is  any 
doubt  about  the  median  line  being  accurately  marked  upon  the  model, 
hold  the  case  so  that  a  line  drawn  through  the  centre  antero-posteriorly  is 
exactly  perpendicular:  if  the  central  teeth  are  in  their  proper  positions, 
the  bicuspids  will  be  directly  opposite  to  each  other.  There  are  oc- 
casional exceptions  to  this  rule,  but  it  is  so  generally  reliable  that  it  is 
well  to  regard  with  suspicion  any  centre  mark  that  does  not  conform 
to  it,  and  to  ascertain  beyond  doubt  its  correctness  before  so  far  grind- 
ing the  teeth,  that  their  position  cannot  be  changed  without  injury. 
The  two  other  points  are  the  junctions  of  the  canines  and  bicuspids  of 
each  side.  This  point  marks,  first,  the  change  in  contour  line  of  the 
denture  from  the  anterior  arch  to  its  abutments,  the  posterior  teeth, 
which  are  from  this  point  arranged  in  a  straight  line;  and  second,  a 
change  in  the  slant  of  the  teeth,  from  a  marked  leaning  toward  the 
median  line  of  the  anterior,  teeth  to  the  nearly  perpendicular  position 
of  the  bicuspids  and  molars.  It  also  determines  accurately,  the  space 
to  be  occupied  by  the  six  anterior  teeth.  This  joint,  that  between  the 
canine  and  bicuspid  teeth,  is,  in  gum  plate  teeth,  by  far  the  most  dif- 
ficult to  make  of  any  in  the  denture,  the  artistic  blending  of  the  gums 
of  the  anterior  and  posterior  teeth  depends  upon  the  workman's  skill, 
whereas  in  gum  block  sections  it  is  provided  for  by  the  tooth  maker. 

The  first  step  in  arranging  a  set  of  plate  teeth  is  to  clean  thoroughly 
the  platinum  pins,  especially  to  remove  from  them  a  slight  coating  of 
porcelain  acquired  when  the  teeth  are  made,  being  careful  that  this  is  done 
close  up  to  the  body  of  the  tooth,  where  a  little  cone  of  porcelain  is  fre- 
quently found  encircling  the  base  of  the  pin.  See,  also,  that  the  pins  are 
straight,  at  right  angles  to  the  tooth,  and  parallel  to  each  other.  This 
can  be  done  at  this  stage  better  than  later,  as  it  not  unfrequently  hap- 
pens that  a  tooth  may  be  ground  away  so  close  to  a  pin  that  while  its  hold 
in  the  porcelain  is  not  materially  weakened,  a  slight  strain  upon  it  might 
break  it  out  and  ruin  the  tooth. 

If  the  wax  or  modelling  composition  used  in  taking  the  articulation 
has  been  carefully  carved  to  represent  the  desired  length  and  fulness  of 
the  upper  and  lower  denture,  that  on  the  lower  plate  may  be  used  as 
a  guide  in  the  preliminary  arrangement  of  the  upper  teeth,  the  wax,  or 
composition,  for  the  time  being  taking  the  place  of  the  lower  denture. 
The  upper  teeth  are  usually  arranged  first,  as  they  are  more  important  in 
giving  expression.  Now,  arrange  upon  the  upper  plate  a  layer  of  adhe- 
sive wax,  not  too  massive,  and  yet  sufficient  in  amount  to  hold  the  por- 
celain teeth  securely  when  their  pins  are  pressed  into  it.  It  is  not  desir- 
able that  this  adhesive  wax  should  be  at  all  brittle,  and  yet  it  should 
be  sufficiently  hard  to  hold  its  form  well,  and  to  hold  the  teeth  in  position 
sufficiently  firm  when  trying  in  the  mouth,  when  with  the  wax  spatula, 
it  is  fused^  around  their  pins.  This  layer  of  adhesive  wax  should  ex- 
tend nearly  to,  but  not  to  touch  the  wax  on  the  lower  plate,  and  should 


ARRANGING  AND  FITTING  THE  TEETH.  597 

be  molded  to  the  general  contour  desired  in  the  teeth,  allowance  being 
made  for  their  thickness. 

On  this  layer  of  wax  arrange  the  eight  anterior  teeth,  first  placing  in 
position  the  central  incisors,  grinding  them  sufficiently  only  to  get  them 
approximately  in  position.  These  are  followed  by  the  lateral  incisors, 
the  canines,  and  the  first  bicuspids;  by  arranging  the  teeth  in  pairs 
when  placing  them  roughly  in  position,  and  also  when  adjusting  them 
finally,  one  has  a  better  idea  of  the  general  effect.  During  this  part 
of  the  work,  accuracy  in  making  the  articulating  model  will  be  appre- 
ciated. If  an  articulator  is  used,  it  is  important  that  the  centre  line  of  the 
articulator  and  the  centre  line  of  the  denture  coincide ;  and  also  that  the 
occlusal  line  and  the  top  and  bottom  of  the  articulator  are  all  parallel. 
In  order  to  see  that  the  teeth  have  a  proper  slant,  and  that  the  occlusal 
line  gives  to  the  teeth  of  each  side  the  right  length,  the  workman  holds 
the  articulating  model  before  him  on  a  level  with  the  eye,  and  the  eye  is 
instinctively  guided  in  judging  of  these  matters  by  the  upper  and  lower 
fines  of  the  articulator.  If  the  denture  has  been  misplaced  in  the 
articulator,  or  the  articulating  model  is  defective  in  these  respects,  it  is 
best  to  correct  the  fault  as  far  as  it  can  be  corrected  before  proceeding. 
With  these  eight  teeth  roughly  in  position,  and  the  place  the  canine 
tooth  should  occupy  noted,  the  amount  of  joint-grinding  necessary  to 
bring  the  artificial  teeth  to  their  correct  anatomical  position  is  readily 
determined.  This  amount  is  to  be  divided  among  the  five  joints.  In  this 
preliminary  arrangement  let  the  teeth  be  a  trifle  too  long  to  allow  for  a 
slight  shortening  when  they  are  accurately  fitted  to  the  plate.  Note  care- 
fully the  surface  of  that  portion  of  the  plate  upon  which  the  teeth  and 
artificial  gums  rest.  If  this  is  markedly  uneven,  but  little  grinding 
should  be  done  until  the  spacing  is  well  advanced.  If  a  tooth  is 
hollowed  out  to  fit  over  a  prominence,  and  is  afterward  moved  forward, 
it  is  quite  likely  that  the  hollowed  out  portion  will  remain  a  vacant 
space.  Note  also  that  nearly  all  single  gum  plate  teeth  have  the  sides 
of  the  gum  portion  slightly  rounded;  the  object  of  this  is  to  provide  a 
means  for  making  the  gums  even  when  the  teeth  are  fitted  to  an  irreg- 
ular surface,  or  when  the  tooth  portion  is  arranged  slightly  unevenly. 
When  it  is  desired  that  a  tooth  should  set  in  more  than  its  neighbor, 
this  can  be  accomplished  without  making  a  noticeable  offset  by  grinding 
more  from  the  side  of  its  gum  when  spacing.  Advantage  is  taken  of 
this  in  making  the  joint  between  the  canine  and  bicuspid;  quite 
frequently  it  is  necessary  to  grind  no  more  from  the  canine  gum 
than  to  make  the  edge  smooth,  removing  all  that  is  necessary  to  close 
properly  the  joint  from  the  bicuspid  gum  in  order  to  place  the 
bicuspid  in  its  normal  position,  that  is,  slightly  less  prominent  than  the 
canine.  And  again,  to  bring  the  tooth  portion  of  these  two  teeth  into 
proper  relation,  it  is  not  unfrequently  necessary  in  order  to  make  the 
gums  blend,  to  make  the  joint  at  a  slight  angle,  instead  of  in  line  with 
the  axis  of  the  teeth. 

When  these  eight  teeth  are  roughly  fitted  into  position,  the  wax  guide 
b  removed  from  the  lower  plate,  and  the  anterior  eight  lower  teeth  are 


51)8  SWAGED  METALLIC  PLATES. 

in  like  manner  roughly  fitted  in  place.  If  the  upper  and  lower  teeth  are 
of  proper  widtli,  and  properly  spaced,  the  points  of  the  upper  canines 
will  rest  between  the  points  of  the  lower  canines  and  first  bicuspids. 
They  should  be  made  to  take  this  position  during  this  rough  fitting 
while  spacing  the  teeth.  Up  to  this  stage  the  teeth  will  usually  retain 
their  position  sufficiently  well  by  simply  pressing  tlieir  pins  into  the  wax; 
some  little  care  is  required,  however,  to  prevent  the  central  incisors 
from  being  pushed  from  the  median  line,  and  to  avoid  displacing  the 
upper  teeth  outward  while  arranging  the  lower  teeth. 

When  the  eight  anterior  teeth  on  the  upper  and  lower  plate  are  of 
exactly  the  right  length;  the  overbite  as  it  is  intended  to  be;  the  curve  of 
the  arch,  the  fulness,  so  far  as  the  tooth  portion  is  concerned ;  and  the 
general  expression  quite  satisfactory,  they  may  be,  for  the  time  being, 
considered  finished.  The  gum  portion,  especially  of  the  upper  denture, 
may  be  a  little  too  prominent,  and  the  spaces  a  trifle  too  wide;  it  is 
well  that  they  should  be,  to  permit  a  final  and  more  accurate  adapta- 
tion of  the  gum  portion  to  the  plate,  and  a  consequent  closing  of  the 
spaces.  The  six  anterior  teeth  of  each  denture  are  now  firmly  "waxed" 
in  position  so  that  they  will  not  be  disturbed  while  the  posterior  teeth 
are  being  arranged.  This  is  done  by  passing  a  heated  wax  spatula  on 
each  side  of  the  pins  over  each  tooth,  beginning  with  the  centrals. 
This  spatula  should  be  sufficiently  hot  to  melt  thoroughly  the  wax  and 
heat  slightly  the  pins  and  the  surface  of  the  teeth;  the  teeth  being  held 
in  place  while  this  is  being  done  by  curving  the  fore  finger  of  the  left 
hand  around  them.  The  spatula  is  first  passed  between  the  centrals, 
and  held  until  the  wax  is  thoroughly  melted,  when  it  is  withdrawn,  the 
denture  in  the  meantime  being  so  held  that  the  wax  will  not  flow  from 
its  position.  When  this  wax  has  chilled,  the  same  procedure  is  repeated 
between  the  centrals  and  laterals,  and  between  the  laterals  and  canines; 
in  each  case  the  wax  must  be  allowed  to  chill  before  proceeding,  other- 
wise the  teeth  would  become  displaced. 

The  lower  posterior  teeth  of  each  side  are  now  roughly  fitted,  and 
then  the  upper  bicuspids  and  molars,  with  especial  care  to  make  them 
normally  articulate  by  proper  spacing.  The  usual  form  of  the  gum  por- 
tion of  plate  bicuspids  and  molars  tends  to  make  them  assume  an  .in- 
ward curve  owing  to  the  lingual  side  being  made  narrower  so  as  to  save 
grinding  in  making  the  joints.  This  must  be  guarded  against.  When 
the  posterior  teeth  of  each  side  are  satisfactorily  arranged,  they  are  to  be 
"waxed"  firmly  in  place  as  were  the  front  teeth,  and  it  is  well  at  this 
stage  to  adjust  them  in  the  mouth.  Little  changes  may  be  needed  that 
can  now  readily  be  made  without  detriment  that  if  attempted  after  the 
final  adjustment  might  result  in  imperfect  joints.  Prior  to  this,  the 
teeth  should  be  securely  waxed;  more  wax  being  added  where  needed 
and  the  whole  made  neat  and  smooth.  A  little  wax  run  in  along  the 
ends  of  the  gums  at  the  outer  edge  of  the  plate  assists  very  much  in 
holding  them  securely.  There  is  always  a  risk  that  the  patient  may,  in- 
advertently, close  a  little  too  firmly;  this  will  displace  them  if  the  cement- 
ing with  wax  is  not  thoroughly  done. 


ARRANGING  AND  FITTTNG   THE  TEETH.  599 

After  making  any  corrections  suggested  while  trying  the  teeth  in  the 
mouth,  they  should  be  carefully  gone  over  and  the  final  fitting  of  the 
teeth  to  the  plate,  eN'ening  of  the  gums,  and  accurate  adjustment  of 
the  joints  receive  needed  attention. 

The  arrangement  of  the  teeth  is  now  complete. 

Arrangement  and  Fitting  of  Teeth  to  an  Upper  or  Lower  Denture. — 
In  arranging  the  teeth  to  an  upper  or  lower  denture,  the  same  general 
plan  is  followed  as  in  arranging  a  full  denture.  If  the  antagonizing 
teeth  are  markedly  irregular,  some  little  ingenuity  may.  be  required 
when  fitting  gum  teeth  to  make  the  occlusal  edges  of  the  anterior 
artificial  and  natural  teeth  fit  sufficiently  close  to  prevent  lisping,  or 
to  prevent  a  hissing  sound  when  pronouncing  certain  letters,  and  at 
the  same  time  preserve  a  desired  alignment  of  the  artificial  teeth  and 
gums.  This  is  more  readily  accomplished  when  plain  teeth  are  used 
as  it  is  not  complicated  by  the  artificial  gums.  Nevertheless,  much 
care  is  required  in  these  cases  to  make  plain  teeth  fit  solidly  upon  the 
plate.  The  same  precautions  are  required;  the  teeth  must  first  be 
approximately  adjusted  to  position,  the  grinding  cautiously  done,  and 
the  final  accurate  fitting  deferred  until  the  position  of  the  teeth  has 
been  definitely  determined.  The  anterior  lower  teeth,' on  account  of 
their  narrowness  are  more  readily  fitted;  they  are  less  concerned  in 
expression,  and  the  artistic  requirements  are  less  exacting. 

Gum  and  Plain  Teeth. — Whether  to  use  gum  or  plain  teeth  in  con- 
structing soldered  plate  work  is  decided  by  the  same  general  rules  ap- 
plicable to  all  dentures.  Gum  teeth  are  required  to  restore  a  normal 
fulness,  or  to  hide  the  plate.  In  some  cases  where  gum  teeth  are  re- 
quired^  and  where  it  is  desired  to  have  as  little  fulness  as  possible,  the  gum 
teeth  may  be  set  directly  upon  the  natural  gum,  the  plate  being  cut  away 
to  allow  them  to  do  so.  It  is  seldom  necessary  to  cut  it  away  further 
back  than  the  canine  teeth.  The  plate  should  be  allowed  to  extend  as 
far  under  the  teeth  as  possible,  the  edge  of  the  plate  being  beveled  quite 
thin  so  that  after  the  teeth  are  soldered  it  can  be  burnished  up  to  them 
and  a  close  joint  made.  It  is  a  common  fault  to  cut  the  plate  away  too 
much,  not  only  depriving  the  teeth  of  the  support  it  should  give,  but 
impairing  the  adhesion  and  bringing  the  edge  so  directly  under  the 
solder  that  it  is  too  rigid  to  burnish  up  to  the  teeth.  To  avoid  this,  if 
the  teeth  have  been  recently  extracted  and  the  alveolar  border  is  quite 
uneven,  it  is  allowable  to  trim  down  the  more  prominent  portions; 
even  in  cases  where  resorption  is  well  advanced,  the  portion  of  the  model 
against  which  the  artificial  teeth  fit  may  be  somewhat  freely  carved  or 
rubbed  down  M^ith  fine  sand-paper.  It  is  desirable  that  in  the  mouth  the 
artificial  gum  should  fit  closely  the  natural  gum;  inasmuch  as  the  wax 
does  not  usually  hold  the  teeth  quite  close  to  the  model,  and  since  there  is 
tendency  for  the  teeth  to  move  out  slightly  during  soldering,  teeth  fitted 
to  a  model  thus  carved  will  fit  in  the  mouth  more  satisfactorily  than  if  it 
were  not  done.  The  teeth  are  now  fitted  to  the  model  without  the  plate 
sufficiently  to  determine  accurately  the  position  they  should  occupy. 
This  done,  cut  away  the  plate  nearly,  but  not  quite  as  much  as  will  be 


600  SWAGED  METALLIC  PLATES. 

re(iuirc(l,  miuI  iiftcr  hcNoliiii;-  the  e(l<,^(',  make  the  ed^e  fit  \ery  close  to  the 
model,  e\en  sinkiiit;-  it  slij^ditly  into  the  ])laster,  and  proceed  to  fit  the 
teeth  in  position  with  the  j)late  in  place.  As  the  work  proceeds  more  mav 
l)e  remoxed  from  the  plate  as  it  is  seen  to  be  necessary.  \\\  thns  proceed- 
ing, and  by  carefully  fitting  the  teeth  to  the  plate,  nsing  for  this  ])nrj)ose 
very  small  grindstones,  the  teeth  will  he  well  supported  by  the  plate, 
and  the  joint  between  the  plate  and  the  artificial  gum,  after  the  edge  of 
the  plate  has  been  burnislunl  close  to  the  porcelain  will  be  cleanly, 
smooth,  and  uon-irritating  to  the  tissues  against  which  it  will  rest  when 
the  finished  denture  is  in  use. 

Cases  are  met  with  where  an  artificial  gum  is  recjnired  on  account  of 
resorption  of  the  alveolar  l)order,  and  where  the  upper  lip  is  so  short 
that  the  edge  of  the  plate  is  lia})le  to  show  above  the  gums  of  the  teeth. 
In  these  cases  the  plate  is  cut  away  so  that  the  gums  of  the  artificial 
teeth  w'ill  just  cover  it,  and  the  teeth  are  so  fitted  that  the  edges  of  their 
gums  rest  upon  the  natural  gums.  In  such  cases  the  edge  of  the 
plate  is  not  beveled,  })ut  made  sciuare.  The  plate  is  cut  aAvay  only 
sufficiently  to  allow  the  artificial  gum  to  extend  from  one-sixteenth 
to  one-eighth  of  an  inch  beyond,  a  groove  is  then  cut  in  the  model  just 
beyond  the  plate-line  a  full  thirty-second  of  an  inch  deep,  as  far  as  the 
artificial  gum  is  to  rest  upon  the  natural  gum.  This  facilitates  an 
accurate  fitting  of  the  artificial  gum  to  the  edge  of  the  plate,  and  en- 
sures a  close  fit  of  the  artificial  gum  to  the  natural  gum.  If  too  much 
is  removed  from  the  model,  and  in  consequence  when  the  denture  is 
finished  the  artificial  gum  presses  too  hard  upon  the  natural  gum,  this 
is  readily  corrected  by  the  careful  use  of  a  small  grind-stone,  whereas 
if  it  does  not  fit  clorely  enough  the  fault  is  without  remedy. 

Plain  Teeth. — Plain  teeth  are  more  readily  arranged  than  gum  teeth. 
Where  conditions  favor  them,  they  make  a  stronger  and  more  cleanly 
denture.  It  is  exceptional,  however,  when  they  can  be  used  on  a  den- 
ture where  the  plate  extends  over  the  alveolar  border.  Cases  are  now  and 
again,  met  with,  however,  where  the  lips  are  long  and  the  tips  of  the  teeth 
are  alone  seen,  and  where  the  teeth  themselves  will  impart  sufficient  ful- 
ness; in  these  plain  teeth  may  be  used  with  decided  advantage.  The 
differences  in  the  technique  of  their  arrangement  from  that  of  gum  teeth 
in  full,  and  in  full  upper  and  lower  dentures  is  self-suggestive.  It  is 
quite  as  important,  and  the  same  care  is  required,  although  less  labor 
is  involved,  to  make  them  fit  accurately  to  the  plate  on  acount  of  cleanli- 
ness and  strength. 

Plain  teeth  are  especially  called  for  when  a  denture  is  made  soon  after 
natural  teeth  have  been  extracted,  or  where  the  alveolar  border  is  broad 
and  the  teeth  are  set  upon  or  into  the  natural  gum.  In  some  cases  the 
four,  six,  or  eight,  anterior  teeth  are  so  set,  the  teeth  further  back  being 
set  upon  the  plate;  in  some  cases,  indeed,  on  account  of  resorption  of 
the  posterior  portion  of  the  alveolar  border,  plain  teeth  may  be  used  in 
front  and  gum  teeth  at  the  back.  The  decision  to  use  plain  teeth  set 
upon  the  natural  gum  for  the  front  portion  of  the  denture  is  usually 
reached  when  marking  out  the  plate  line,  and  the  plate  made  accord- 


ARRANGING  AND  FITTING   THE  TEETH.  601 

ingly.  It  should,  however,  be  made  to  extend  over  the  alveolar  border 
a  little  more  than  seems  necessary,  as,  until  the  teeth  are  partly  arran,o;ed 
it  is  impossible  to  know  exactly  where  it  should  end.  It  is  very  desir- 
able that  the  ])latc  should  extend  under  the  teeth  as  far  as  it  ma.\',  and 
yet  be  well  co^•ered.  In  order  to  ascertain  how  to  trim  the  plate,  first 
arrange  the  teeth  to  the  model  without  the  plate;  while  so  doing  carve  the 
model  so  that  the  teeth  will  press  hard  into  the  gum.  How  freely  this 
should  be  done  depends  very  much  upon  the  condition  of  the  gums 
themseh'es.  If  the  teeth  ha\'e  been  recently  extracted,  or  if  the  gums 
are  quite  soft  and  yielding,  the  model  may  be  carved  quite  freely;  if  on 
the  contrary  they  are  hard,  it  must  be  done  more  cautiously.  This 
however,  may  be  remembered;  the  gums  usually  yield  under  pressure, 
even  when  the  pressure  is  very  slight,  there  is  usually  a  shrinkage  of  the 
gum  tissue  shortly  after  a  denture  is  inserted.  When  first  inserted  a 
tooth  may  fit  upon  the  gum  quite  neatly;  a  few  weeks  later,  on  account 
of  this  shrinkage,  it  may  not  touch  the  gum  at  all.  If  the  pressure  is 
too  great  the  fault  is  quickly  remedied  by  a  touch  of  the  grind-stone. 
The  beauty  of  plain  teeth  adjusted  to  the  natural  gum  consists  in  so  ar- 
ranging them  that  they  appear  to  be  growing  out  of  the  gum.  Having 
determined  to  what  extent  the  teeth  should  press  into  the  natural  gum 
and  the  position  of  the  two  central  incisors,  form  a  groove  of  the  de- 
sired depth,  its  lingual  side  sloping  and  its  labial  side  quite  perpendicular, 
into  which  the  teeth  are  to  be  fitted.  This  groove  is  to  be  extended  as 
the  laterals,  canines,  etc.,  are  fitted  into  place.  A  groove  is  preferable 
to  bodily  cutting  out  a  seat  for  the  teeth,  as  it  readily  permits  a  sidewise 
change  of  position,  and  shows  at  all  times  how  far  the  teeth  extend  be- 
neath the  surface  of  the  model.  When  as  many  of  the  teeth  as  are  to  set 
upon  the  gum  are  in  place  and  cemented  upon  the  model,  with  a  fine 
needle-point  make  a  traced  line  upon  the  model  around  their  necks,  thus 
marking  the  exact  position  of  each  tooth.  Remove  the  teeth,  and  cut  the 
plate  so  that  the  edge  shall  be  about  one-sixteenth  of  an  inch  within  the 
line,  not  following  the  festoons,  however,  but  making  the  edge  straight 
and  well  beveled.  The  triangular  portion  of  plate  between  the  teeth 
can  be  readily  and  neatly  cut  away  with  a  fine  file  when  finishing 
the  case.  Then  replace  the  teeth,  grinding  them  to  fit  over  the  plate. 
Usually  the  last  tooth  of  the  series  resting  upon  the  natural  gum  will  be 
the  first  or  second  bicuspid,  depending  partly  upon  the  condition  of  the  al- 
veolar border  as  regards  resorption,  and  partly  upon  how  far  the  plate  is 
visible  at  the  angles  of  the  mcuth.  As  a  rule  this  last  tooth  rests  partly 
upon  the  gum  and  partly  upon  the  plate;  it  should  be  so  set  as  to 
hide  as  much  as  possible  of  the  plate  beyond  it.  In  grinding  plain  teeth 
a  much  smaller  stone  is  required  than  for  grinding  gum  teeth. 

Plain  teeth  are  more  Hable  to  be  displaced  when  trying  them  in  the 
mouth  than  are  gum  teeth;  on  that  account  they  should  be  more  care- 
fully cemented  to  the  plate. 

The  technique  of  fitting  teeth  of  partial  soldered  dentures  differs  but 
slightly  from  that  of  fitting  teeth  of  any  form  of  partial  dentures  beyond 
the  fact  that  in  one  case  the  plate  is  fitted  to  the  teeth  after  the  teeth  have 


602 


SWAGED  METALLIC  PLATES. 


Fig.  549 


Fig.  550 


Lingual  aspect 
of  a  f  aul  t  y 
gum- joint,  in 
contact  on  the 
labial  side 
only. 


Lingual  aspect 
of  a  properly 
mad  e  g  u  m  - 
joint  between 
two  upper 
central  teeth, 
in  contact 
throughout. 


been  fitted  into  place,  antl  in  the  other  they  are  themselves  fitted  to  the 
plate.  Further  than  this  the  mechanical  and  artistic  requirements  are 
verv  much  the  same,  and  are  elsewhere  in  this  work  given  in  detail. 

General  Suggestions, — Corundum,  or  carborundum  wheels  of  coarse 
grit,  three-sixteenths  of  an  inch  thick  by  one  and  one-fourth  inch  in  diam- 
eter, having  a  round  edge,  are  used  for  the  rough  grinding.  For  the  final 
grinding  smaller  wheels  of  a  finer  grit  are  re- 
quired. For  joining,  some  prefer  a  ratherlarge 
wheel,  and  use  the  side  instead  of  the  edge ;  oth- 
ers a  wheel  about  one  and  one-half  inch  in  di- 
ameter, and  about  one-fourth  of  an  inch  thick, 
of  fine  grit,  and  with  a  square  edge,  kept  especi- 
ally for  this  purpose,  and  use  it  by  holding  the 
tooth  between  the  thumbs  and  index  fingers 
of  both  hands,  pass  the  joint  rapidly  across 
the'edge  of  the  wheel  backward  and  forward. 
It  is  best  to  be  provided  with  wheels  suitably 
for  side  or  edge  use,  and  not  to  confine  one's 
self  to  either  method,  but  to  practice  both.  It 
is  very  important  to  make  the  joints  in  such  a  manner  that  the  joint 
surfaces  are  in  contact  throughout,  as  shown  in  Fig.  550.  Great  care 
must  be  exercised  that  there  be  no  ^'-shaped  space  at  the  back  of  the 
joint  (Fig.  549) :  not  only  is  such  a  faulty  joint  uncleanly,  but  with  close 
contact  of  the  pink  borders  anteriorly  the  gum  will  almost  inevitably 
flake  when  the  teeth  expand  by  heat  during  the  process  of  soldering. 
The  bases  of  all  the  teeth  should  rest  solidly  upon  the  plate  (Fig.  551, 
A),  thus  bringing  the  strain  upon  the  bodies  of  the  teeth,  and  not  upon 
the  pins  (Fig.  551,  B),  as  occurs  when  the  teeth  are  imperfectly  fitted. 

When  fitting  teeth  to  the  natural  gum  it  is  well  to  remem})er  that 
this  portion  of  the  model,  especially  the  labial  surface  of  the  gum  and 
that  portion  immediately  adjoining  the  remaining  natural  teeth,  is  apt 
to  be  reproduced  a  trifle  larger  on  the  model  than  it  is  in  the  mouth,  even 
though  the  model  is  from  an  otherwise  faultless  impression.  This  may 
be  due  to  "creeping,"  when  wax,  or  the  so-called  "impression  com- 
pounds" are  used,  that  is,  a  slight  change  of  form  after  the  impression 
has  been  pressed  into  place  and  before  the  material  has  been  chilled 
sufficiently  to  make  its  form  permanent.  AYhen  plaster  is  used,  it  may 
be  due  to  the  sluggish  manner  in  which  the  plaster  flows  through  the 
interspaces,  or  to  neglect  in  pressing  the  plaster  to  the  gum,  or  the 
plaster  may  be  drawn  away  from  the  gums  by  the  lips  before  it  has  set, 
or  in  removing  the  impression  this  portion  may  break  in  such  a  manner 
as  to  prevent  accurate  replacement.  The  defect  frequently  occurs,  and 
while  it  is  generally  slight,  it  is  sufficient  to  make  a  decided  misfit  be- 
tween the  natural  and  artificial  gum.  This  may  be  corrected  by  carv- 
ing this  portion  of  the  model  before  fitting  the  teeth. 

Accurate  adjustment  of  the  teeth  to  the  plate  may  in  many  cases  be 
facilitated,  especially  in  partial  cases  and  with  teeth  that  stand  alone 
by  flattening  the  surface  of  the  plate  upon  which  the  teeth  rest  with  a 


TRYING  THE  TEETH  IN  THE  MOUTH. 


603 


flat  file;  the  amount  removed  may  be  trifling,  and  yet  it  may  make  a 
surface  much  easier  to  fit. 

Pigments  of  various  kinds  have  been  suggested  to  indicate  the  point 
of  contact  between  a  tooth,  and  the  plate  or  cast,  which  must  be  ground 
away  in  adjusting  a  tooth  m  position.  Thin  carbon  paper  cut  so  as  to 
lay  evenly  against  the  plate,  has  been  recom- 
mended; the  tooth  pressed  against  this  will  be 
marked  at  the  point  of  contact.  Rouge,  made 
into  a  paste  with  oil;  a  black  or  blue  crayon, 
or  a  blue  pencil,  may  be  used  to  color  the  sur- 
face against  which  the  tooth  is  to  fit.  They  may 
be  helpful  to  some;  a  skilled  workman,  how- 
ever, seldom  makes  use  of  them.  A  cultivated 
sense  of  touch  enables  one  to  know  with 
remarkable  accuracy  the  exact  point  to  which 
the  grind-stone  should  be  applied.  A  slight 
rubbing  motion  makes  a  white  spot  upon  the 
tooth  where  it  touches  the  plaster,  and  a  dis- 
tinctly discernible  mark  where  it  impinges  upon 
either  gold  or  silver,  provided  the  metal  is  not 
coated  with  wax.  These  marks  will  continue 
to  be  made.  Pigments  must  be  constantly  re- 
newed or  they  are  deceptive,  and  most  of  them 
are  unpleasant  to  use,  they  smear  and  soil  the  work  and  the  workman's 
hands. 


A.  A  gum  tooth,  accurately- 
fitted  to,  and  resting  upon  the 
plate 

B.  A  gum  tooth  imperfectly 
fitted  to  the  plate. 


TRYING  THE  TEETH  IN  THE  MOUTH. 


In  full  upper  or  lower  or  entire  dentures  the  points  to  be  carefully 
considered  when  trying  the  teeth  in  the  mouth  are — first,  the  accuracy 
of  the  articulating  model ;  if  that  is  correct  the  teeth  should  articulate  in 
the  mouth  very  nearly  as  they  do  upon  it;  second,  whether  the  joint 
between  tne  central  incisors  is  in  an  imaginary  line  bisecting  the  face; 
third,  whether  they  are  of  a  proper  length,  and  in  the  case  of  an  entire 
denture,  whether  the  relative  length  of  the  upper  and  lower  teeth  is  as 
it  should  be;  fourth,  whether  they  have  the  proper  slant  and  relative 
length,  one  with  the  other;  the  upper  teeth  should  slant  toward  the 
mesial  line,  and  in  a  young  person  the  centrals  should  be  a  trifle  longer 
than  the  laterals,  for  persons  advanced  in  age,  the  length  of  all  the  in- 
cisors should  be  the  same ;  the  lower  incisor  teeth  should  be  of  the  same 
length,  and  slant  but  little  if  at  all;  fifth,  the  fulness,  that  is,  whether 
the  normal  lip  outline  is  restored;  and  sixth,  the  expression  and  the 
changes  in  expression  and  in  articulation  due  to  the  movements  of  the 
mouth  and  adjacent  parts,   and  their  general  harmony. 

Inasmuch  as  nearly  all  changes  in  soldered  plate  work  must  be  made 
with  the  grind  stone,  and  that  any  portion  of  a  tooth  once  removed 
cannot  be  restored,  it  is  a  wise  precaution  when  constructing  full,  or 


604  SWAGED  METALLIC  PLATES. 

nearly  full  (U'liturcs,  to  make  a  j)reliiniiiary  trial  of  the  teeth  in  the 
mouth  when  they  are  partly  arranged.  It  is  a  satisfaction  to  know  that 
the  models  are  correct,  and  to  have  a  i;eneral  idea  of  how  the  teeth 
should  he  when  accurately  adjustinjj;  them  to  jjosition.  Trifiinj;-  changes 
in  the  articulation  noted  us  needed  when  trying  the  teeth  in  the  mouth, 
chanf^es  that  it  is  seen  can  l)e  readily  made  with  the  i-rindstone,  may 
be  left  until  the  denture  is  finished;  some  changes  that  may  seem  neces- 
sary at  this  time  may  not  be  needed  when  the  patient  can  close  the 
mouth  firmly  without  danger  of  disi)lacing  the  teeth  from  the  plate. 

If  the  articulating  model  is  correct,  required  changes  in  length,  slant, 
or  fulness  may  be  indicated  l)y  moving  the  teeth  concerned  into  new 
positions  until  the  desired  effect  is  produced,  making  no  attempt,  how- 
ever, to  refit  them  until  a  satisfactory  rearrangement  has  been  effected. 
If  these  changes  are  at  all  extensive,  it  is  best  to  try  the  denture  again 
in  the  mouth  after  they  have  been  made. 

If  the  articulating  model  should  prove  defective,  or  the  teeth  be  found 
too  long  or  too  short,  it  is  better  to  place  a  little  soft  wax  between  the 
teeth  on  each  side  of  an  entire  denture  or  all  around  an  upper  or  lower 
denture,  and  proceed  to  take  a  new  articulation,  allowing  the  teeth  to 
remain  upon  the  plate  if  they  do  not  interfere,  as  their  presence  aids  in 
the  correction  of  the  defects  of  the  old  articulation.  ]\Iake  also  a  new 
articulating  model:  this  course  is  far  more  satisfactory  than  to  attempt 
to  alter  the  old  one,  and  saves  time  in  the  end. 

Trying  partial  cases  in  the  mouth  is  frecjuently  a  difficult  task,  es- 
pecially if  the  teeth  are  scattered.  If  a  hard  cement  is  used,  it  is  nec- 
essarily brittle,  and  the  teeth  are  broken  from  the  plate  with  the  slight- 
est strain;  if  the  cement  is  soft,  they  will  move,  and  unless  carefully 
watched  and  their  position  in  the  mouth  compared  with  their  position 
u})on  the  model,  the  tr\ing  in  will  amount  to  but  little.  Quite  fre- 
cjuently  the  teeth  fit  so  tightly  between  the  remaining  natural  teeth,  or  are 
placed  at  such  an  angle,  that  the  plate  cannot  be  removed  from  the 
mouth  without  displacing  them.  In  these  cases  endeavor  to  judge  what 
changes  are  necessary  and  adjust  the  teeth  to  the  model  after  the  plate 
is  removed  from  the  mouth.  It  is  not  always  desirable  to  arrange  the 
teeth  so  that  they  can  be  readily  placed  in  the  mouth  while  fastened  on 
the  plate  with  cement;  it  may  be  a  decided  advantage  to  make  them  fit 
too  tightly  for  this.  Or,  again,  the  natural  teeth  may  so  lean  that,  although 
it  is  quite  difficult  to  pass  over  them  the  plate  with  the  teeth  attached 
with  cement,  the  finished  case,  with  the  teeth  and  plate  firmly  united 
with  solder,  will  readily  spring  into  place,  and  be  held  more  securely 
and  comfortably  than  if  made  to  go  into  place  easily.  A  well  fitting 
partial  denture  may  have  to  be  manneuvered  into  place,  one  side  being 
inserted  first,  or  be  twisted  and  turned  to  accomodate  leaning  or  mis- 
placed teeth,  or  it  may  require  a  little  force  to  press  it  into  position. 
This  can  seldom  be  done  with  the  teeth  secured  to  the  plate  with  ad- 
hesive wax.  In  these  cases  the  main  purpose  of  trying  in  the  teeth 
is  to  discover  and  correct  inaccuracies  of  the  model,  to  see  that  the  teeth 
in  size,  shade,  and   character   harmonize  with  the  natural  teeth,  and 


RIMMING.  605 

that  the  artificial  teeth  are  in  a  position  where  they  can  be  made  to 
fill  properly  the  spaces  when  they  are  firmly  soldered  to  the  plate. 
Cases  now  and  again  occur  where,  when  the  teeth  are  in  their  proper 
position,  it  is  impossible  to  remove  them  and  the  plate  from  the  model, 
and  it  becomes  necessary  to  break  off  one  or  more  of  the  plaster  teeth 
in  order  to  remove  the  case  from  the  model  without  displacing  them. 
It  has  been  suggested  that  a  case  which  cannot  be  removed  from  the 
model  without  mutilating  it  cannot  be  inserted  in  the  mouth;  it  must  be 
remembered  that  the  plaster  teeth  of  the  model  are  very  much  more  rigid 
than  are  the  natural  teeth  in  the  mouth,  and  that  they  are  not  al- 
ways accurate  in  shape.  Such  a  case  may  require  more  or  less  "fitting," 
when  it  is  finally  inserted  after  finishing,  but  will,  as  a  rule,  prove  more 
satisfactory  fitted  to  the  mouth  than  if  it  had  been  fitted  to  the  model. 
^Vlien  satisfied  with  the  arrangement  of  the  teeth,  before  investing, 
see  that  they  hold  in  place  sufficiently  firm  that  they  will  not  be  displaced 
when  pressed  into  the  investment.  Teeth  standing  alone  may  require 
for  additional  security,  a  drop  of  wax  underneath,  at  the  point  where  the 
plate  and  porcelain  meet;  a  little  soft  wax  flowed  inside  long  and  w^eak 
gums  may  ward  off  an  accident  when  the  case  is  removed  from  the  in- 
vestment after  soldering. 

RIMMING. 

The  addition  of  a  rim  to  dentures  of  single  gum  or  block  teeth — that 
is,  a  band  of  gold  or  silver  upon  the  border  or  edge  of  either  an 
upper  or  lower  plate  to  receive  the  gum  extremities  of  the  teeth — adds 
very  much  to  the  strength  and  to  the  artistic  appearace  of  the  denture. 
It  can  be  added  only  when  the  plate  extends  beyond  the  gums  of  the 
teeth,  and  when  the  lip  is  sufficiently  long  to  prevent  its  being  seen  whei: 
the  mouth  is  widely  opened  and  the  lips  retracted,  as  in  laughing,  etc. 
Rims  are  not  confined  to  full  dentures;  they  may  be  applied  to  either 
upper  or  lower  partial  cases  where  there  are  a  number  of  single  gum  or 
block  teeth  together.  If  the  work  is  well  done,  rimming  makes  a  neat 
finish  to  the  denture  ;  the  thick,  smooth,  rounded  edge  is  more  comfort- 
able to  the  patient,  and  the  rim,  covering  the  joints  between  the  plate 
and  the  teeth  with  its  free  edge  burnished  closely  to  the  gum  extremities 
of  the  teeth  prevents  the  lodgement  of  food,  etc.,  and  thus  adds  very 
much  to  its  cleanliness.  Rimming  also  materially  strengthens  the  den- 
ture, not  only  by  the  amount  of  gold  or  silver  added  to  a  weak  part  of 
the  plate,  but  also  by  forming  a  groove  or  socket  in  which  the  ends  of 
the  teeth  rest,  protecting  them  from  injury  and  assisting  the  platinum 
pins  in  resisting  the  strain  of  mastication,  especially  those  of  the  molars 
and  bicuspids.  Rimming  a  plate  before  the  teeth  are  fitted  to  it  is  a 
very  simple  matter.  It  is  done  immediately  after  the  plate  has  been 
adjusted  to  the  mouth,  the  articulation  secured,  and  the  articulating 
cast  made.  The  wax  used  in  taking  the  articulation,  giving  also  the 
intended  fulness  of  the  gum,  indicates  the  width  of  the  rim.     In  locat- 


606 


SWAGED  METALLIC  PLATES. 


ing  the  position  of  the  rim  two  things  are  to  be  considered :  first,  the 
probabiHty  of  the  border  of  the  plate  extending  too  far  over  the  alve- 
olar ridge;  and  second,  the  probability  of  the  rim  being  seen  when  the 
mouth  is  widely  opened.  Provision  must  be  made  for  reducing  the  size 
of  the  plate  without  injury  to  the  rim  should  its  border  press  too  firmly 
upon  the  soft  tissues.  To  this  end  the  rim  is  located  a  little  inside  the 
outer  border  of  the  plate,  but  not  so  far  as  to  be  exposed  in  laughing, 
etc. ;  and  in  soldering  it  to  the  plate  the  solder  is  allowed  to  run  into  and 
fill  the  apex  of  the  angle  between  the  rim  and  the  plate.  In  construct- 
ing such  a  rim  take  a  strip  of  plate  sufficiently  long,  about  No.  26  Amer- 
ican Standard  wire  gauge  (.01594  of  an  inch  thick,) — ^the  wadth  of 
the  intended  rim.  After  cleaning  the  plate,  adjust  the  strip  at  about 
the  middle  of  its  length  so  that  one  edge  touches  the  plate  at  its  median 
line  and  other  stands  out  from  it  at  an  acute  angle,  forming  a 
groove  or  socket  into  which  the  teeth  are  to  be  fitted.     This  may  be 


Fig.  5.52 


Method  of  tightening  wire  in  operation  of  "tying  down." 

held  in  place  for  soldering,  with  binding  wire,  with  a  wire  clamp,  or  it 
may  be  held  with  adhesive  wax  and  invested  for  soldering.  Begin 
soldering  by  "tacking  it" — that  is,  flowing  a  little  solder  so  as  to  unite 
the  rim  and  the  plate  a  portion  of  the  distance  they  have  been  fitted : 
the  object  is  to  unite  them  firmly  at  one  point,  so  as  to  facilitate  fitting 
the  remaining  portion  of  the  rim.  If  the  portion  of  rim  soldered  does 
not  form  a  desirable  angle  \f'ith  the  plate,  it  may  be  bent  with  the  pliers, 
in  or  out,  until  it  does.  Now  proceed  to  fit  the  strip  to  the  plate  as  far 
as  it  can  be  conveniently  done,  securing  it  in  position  with  binding 
wire,  and  .solder.  Repeat  this  until  the  rim  is  fitted  and  .soldered  nearly 
as  far  as  it  is  intended  to  go.  As  the  exact  po.sition  of  the  last  molar 
cannot  be  determined  at  this  stage,  an  ample  length  of  the  strip  is  left 
unsoldered,  enough  to  continue  the  rim  around  the  posterior  of  the 
last  molar.  This  is  to  be  fitted  and  soldered  after  the  teeth  are 
arranged  in  place.  The  rim  is  now  neatly  finished  by  being  reduced 
with  a  file  to  a  proper  width,  and  the  free  edge  slightly  beveled.     This 


RIMMING.  607 

method  of  forming  a  rim  may  be  used  on  either  an  upper  or  lower 
plate. 

Of  the  many  methods  which  have  been  from  time  to  time  suggested 
for  rimming  dentures  of  single  gum  teeth,  after  the  teeth  have  been 
fitted,  the  following  are  selected  as  being  simple  and  practicable. 

For  many  years  the  writer  invariably  rimmed  these  cases  after  the 
teeth  were  soldered  to  the  plate:  in  doing  so  there  is  a  slight  risk  of 
shattering  the  gums  during  soldering,  and  of  warping  the  plate,  but 
with  care  in  investing,  in  applying  the  borax,  and  in  soldering,  acci- 
dents seldom  occur.  It  is  done  quickly,  and  with  much  less  labor  than 
by  any  other  method;  a  rim  so  made  is  neat,  strong,  and  effective. 
When  this  method  is  followed,  after  the  case  is  soldered  and  cleaned 
by  acid,  and  before  commencing  to  finish  the  backings,  carefully  wash 
the  denture  to  remove  all  trace  of  acid,  and  then  grind  the  gum  ends  of 
the  teeth  until  they  conform  to  an  even  line  from  heel  to  heel  of  the 
plate,  removing  the  rounded  edge,  and  forming  an  even  bevel  of  a 
somewhat  obtuse  angle  to  receive  the  rim.  It  is  important  that  the 
finished  rim  should  fit  with  absolute  closeness  to  the  teeth  at  its  free 
edge;  and,  as  it  is  more  difficult  to  burnish  it  to  a  rounded  surface  than 
to  a  flat  one,  this  should  be  borne  in  mind  in  preparing  a  denture  for 
rimming. 

It  is  important  also  to  have  sufficient  room  between  the  ends  of  the 
teeth  and  the  edge  of  the  plate,  not  only  to  solder  the  rim,  but  also  to 
give  the  rim  sufficient  width  to  avoid  making  the  edge  too  abrupt. 

If  the  rim  is  narrow  and  of  the  same  width  from  end  to  end,  half- 
round  wire,  letting  the  flat  side  rest  against  the  teeth,  is  usually  to  be 
preferred;  if  wide,  or  wide  at  some  points  and  narrow  at  others,  it  is 
best  to  cut  a  paper  pattern  and  make  the  rim  of  plate  about  No.  24 
gauge  (.0201  of  an  inch  thick).  Usually  the  rim  of  a  low^er  denture  is 
made  in  one  piece,  that  for  an  upper  denture  is  sometimes  more  conven- 
iently made  in  two  pieces,  each  extending  from  the  mesial  line  to  the 
tuberosities  of  either  side,  overlapping  at  the  mesial  line  to  make  a 
neat  joint. 

When  preparing  to  solder  a  case  which  is  intended  to  be  rimmed  in 
this  manner,  a  piece  of  plate  should  be  fitted  around  the  back  part  of 
each  end  molar,  extending  from  the  backing  as  far  around  the  molar 
gum  as  it  can  be  soldered,  and  soldered  in  place  at  the  same  time  as  the 
teeth  are  soldered  to  the  plate.  This  is  intended  to  form  part  of  the 
rim,  and  is  fitted  and  soldered  at  this  time  on  account  of  the  difficulty  of 
reaching  that  part  when  the  case  is  invested  for  soldering  the  other 
portions  of  the  rim. 

The  method  of  fitting  the  rim  is  the  same  for  either  plate  or  half-rouud 
wire.  Begin  at  the  median  line,  and  carefully  bend  the  plate  or  half- 
round  wire  with  either  the  fingers  or  pliers  until  it  fits  accurately  in 
place,  bevehng  each  end  so  as  to  make  a  neat  joint  with  the  piece  ex- 
tending from  the  backings  around  the  last  molar  at  one  end,  or  if  made 
in  two  parts,  with  the  other  half  of  the  rim  at  the  median  line.  It  is 
hardly   probable  that  it   can  be  fitted  so  accurately  when  invested  in 


(306  SWAGED  METALLIC  PLATES. 

})lace  as  not  to  sprin<^  somewhat,  hut  it  sliould  so  lu'nrly  fit  that  the 
iron  hiiKhng  wire  used  to  hokl  it  in  position  (hiring  sohlering  simply 
hohls  it  in  place,  and  is  not  depended  upon  to  draw  it  close  to  the 
teeth.  If  the  fitting  is  imperfectly  done  and  the  rim  is  drawn  close  to 
the  teeth  by  the  wire,  it  may  seem  to  fit  accurately  when  invested; 
but  when  the  case  is  heated  for  soldering,  the  binding  wire,  becoming 
hot  before  the  rim,  will  expand  and  allow  the  rim  to  spring  from  the 
teeth,  so  that  after  it  is  soldered  it  will  be  a  difficult,  if  not  an  impossible 
task  to  bend  or  l)urnish  it  to  fit  as  closely  to  the  teeth  as  it  should. 
fVfter  the  rim  is  fitted  as  accurately  as  possible,  it  may  be  held  in  place 
for  investing  with  adhesive  wax,  or  preferably  with  iron  binding  wire. 
For  this  purpose  annealed  iron  wire  No.  30  or  32  may  be  used;  strength 
is  of  small  importance;  there  should  be  but  little  strain  upon  it.  Before 
placing  the  rim  in  position,  paint  the  porcelain  against  which  it  is  to 
rest  with  a  thin  coating  of  whiting  and  water  or  plaster  and  water,  let- 
ting it  run  in  between  the  gums  of  the  teeth  and  the  plate,  but  carefully 
keeping  it  from  any  part  upon  which  the  solder  is  intended  to  flow.  This 
is  mainly  to  prevent  the  borax  from  coming  in  contact  with  the  porce- 
lain. 

Adjust  the  rim  in  place,  and  pass  a  wire  around  the  case  in  such  a 
position  as  to  impinge  upon  the  rim  on  both  sides — say  between 
the  bicuspids  or  the  bicuspid  and  molar — passing  it  between  the  teeth 
or  over  the  occlusal  surface  as  may  be  most  convenient;  twisting  the 
ends  together  so  as  barely  to  draw  it  tight  enough  to  hold  the  rim 
in  place;  then,  taking  hold  of  the  wire  with  the  flat  pliers,  draw 
it  sufficiently  tight  by  bending  it  upon  itself.  If  the  tightening  is 
done  entirely  by  twisting  the  ends,  there  is  a  great  risk  of  changing 
the  shape  of  the  plate  either  while  placing  the  wires  in  position  or 
during  soldering;  by  bending  the  wires  as  suggested  sufficient  strain 
is  exerted  to  hold  the  rim  securely,  without  the  slighest  risk  of  bend- 
ing the  plate;  the  wire,  so  bent,  is  not  a  rigid  band  around  the  case, 
but  exerts  an  elastic  pressure.  Place  as  many  wires  around  the  case, 
in  any  direction  most  convenient,  as  may  be  necessary  to  hold  the  rim 
securely.  If  half-round  wire  is  used  for  the  rim,  it  should  be  wide 
enough  on  the  flat  side  to  reach  from  the  plate  sufficiently  far  over  the 
gums  of  the  teeth  to  cover  the  bevel  made  with  the  grindstone,  but 
not  to  extend  beyond  this.  Where  it  passes  over  slight  depressions 
in  the  plate,  do  not  bend  the  wire  to  fit  them,  but  depend  upon  fitting 
a  piece  of  plate  to  fill  the  vacancy. 

Wlien  the  rim  is  accurately  adjusted  and  held  in  place  with  adhesive 
waxor  with  wire,  proceed  to  invest  the  case  for  soldering,  using  for  this 
purpose  a  mixture  of  plaster  and  sand  precisely  the  same  as  is  used  for 
investing  to  solder  the  teeth  to  the  plate.  First  fill  the  lingual  surface  of 
the  denture  with  the  investing  material  to  a  level  with  the  tops  of  the  teeth 
then  invert  it  over  a  massof  investment  previously  placed  upon  a  piece  of 
glass,  pressing  it  down  so  as  to  leave  about  one-quarter  of  an  inch  under 
the  cutting  edges  of  the  teeth;  then  build  it  up  outside  of  the  teeth  about 
one-half  of  an  inch  thick,  high  enough  to  protect  thoroughly  the  gums  and 


RIMMING  609 

to  extend  a  trifle  over  the  free  edge  of  the  rim:  build  the  batter  up  quite 
wide  at  the  top,  so  that  there  will  be  no  danger  of  its  cracking,  so  as  to 
expose  the  gums  of  the  teeth.  Build  it  up  at  the  back  part  so  that  the 
posterior  edge  of  the  plate  is  well  covered,  and  extend  it  over  the 
palatal  surface  to  a  little  beyond  the  margin  of  the  vacuum-cavity,  so 
shaping  it,  however,  so  as  to  permit  soldering  the  rim  far  enough 
around  the  last  molar  of  each  side  to  meet  the  piece  extending  from 
the  backings. 

When  the  investment  has  set  proceed  to  solder  the  rim.  If  binding 
wire  has  been  used,  do  not  disturb  it.  Apply  borax  carefully  and  not 
too  freely,  add  sufficient  solder  to  "tack"  the  rim  at  a  number  of  points, 
and  proceed  to  heat  the  case  preparatory  to  soldering.  When  using 
the  blowpipe  to  flow  the  solder,  avoid  directing  the  pointed  flame  against 
that  part  of  the  plate  immediately  back  of  the  gums  of  the  teeth.  En- 
deavor to  heat  the  case  evenly,  and  after  fixing  the  rim  in  position  by  fus- 
ing or  flowing  the  solder  first  placed,  cut  or  break  those  strands  of  bind- 
ing wire  not  fused  or  burned  in  two,  and  carefully  bend  their  ends  out 
of  the  way,  taking  especial  care  not  to  disturb  the  investment.  Any  por- 
tions of  binding  wire  held  by  the  solder  or  borax,  and  not  readily 
removable,  may  be  allowed  to  rest  until  completing  the  soldering 
when,  if  in  the  way,  it  may  be  pushed  aside  with  the  soldering-point. 
Then  begin  at  one  end  of  the  rim  and  reflow  the  solder,  adding  enough 
more  to  fill  the  sharp  angle  between  the  rim  and  the  plate  and  to  permit 
a  smooth,  neat  finish. 

This  method  of  rimming  is  more  rapid  than  any  other,  and  has  the 
decided  advantage  that  after  the  teeth  have  been  adjusted  to  the  mouth 
and  finally  fitted  they  are  not  again  removed  from  the  plate.  It  re- 
quires careful  attention  to  detail  to  avoid  fracturing  the  teeth  or  warp- 
ing the  plate,  but  in  careful  hands  it  is  by  no  means  as  hazardous  as 
might  be  supposed.  The  description  refers  to  a  full  upper  denture, 
but  the  method  may  be  used  equally  well  for  rimming  partial  or  lower 
dentures,  the  changes  needed  when  it  is  a  applied  to  these  will  readily 
suggest  themselves. 

To  rim  a  denture  after  the  teeth  have  been  finally  fitted  to  the  plate 
and  before  they  are  soldered  in  position,  proceed  as  follows : — 

Place  the  denture  fully  prepared  for  investing  upon  the  plaster  model, 
having  previously  made  one  or  more  cone-shaped  holes,  or  a  vertical 
groove,  in  the  back  part  to  serve  as  guides  to  readjust  to  the  model  the 
model  now  to  be  made;  and  after  varnishing  the  surface  of  the  model  so 
that  plaster  now  to  be  added  will  not  unite  with  it,  proceed  to  build 
plaster  upon  the  model  precisely  as  though  making  an  articulating  model, 
allowing  it  to  extend  above  the  teeth  and  just  to  the  outer  edge  of  their 
occlusal  surface  and  over  the  back  part  of  the  model,  so  as  to  have  a  solid 
bearing.  When  this  is  hard,  smooth  the  edge  immediately  over  the  teeth, 
making  around  it  a  number  of  cone-shaped  pits,  and  after  properly  pre- 
paring the  surface  of  the  plaster  to  prevent  union,  add  plaster  so  as  to  ex- 
tend over  the  surface  of  the  teeth  as  far  as  the  gums,  and  to  extend  over 
the  plaster  model  previously  made  sufiiciently  far  to  give  it  a  soHd  bear- 

39 


610 


SWAGED  METALLIC  PLATES. 


iiifj-  (Fig.  553.)  The  object  is  to  imbed  the  teeth  thoroughly  in  plaster,  so 
that  in  fitting  the  rim  they  can  be  removed  from  the  plate,  and  readjusted 
as  though  they  were  one  piece.  This  guide  is  made  in  two  sections,  so 
that  if  desired  when  the  rim  is  finished  the  last-made  section  may  be  re- 
moved without  disturbing  the  relation  of  the  teeth,  to  permit  of  the  den- 
ture being  invested  in  the  manner  presently  to  be  described.  This 
plaster,  v.hen  set,  will  hold  the  teeth  securely  and  the  denture  may  be 
removed  from  the  cast  and  the  gum  ends  of  the  teeth  ground  even  and 


RiG.  5oa 


Guide  to  hold  single  gum  teeth  together  whUe  adjusting  a  rim,  a  portion  broken  away  to 
ghow  its  construction.  This  guide  is  made  in  two  parts,  the  first  rests  upon  the  cast  and  fills  the 
inner  portioa  of  the  denture,  extending  over  the  teeth  and  just  to  the  outer  edge  of  their 
occlusal  surface.  The  second  part  fits  onto  the  first  part,  and  extends  over  the  teeth  to  near 
the  extreme  ends  of  their  gums.  The  two  parts  hold  the  teeth  together  so  that  they  can  be 
removed  from  the  plate  and  handled  during  the  fitting  of  the  rim  as  one  body;  they  are  not 
separated  until  the  rim  is  quite  finished  and  the  denture  ready  to  be  invested  for  solderin?. 


to  a  bevel  precisely  as  described  for  rimming  after  soldering  the  teeth  to 
the  plate. 

The  rim  may  be  fitted  to  the  teeth  by  swaging,  making  the  die  for  each 
half  of  the  rim  by  molding  in  sand  directly  from  the  denture;  or  by 
taking  a  plaster  impression  of  the  parts  to  which  the  rim  is  to  be  fitted, 
and  from  this  making  a  plaster  model  to  be  reproduced  in  zinc  by  the 
usual  method;  or  by  taking  this  impression  in  a  mixture  of  molding  sand 
and  plaster  or  other  impression  material  into  which  zinc  can  be  cast. 
After  the  zinc  die  is  made  a  lead  counter-die  is  obtained  in  the  usual 
manner.  Then,  cut  a  paper  pattern  by  which  to  cut  the  metal  strip  of 
which  the  rim  is  to  be  made.  Swaged  rims  should  be  made  to  extend 
to  the  border  of  the  plate;  thus  made,  they  are  much  easier  to  swage  and 
to  solder  and  make  a  neater  finish.    There  is  usually  a  little  diflBculty  in 


RIMMING.  611 

holding  the  strip  in  place  upon  the  die  when  commencing  to  swage,  and 
a  constant  liabiUty  of  its  moving  out  of  position  during  that  operation 
unless  great  care  is  used. 

After  the  rim  is  swaged  and  fitted  to  its  position,  the  two  halves  being 
slightly  beveled  and  overiapping  at  the  median  line,  so  as  to  make  a 
neat  joint,  and  that  part  extending  around  the  last  molar  of  such  side 
adapted  to  make  a  continuous  band  to  and  uniting  with  the  backings, 
it  may  be  held  in  place  for  investing  by  shellac,  or  by  a  little  plaster 
-  placed  at  several  points,  or  by  drilling  several  rivet  holes  and  riveting  it 
in  place.  This  latter  method  is  by  far  the  most  secure  and  is  readily 
done  if  there  is  room  between  the  gums  and  the  edge  of  the  plate  for 
the  rivets.  The  rivets  are  to  be  placed  in  the  holes  and  tightened  before 
the  teeth  are  removed  from  the  plate,  so  that  there  will  be  no  risk  of  the 
rim  changing  its  position  during  investment  and  soldering.  Then 
slightly  warm  the  plate  by  holding  it  over  a  Bunsen  burner  or  a  spirit 
lamp  and  remove  the  plate,  leaving  the  teeth  imbedded  in  the  plaster 
molds.  The  plate  and  rim  are  removed  from  the  teeth  for  investment  in 
the  same  way  if  the  rim  is  held  by  shellac  or  plaster :  it  must  be  done, 
however,  very  carefully. 

The  plate  with  the  rim  is  now  invested  in  a  mixture  of  plaster  and 
sand  such  as  is  used  for  investing  teeth.  If  the  rim  is  very  narrow 
and  does  not  extend  much  over  the  plate  above  the  teeth,  it  should  be, 
before  investing,  painted  on  the  inside  with  whiting  or  plaster  to  keep 
the  solder  from  filling  it  up;  in  other  cases,  it  is  better  that  the  solder 
should  run  in  slightly,  so  that  there  will  be  no  danger  of  filing  through  if 
it  should  be  found  necessary  to  reduce  the  size  of  the  plate:  a  little  care 
in  soldering  will  prevent  the  solder  filling  the  socket  so  as  to  interfere 
with  the  teeth. 

By  a  second  method,  place  the  denture  fully  prepared  for  the  re- 
ception of  the  rim  on  the  model  and  proceed  to  make  a  plaster  impression 
of  the  parts  to  which  the  rim  is  to  be  fitted,  allowing  the  impression  to 
extend  around  the  last  molar  as  far  as  the  rim  is  to  go,  and  to  rest  upon 
the  front  part  of  the  model  sufiiciently  to  permit  of  its  removal  and  accu- 
rate replacement,  the  model  having  been  previously  prepared  to  prevent 
the  new  plaster  from  uniting  with  the  old.  When  the  impression  has 
set,  remove  it  by  inserting  a  thin  knife-blade  between  the  new  and  old 
plaster;  it  is  seldom  that  its  shape  wdll  permit  its  removal  in  one  piece, 
but  with  a  little  care  it  can  generally  be  broken  away  in  but  few  pieces. 
Then  remove  the  denture,  and  after  warming  the  plate  remove  it,  leav- 
ing the  teeth  imbedded  in  the  guides.  Clean  the  adherent  wax  from 
the  plate,  and  after  replacing  it  upon  the  model  replace  the  impres- 
sion, securing  it  in  position  with  adhesive  wax;  oil,  or  otherwise  pre- 
pare the  impression  so  that  new  plaster  will  not  unite  with  it,  and  pro- 
ceed to  run  plaster  mixed  with  pumice  stone  or  marble  dust  so  as  to 
be  non-shrinking  when  heated  into  it,  in  order  to  secure  a  fac-simile  of 
that  part  of  the  teeth  to  which  the  rim  is  to  be  fitted,  allowing  the 
plaster  to  extend  over  the  lingual  surface  of  the  plate  so  as  to  give  the 
cast  sufficient  strength.     Any  of  the  prepared  investment  materials 


612  Sn'AUJW  METALLIC  PLATES. 

may  l)e  used  in  place  of  plaster.  When  this  has  set,  remove  the  im- 
j)ressi()n.  Now  proceed  to  adjust  a  rim  to  this  fac-simile  of  the  teeth 
in  precisely  the  same  manner  as  though  it  was  the  teeth  soldered  to  the 
plate,  holding  it  in  place  with  binding  wire  precisely  as  directed  when 
describing  that  method,  taking  especial  care,  however,  not  to  draw  the 
wire  so  tightly  as  to  crush  the  plaster.  The  rim  is  soldered  without  in- 
vesting. Success  by  this  method  depends  upon  careful  mani])ulation, 
and  upon  securing  an  accurate  fac-simile  of  the  teeth  in  a  material  making 
a  smooth,  sharp  model,  and  one  not  readily  abraded,  and  that  does  not 
shrink  when  heated  to  the  fusing  point  of  the  solder  used. 

By  the  third  method  the  rim  is  fitted  to  the  teeth  themselves,  as  is  a 
swaged  rim,  and  held  in  place  with  shellac  or  plaster  while  the  teeth 
imbedded  in  the  mold  are  removed  from  the  plate.  The  plate  and  rim 
are  then  invested,  the  iuA'estment  being  molded  to  extend  slightly  over 
the  free  edge  of  the  rim  to  hold  it  in  place.  It  is  seldom  necessary  to 
place  whiting  or  plaster  inside  the  rim  to  keep  the  solder  from  entering; 
the  investment  usually  prevents  its  encroaching  upon  the  space  required 
for  the  teeth. 

The  writer  prefers  this  latter  method.  It  is  simple,  less  labor,  and  as 
the  rim  is  fitted  to  the  teeth,  errors  of  adaptation  owing  to  a  model  being 
abraded  or  broken  are  avoifled.  When  time  is  no  object,  and  the  work- 
man not  accustomed  to  fitting  rims,  or  for  special  cases,  swaging  gives 
good  results.  Theoretically,  it  should  give  more  accurate  results  than 
any  other  method,  but  practically  there  are  so  many  difficulties  en- 
countered in  constructing  the  dies,  in  keeping  the  strips  of  metal  be- 
tween them,  in  so  arranging  that  the  impact  of  the  blow  will  swage 
the  rim  evenly,  that  it  is  seldom  practised  by  practical  workmen. 

It  is  a  mistake  to  make  a  rim  of  very  thin  metal.  Gold  should  not 
be  less  than  No.  26,  while  silver  should  be  a  little  heavier.  The  thicker 
metal  holds  its  position  better  during  soldering;  its  free  edge  is  readily 
thinned  with  a  file  as  may  be  found  necessary  when  burnishing  it  close 
to  the  tooth  gums,  and  is  not  so  fiable  to  stretch  under  the  burnisher. 
Where  it  can  be  used,  half-round  wire  has  decided  advantages.  It  is 
readily  bent  in  any  direction,  and  has  thickness  where  thickness  is  most 
desirable;  it  requires,  however,  owing  to  its  rounded  edge,  the  free  use  of 
solder  or  the  addition  of  narrow  strips  of  plate  to  avoid  an  objectionable 
groove  at  its  junction  with  the  plate. 

The  investment  has  but  a  slight  hold  on  the  rim,  this  will  suggest 
care  in  preparing  for  soldering,  and  care  during  that  operation  to  pre- 
vent its  displacement.  It  is  usually  best  to  heat  up  invested  rims  slowly 
and  to  heat  them  as  hot  as  one  would  for  soldering  teeth;  otherwise 
when  the  hot  blowpipe-flame  strikes  the  narrow  rim  it  is  suddenly  ex- 
panded and  curves  up;  making  a  displacement  difficult  to  contend  with 
when  finishing  the  denture.  Care  shoidd  also  be  exercised  to  avoid 
fusing  the  rim,  an  accident  very  difficult  to  repair;  or  allowing  the  solder 
to  flow  over  it,  especially  near  its  free  edge.  Small  pieces  of  solder 
should  be  placed  at  intervals,  and  these  should  be  first  fused  tacking  the 
rim  to  the  plate  quickly.    This  accomplished,  begin  at  one  end  and  flow 


RIMMING.  613 

the  solder  in  sufficient  amount  to  make  a  joint  that  will  finish  up  neatly; 
where  much  filling  in  is  needed,  narrow  strips  of  i)late  may  be  added. 

After  the  rim  is  soldered  and  the  j^late  cleansed  with  acid,  place  it 
on  the  model  to  see  that  it  fits  as  accurately  as  it  did  before — it  is  seldom 
that  there  is  any  material  change  if  the  work  has  been  carefully  done; 
then  proceed  to  adjust  the  rim  and  to  finish  it  as  far  as  is  desirable  to  do 
before  the  case  is  invested. 

As  it  is  difficult  to  get  a  smooth,  even  edge  to  a  rim  after  the  teeth  are 
soldered  to  the  plate,  the  rim  edge  should  now  be  finished,  using  for  the 
purpose  a  dead-smooth  file  and  very  fine  emery  or  sand-paper.  Do 
not  bevel  the  edge  too  much;  it  should  be  rounded  rather  than  beveled 
from  the  labial  side,  and  left  thick;  it  will  be  somewhat  further  reduced 
when  it  is  burnished  close  to  the  teeth  in  finally  finishing  the  case,  and 
if  made  too  thin  it  is  apt  to  tear  and  break  during  that  operation. 

The  next  step  is  to  readjust  and  secure  the  teeth  to  the  plate  for  in- 
vestment; the  procedure  for  doing  this  is  the  same,  no  matter  by  what 
method  the  rim  has  been  constructed.  Naturally,  one  would  think 
that  this  could  be  accomplished  by  simply  heating  the  plate  so  that  it 
would  soften  the  adhesive  wax,  placing  it  upon  the  model,  and  then  press 
the  guides,  in  which  the  teeth  are  imbedded,  firmly  in  place.  If  the  rim 
has  been  swaged  and  riveted  to  the  plate  before  the  teeth  were  removed, 
this  will  often  give  accurate  results;  in  other  cases,  however,  it  is  very 
uncertain.  There  is  a  tendency  in  the  rim  to  creep  bodily  toward  the 
alveolar  ridge  during  soldering,  so  that  when  the  teeth  are  placed  in  it 
after  soldering  they  are  a  trifle  too  long,  not  enough  to  affect  seriously 
the  articulation,  but  enough  to  prevent  their  fitting  solidly  to  the  plate. 

Wax,  particles  of  plaster,  slight  changes  in  the  form  of  the  plate,  etc., 
may  prevent  the  guides  fitting  exactly  as  they  originally  did.  In  order 
to  ensure  accuracy  in  this  respect,  before  removing  the  guides  from  the 
model  make  a  slight  cone-shaped  depression  in  the  guide  and  another 
immediately  below  it  in  the  model  at  about  the  median  line;  into  these 
adjust  the  point  of  a  pair  of  dividers,  and  accurately  measure  and  note, 
or  mark  their  distance  apart  on  some  portion  of  the  model,  so  that  the 
dividers  can  be  again  set  in  the  same  position.  It  is  only  necessary  to 
apply  the  dividers  again  to  these  points  to  determine  when  the  guide  is  in 
its  original  position.  In  many  cases  it  is  necessary  to  remove  a  portion  of 
the  wax  and  to  cut  the  plaster  away  from  the  guide  so  as  to  free  the  plate 
entirely  before  it  will  fit  in  its  original  position,  not  disturbing,  however, 
that  portion  which  rests  upon  the  back  part  of  the  model.  Occasionally 
it  is  necessary  to  grind  the  ends  of  the  gums;  this  should  be  done  care- 
fully, and  not  until  it  is  found  absolutely  necessary;  usually  a  little  taken 
from  the  plate  side  of  their  extreme  ends  will  be  sufficient.  This  can  gen- 
erally be  done  without  removing  the  teeth  from  the  guide.  If  the  teeth 
are  kept  together  and  not  removed  from  the  guide,  one  may  depend 
upon  accurately  replacing  them;  if  they  are  removed,  it  is  very  difl&cult 
to  replace  them  without  some  slight  changes  in  their  position. 

After  the  teeth  are  accurately  fitted  to  the  rim,  so  that  the  guide  with 
the  teeth  imbedded  in  it  will  go  on  the  model  in  its  original  position. 


614  SWAGED  METALLIC  PLATES. 

secure  the  plate  to  the  teeth  "vvith  adhesive  wax  and  remove  the  plate 
and  teeth  thus  held  together  from  the  model,  and  add  a  coating  of  invest- 
ing material  to  cover  the  rim  and  exposed  ends  of  the  teeth,  letting  it 
extend  under  tlie  plate.  When  this  has  set,  remove  the  outer  portion 
of  the  guides,  that  portion  which  covers  the  face  of  the  teeth  and  which 
was  made  so  as  to  be  removable;  cut  from  the  remaining  portion  so  as  to 
expose  one-third  of  the  grinding  surfacesof  the  molars  and  bicuspids, 
and  add  a  fresh  portion  of  investment,  allowing  it  to  cover  all  exposed 
portions  of  the  teeth  and  to  overlap  the  portion  first  added,  wetting  this 
with  water  so  that  the  two  will  unite.  When  this  has  set,  carefully  remove 
the  remaining  portion  of  the  guide,  heating  the  plate  to  soften  the  wax 
and  permit  its  removal.  If  any  teeth  are  disturbed  during  this  operation, 
they  should  be  replaced  and  made  secure.  After  wrapping  this  pre- 
liminary investment  with  binding  wire  as  a  precaution  against  the  in- 
vestment cracking,  the  investment  of  the  denture  is  completed  in  the 

Fig.    o54 


Upper  denture  rimmed. 

usual  manner,  [f  this  procedure  has  been  carefully  carried  out,  there  will 
be  no  material  change  in  the  position  of  the  teeth,  and  much  less  time  will 
have  been  occupied  than  if  the  teeth  had  been  separately  adjusted  to 
position,  with  the  further  advantage  that  the  even  gum  line  made  as  the 
first  step  toward  the  construction  of  the  rim  will  have  been  preserved 
throughout.  The  changes  in  technique  for  rimming  a  full  upper  or 
lower  or  a  partial  upper  or  lower  denture  are  so  slight  that  further  de- 
scription is  unnecessary. 

After  the  teeth  are  soldered,  the  first  step  toward  finishing  the  rim  is  to 
make  its  free  edge  fit  closely  to  the  gums  of  the  teeth;  this  is  accomplished 
by  the  use  of  the  burnisher  and  the  file — the  burnisher  to  bend  the 
edge,  and  the  file  to  thin  the  edge  when  it  is  too  thick  for  the  burnisher 
to  bend  it.  This  accomplished,  by  the  use  of  suitable  tools  the  rim  is 
to  be  given  smooth  and  even  surface.  The  finished  riii\  is  shown  in 
Fig.  554. 

The  operation  of  burnishing,  when  the  object  is  to  change  the  shape  of 
a  piece  of  metal,  is  analogous  to  "metal-spinning,"  and  is  very  different 
from  burnishing  to  produce  a  hardened  pohshed  surface;  in  the  first  the 
burnisher  is  used  with  considerable  pres.sure,  its  motion  is  slow  and  de- 
liberate, so  as  to  effect  the  desired  change  before  the  metal  has  lost  the 
softening  effect  of  annealing  and  become  hard  and  elastic.   In  the  second 


WIRING  PLATES.  615 

the  pressure  is  light  and  the  motion  rapid,  an  effort  is  made  to  condense 
and  harden  the  surface  so  that  it  will  receive  and  retain  a  high  polish. 


WIRING  PLATES. 

^Mien  plain  teeth  have  been  adapted  to  a  plate,  and  it  is  designed  to 
place  over  them  an  artificial  gum  of  one  of  the  vegetable  bases,  it  is 
advisable  to  attach  to  the  labial  and  buccal  edge  of  the  plate  a  contin- 
uous wire,  to  round  the  edge,  increase  the  means  of  retention  of  the  arti- 
ficial gum,  and  to  lend  additional  beauty  of  finish  to  the  piece.  After  the 
teeth  have  been  fitted  and  tried  in  the  mouth,  the  palatal  line  of  the  base 
of  the  last  molar  of  each  side  is  marked  by  a  scratch  on  the  plate.  Be- 
ginning at  this  point  at  one  side,  a  wire  is  curved  over  the  ridge  and  to 
follow  the  edge  of  the  plate  until  it  terminates  at  the  base  of  the  opposite 
terminal  molar:  the  stays  of  these  teeth  are  to  abut  with  the  ends  of  the 
wire.  A  piece  of  triangular  wire  No.  18  gauge  of  the  proper  length  is  pro- 
cured. Tliis  is  annealed,  boiled  in  the  acid  solution,  and  one  face  of  it 
scraped  to  exhibit  a  fresh  surface.  The  middle  of  the  wire  is  usually 
attached  first.  A  clamp  holds  that  point  of  the  wire  against  the  plate  at  the 
depression  for  the  frsenum,  the  edge  of  the  wire  level  with  the  edge  of  the 
plate,  which  is  then  set  on  a  block  of  charcoal,  the  alveolar  ridge  portion 
resting  upon  the  surface  of  the  latter.  The  point  of  junction  of  the  wire 
and  plate  is  covered  with  borax  and  a  small  piece  of  solder  placed  over  it. 
A  fine  blowpipe-flame  is  directed  against  the  plate  beneath  the  wire 
carefully  avoiding  contact  of  the  flame  with  the  loose  ends  of  the  wire, 
as  these  latter  fuse  very  readily.  When  the  solder  flows,  attaching  the 
%vire  at  this  one  point,  the  clamp  is  removed  and  the  plate  plunged  in 
the  sulphuric  acid  solution.  The  plate  is  placed  upon  the  model  or  die 
and  the  wire  bent,  following  the  line  of  the  plate.  For  about  half  an 
inch  on  both  sides  of  the  soldered  point  the  wire  is  brought  into  close 
apposition  with  the  plate,  the  edges  of  wire  and  plate  in  a  fine;  the  junc- 
tion is  boraxed,  and  held  in  place  with  a  clamp  or  with  binding  wire,  and 
joined  to  the  plate  by  small  pieces  of  solder.  The  remainder  of  the  wire 
is,  little  by  little,  fitted  and  soldered  until  the  extremities  are  attached  and 
are  soldered  fast  to  the  point  at  which  the  disto-palatal  corner  of  the  sec- 
ond molar  touches  the  plate.  As  a  final  measure  the  entire  length  of 
the  joint  between  the  plate  and  wire  is  covered  by  borax,  one  or  two 
small  pieces  of  solder  placed  at  points  where  the  solder  may  be  deficient 
in  amount,  and  then  the  blowpipe  flame  is  passed  along  the  joint,  filling 
the  latter  completely  with  the  solder. 

Should  the  case  be  one  retained  by  clasps  the  wire  is  to  be  attached 
before  the  clasps  are  fastened  to  the  plate.  Before  rimming  or  wiring 
it  should  be  determined  whether  the  plate  edge  is  of  the  proper  height 
or  depth,  for,  should  subsequent  trimming  of  this  portion  of  the  plate 
be  required,  it  is  possible  that  a  portion  of  the  wire  might  have  to 
be  filed  away,  and  thus  mar  the  finish  of  the  denture. 

Cases  which  have  the  third  molars  remaining  should  have  the  wire 


616  SWAGED  METALLIC  PLATES. 

carried  around  the  plate  at  tlie  ])ase.s  of  tliese  teeth  (FiV.  555),     Tliis 
device  may  he  used  on  upper,  lower,  full  or  ])artial  dentures. 

If  the  teeth  have  been  fitted  to  the  j)late  before  the  \virin<>;  i.s  done 
they  may  be  held  together  by  plaster  guides,  and  invested,  nuieh  in  the 
same  way  that  gum  teeth  are  in  rimming.  It  is  usualh ,  however, 
better  to  wire  the  plate  first,  l(>aving  the  ends  extending  around  the 
molars  to  be  soldered  when  the  backings  are  soldered. 

Fig.  •■)-')5 


A  metallic  upper  plate  intended  for  a,  plain  tooth  denture,  wired  along  its  upper  edge. 

If  the  teeth  are  to  be  attached  to  the  plate  l)y  means  of  vulcanite  the 
wire  is  continued  across  the  palatal  aspect  of  the  palate,  following  a  line 
which  marks  the  base  of  the  wax.  A  pair  of  special,  long  clamps  will 
be  required  to  hold  the  wire  in  contact  with  the  plate  during  the  solder- 
ing operation. 

PREPARING  THE  CASE  FOR  INVESTING. 

All  dentures  of  plain  teeth,  and  partial  dentures  of  gum  teeth  where 
they  stand  alone,  or  where  not  more  than  two  or  three  are  together, 
usually  need  no  preparation  for  investing  beyond  seeing  that  the  teeth 
are  held  so  securely  by  the  adhesive  w^ax  that  there  is  no  danger  of  their 
displacement  when  the  denture  is  imbedded  in  the  investment;  but  in 
cases  where  the  gums  are  very  long  and  are  not  supported  by  the  plate, 
or  have  been  ground  very  thin,  it  is  a  wise  precaution  to  place  a  drop 
of  yellow  wax  inside  the  weak  gums,  so  as  to  prevent  the  plaster  from 
coming  into  actual  contact  with  them,  and  thus  lessen  the  risk  of  their 
being  broken  when  the  case  is  removed  from  the  investment  after  solder- 
ing. 

In  cases  where  there  are  a  number  of  gum  teeth  together  with  the 
gums  closely  jointed,  some  provision  must  be  made  to  prevent  accident 
from  their  expansion  when  heated  for  soldering.  If  this  is  not  done, 
there  is  serious  risk  of  chipy)ing  at  the  edges  where  they  are  jointed  to- 
gether, or  the  teeth  may  be  so  broken  as  to  require  replacement.     In 


INVESTING.  617 

addition  to  this  tlienMS  also  a  risk  of  the  plate  warping  tlnring  soldering: 
where  in  lower  dentures  this  oeeurs  the  plate  usually  eui'ves  inward,  the 
distal  ends  being  brouglit  nearer  together;  in  ujjper  dentui'es  the  ehange 
in  shape  makes  the  plate  press  upon  the  hard  palate,  producing  what 
is  known  as' a  "side  rock." 

To  prevent  these  aceitlents  take  a  strip  of  thin  soft  paper,  such  for 
instance,  as  the  margin  of  a  newspaper,  and,  beginning  at  the  centrals, 
remove,  one  at  a  time,  each  alternate  tooth,  and  place  in  the  joint  be- 
tween the  gums  a  thickness  of  paper,  slightly  wetting  it  so  that  it  will  lay 
flat,  removing  from  the  tooth  with  a  grindstone  a  sufficient  amount  to 
allow  for  it.  During  soldering  this  paper  is  burned  out  before  the  heat 
has  expanded  the  porcelain  to  any  great  degree,  leaving  between  the 
teeth  a  slight  space;  if  carefully  done,  however,  the  space  made  is  so 
slight  as  to  be  unnoticed  in  the  finished  denture,  while  it  effectually 
prevents  the  accidents  referred  to.  To  remove  a  tooth  without  dis- 
placing the  adjoining  teeth,  pass  a  hot  wax  spatula  by  the  side  of  the  pins 
to  soften  the  wax  around  them,  and  then  push  it  off.  If  this  is  done 
carefully  the  wax  is  left  so  that  the  tooth  can  be  accurately  replaced,  an 
application  of  the  wax  spatula  securing  it  in  place  again. 


INVESTING. 

An  investment  is  a  device  designed  to  hold  the  teeth  and  plate  in 
their  relative  positions  during  the  soldering  operation.  It  is  made  of  a 
material  having  a  low  degree  of  heat  conductivity  and  sufficient  coher- 
ence to  ensure  that  it  shall  maintain  its  form  when  raised  to  a  very  high 
heat.  By  its  relatively  low  conductivity  it  prevents  too  rapid  heating  of 
the  porcelain  teeth  it  encloses,  and  also  the  too  rapid  cooling  when  the 
source  of  heat  is  removed;  either  of  which  is  a  prominent  factor  in. 
casing  fractures  of  porcelain.  The  same  physical  property  lends  to 
the  investing  material  the  feature  of  maintaining  the  teeth  at  a  constant 
temperature  during  the  soldering  operation.  Plaster  of  Paris  is  the 
basis  of  the  investment;  to  it  are  added  beach  sand  or  asbestos,  so  as  to 
overcome  its  tendency  to  contract  and  to  fracture  when  heated  to  a  sol- 
dering temperature.  About  five  parts  of  sand,  or  of  a  mixture  of  sand 
and  asbestos,  to  four  of  plaster,  makes  a  satisfactory  investment. 

Water  is  first  placed  in  a  plaster  bowl,  and  to  it  is  added  a  sufficient 
quantity  of  short-fibre  asbestos,  or  woolly  asbestos,  or  beach  sand  and 
asbestos,  until  the  materials  are  just  covered  by  a  film  of  water,  and  the 
mixture  is  well  stirred  to  distribute  the  asbestos  or  sand  evenly.  Plaster 
of  Paris  is  next  sifted  in  and  stirred  until  a  soft,  plastic  mass  is  made. 
About  a  spoonful  of  this  is  placed  upon  a  glass  slab,  making  a  layer 
about  half  an  inch  thick.  The  denture  is  wet  so  that  the  investing 
material  will  flow  freely  into  the  spaces  between  the  teeth.  A  portion 
of  the  material  is  taken  upon  the  point  of  a  spatula  and  worked  into  the 
deepest  portions  of  the  palatal  surface  of  the  plate :  little  by  little  more 
investment  is  quickly  added  until  the  plate  is  full,  when  the  material  is 


618  SWAGED  METALLIC  PLATES. 

tlien  packed  between  the  teeth,  filling  the  spaces  perfectly.  It  is  then 
inverted  upon  the  bed  of  the  material  upon  the  slal),  and  the  investment 
built  up  about  the  teeth  until  they  are  covered  by  a  layer  half  an  inch 
thick.  The  lingual  surface  of  the  plate  is  covered  to  within  about  half 
an  inch  of  the  bases  of  the  teeth.  To  ensure  against  fracture  of  the  in- 
vestment, a  piece  of  round-wire,  or  several  strands  of  binding-wire  formed 
into  a  ring  is  imbeded  in  the  investment.  This  is  so  bent  that  its  arch 
shall  be  about  a  quarter  of  an  inch  larger  than  that  of  the  teeth.  When 
binding  wire  is  used  (Fig.  556),  several  strands  formed  into  a  circle 
are  placed  over  the  teeth,  the  front  portion  a  little  below  the  cutting 
edges  of  the  teeth,  and  the  back  portion  is  bent  downward  to  about  the 
level  of  the  plate.  In  either  case  this  reinforcement  is  set  in  position 
when  the  investment  is  half  complete  and  thoroughly  imbedded  in  it. 

Fic.   556 


Several  strands  of  iron  binding-wire  formed  into  a  ring  to  reinforce  the  in^■estment  of  an  upper 
denture,  showing  the  relative  position  of  the  wire  and  the  plate. 

The  investing  material  is  harder,  but  more  friable  and  quicker  setting 
than  plaster  alone;    these  manipulations  must  be  quickly  done.      (Fig. 

557.) 

When  investing  delicate  partial  cases  it  is  better  to  have  the  material 
rather  thin,  placing  a  mass  of  it  upon  the  slab  and  then  carefully  laying 
the  case  upon  it,  work  it  down  with  a  gentle  rocking  motion  until 
there  is  rather  less  than  half  an  inch  under  the  deepest  part  of  the 
plate:  after  this  has  become  somewhat  set,  add  more  of  the  investment, 
building  it  up  to  and  around  the  teeth. 

The  investment  of  lower  dentures  differs  so  little  from  that  of  upper 
dentures  as  not  to  re(iuire  a  separate  description.      (Fig.  558.)  ^ 

When  investing  a  denture,  three  points  are  to  be  borne  in  mind: 
First,  be  sure  that  the  material  is  in  contact  with  the  under  surface  of 
the  plate  at  all  points,  especially  that  it  fills  the  bands  or  clasps  of 
partial  cases.  If  any  vacancies  exist  there  is  danger  of  the  plate  being 
overheated  and  burned  at  that  point,  or  of  sinking  in  and  thus  im- 


INVESTING.  619 

pairing-  tlie  fit  Second  see  that  the  teeth  arc  well  covered,  not  only  to 
hold  them  in  place  secnrelj,  bnt  also  to  protect  them  from  direct  contact 
witii  the  blowpipe-flame.      Third,  see  that  the  edges  of  the  plate  are 

Fig.    r,57 


An  upper  denture  invested,  and    prepared  for  making  the  backings  and  for  soldering.    A  por- 
tion fs  broken  away  to  show  the  terminal  of  the  reinforcing  wire  imbedded  in  the  investment. 

well  covered:  if  this  is  neglected  they  are  apt  to  curve  up.  It  is  de- 
sirable, however,  that  the  surface  of  the  plate  be  well  exposed;  for 
soldering,  otherwise  there  may  be  difficulty  in  getting  it  hot  enough 
(Figs.  557  and  558.) 

Fig.    558 


A  lower  denture  invested,  and  prepared  for  soldering.      A  portion  is  broken  away  to 
show    the  terminal  of  the  reinforcing  wire  imbedded  in  the  investment. 

Preparing  the  Invested  Denture  for  Making  the  Backings,  and  for  Solder- 
ing.— First,  trim  off  such  portions  of  the  investment  as  encroach  too  far 
over  the  plate  and  the  edges  of  the  teeth ;  being  careful,  however,  that 
while  removing  enough  to  give  free  access  to  the  teeth  for  making  the 


620  SWAGED  METALLIC  PLATES. 

li.-ickiiigs,  aiul  ('X])().siiio;  all  portions  over  wliicli  solder  is  to  be  flowed  so 
that  they  can  he  readily  reached  hy  the  hlowpipe-llanie,  that  enoutrh  is 
left  to  hold  the  teeth  securely  and  to  protect  all  parts  liable  to  be  injured 
by  unnecessary  contact  with  it.  Then,  remove  all  i-edundant  portions 
and  trim  to  a  neat  easily  handled  shape. 

Next,  remove  the  adhesive  wax,  which  to  this  point  has  held  the  teeth 
in  place.  This  should  be  done  mechanically;  the  use  of  heat,  wet  or  dry, 
is  inadmissible.  A  fine  pointed  instrument,  or  the  narrow  blade  of  a 
pen-knife,  is  an  effective  tool  for  this  purpose.  Care  is  needed  in  this 
operation  to  avoid  fracturing  the  teeth  by  getting  the  instrument  between 
their  pins,  or  displacing  the  teeth.  By  picking  and  scraping  every 
particle  of  wax  under,  between,  and  around  the  teeth  must  be  re- 
moved, and  the  plate  surface  over  which  solder  is  to  flow  made  clean  and 
bright,  especially  if  the  plate  is  of  silver.  The  pins  should  next  re- 
ceive attention,  and  be  made  clean  and  free  from  porcelain  or  other 
foreign  matter  adhering  to  them.  Partial  dentures  require  during  this 
operation  very  gentle  handling.  Teeth  standing  alone  are  easily  dis- 
placed, and  the  gums  of  gum  teeth  are  readily  broken. 

If  the  backings  have  been  previously  made,  the  denture  is  now  ready 
for  soldering;  if  this  has  not  been  done,  it  may  now-  be  proceeded  with. 

MAKING  THE  BACKINGS. 

As  a  general  rule  for  all  full  dentures,  and  for  all  but  the  smaller 
partial  dentures,  it  is  more  satisfactory  to  fit  the  backings  after  the  teeth 
are  invested.  When  the  denture  has  been  finally  tried  in  the  mouth 
with  the  teeth  cemented  in  place,  it  is  a  serious  risk  to  remove  them 
again  from  the  plate;  notwithstanding  the  careful  use  of  guides,  slight 
changes  of  position  are  inevitable,  and  the  artistic  and  mechanical 
adjustment  thereby  endangered. 

Before  beginning  to  make  the  backings  for  a  full  denture,  have  the  fol- 
lowing tools  close  at  hand  upon  the  workbench:  the  plate  shears; 
punch  for  rivet  holes  (select  for  this  purpose  a  punch  with  short  jaws; 
many  are  made  with  the  jaws  so  long  as  to  require  a  strong  force  to  per- 
forate the  thick  metal  used  in  making  backings);  a  strong  pair  of  flat 
pliers  (not  too  large),  with  beaks  that  will  hold  firmly;  a  five  inch  half- 
round  file;  a  point  that  can  be  used  as  a  reamer;  a  tool  for  countersink- 
ing the  rivet  holes — a  large,  obtuse-pointed  spear  drill,  or  a  triangular 
scraper  answers  for  this  purpose;  a  small  hammer;  the  bench  anvil;  a 
pair  of  broad  tweezers  or  solder  tongs;  and  a  chisel  for  splitting  the  pins. 

The  thickness  of  metal  to  be  used  for  backings  will  depend  upon  the 
length,  position,  and  character  of  the  teeth.  Plain  teeth,  and  all  teeth 
that  stand  alone  require  stronger  backings  than  do  gum  teeth,  where 
the  backings  may  be  united  a  portion  of  their  length.  Long  teeth  and 
very  narrow  teeth  refpiire  stronger  backings  than  do  short  or  wide 
teeth.  Gold  backings  should  be  about  No.  22  gauge,  silver  about  two 
numbers  heavier.  The  addition  of  a  little  platinum  to  the  gold  used 
for  backings  gives  them  greater  strength  and  stiffness. 


MAKIXG  THE  BACKIXGS  621 

The  hackings  should  be  made  nearly  as  wide  as  the  teetli.  The 
length  is  sometimes  a  matter  of  taste;  at  other  times  it  will  depend  upon 
the  requirements  of  the  case.  If  the  anterior  teeth  are  likely  to  be  sub- 
jected to  much  strain  in  mastication,  their  backings  should  extend 
quite  to  the  cutting  edges,  so  that  the  opposing  teeth  will  strike  against 
them  rather  than  against  the  teeth.  In  other  cases  they  should  terminate 
about  half  way  between  the  upper  pin  and  the  cutting  edge;  this  leaves 
the  cutting  edge  more  translucent.  The  backings  should  be  uniform  in 
height  and  shape,  have  the  corners  rounded  and  their  surfaces  neatly 
curved  to  a  convex  form.     (Fig.  559.) 

^Yhen  backings  are  to  be  made  for  a  full  denture,  it  is  time-saving  to 
cut  several  strips  of  metal,  about  two  or  three  inches  long,  and  of  suit- 
able width,  bevelling  for  their  entire  length  both  edges  upon  that  side 

Fig    559 


Upper  denture  ready  for  tho  mouth. 


vrhich  is  to  be  the  face  of  the  backing:  the  strip  is  more  quickly  bev- 
eled than  would  be  the  separate  backings.  An  upper  denture  requires 
the  same  width  for  the  centrals  and  molars,  another  width  for  the  later- 
als and  bicuspids  and  canines,  so  that  if  each  strip  is  cut  slightly  wider 
at  one  end  than  at  the  other,  two  strips  will  make  all  the  backings.  A 
lower  denture  usually  requires  three  strips  differing  in  width;  one  for 
the  six  anterior  teeth,  one  for  the  bicuspids  and  one  for  the  molars. 

The  author  prefers  to  begin  ^-ith  the  centrals  in  making  and  finishing 
the  backings,  making  them  in  pairs,  as  by  so  doing  they  can  be  made 
more  uniform.  Ha^'ing  prepared  the  strips,  place  one  before  the  tooth 
to  be  fitted,  and,  holding  it  in  the  position  the  backing  will  occupy,  pro- 
ceed to  make  the  end  resting  on  the  plate  fit  the  plate  accurately  by  cut- 
ting with  the  shears  or  by  filing.  "Wlien  this  is  done,  mark  the  position 
of  the  pin-holes  by  placing  it  in  position  and  while  pressing  it  firmly 
against  the  pins  impart  to  it  a  slight  movement  so  that  it  will  rub  against 
at  least  one  pin.  This  will  accurately  mark  where  the  pinhole  is  to  be 
punched.  Punch  a  hole  at  the  pin-mark  most  plainly  to  be  seen,  and 
after  countersinking  this  hole  proceed  in  like  manner  to  mark  the  posi- 


622  SWAGED  METALLIC  PLATES. 

tion  of  tlie  remaining  pin.  This  method  of  determinig  the  position  of 
the  pin-holes  has  been  satisfactory  to  the  author  for  more  than  two  score 
of  years;  it  is  cleanly,  requires  no  additional  tools  or  appliances,  is  quick- 
ly done  and  is  accurate.  If  the  holes  when  punched  are  too  far  apart, 
or  to  close,  so  that  force  is  required  to  press  the  backing  in  place,  there  is 
dan<rer  of  the  tooth  being  broken  in  soldering.  To  remedy  the  first 
defect  slightly  enlarge  one  or  both  iioles  by  punching  a  little  from  the 
inner  side:  the  second  defect  is  corrected  by  laying  the  strip  upon  the 
anyil  and  striking  a  few  light  blows  with  the  blade  of  the  hammer  be- 
tween the  holes;  this  will  spread  then  farther  apart.  Countersink  the 
holes  slightly  on  the  side  next  the  tooth,  but  quite  freely  on  the  other 
side,  and  remove  the  burr  raised  by  the  countersink.  Then  lay  the  strip 
flat  on  the  bench,  with  the  side  that  goes  next  the  tooth  uppermost,  and 
strike  a  sharp  V^low"  with  the  blade  of  the  hammer  about  the  centre  of  its 
width,  and  near  that  end  of  the  strip  which  has  been  fitted  to  the  plate. 
The  object  of  this  is  to  curve  it  slightly  so  that  its  edges  will  fit  more 
closely  to  the  back  of  the  tooth.  Then  place  it  upon  the  tooth  and  see 
that  it  fits  soHdly ,  and  closely  at  the  edges,  and  mark  where  it  is  to  be  cut 
off,  making  the  front  side  a  little  higher  so  that  it  will  be  parallel  with 
the  cutting  edge  of  the  tooth.  Cut  it  off  and  lay  it  aside,  and  proceed  in 
like  manner  until  all  the  backings  for  the  denture  in  hand  have  been 
fitted,  cut  off,  and  arranged  in  order.  The  backings  for  the  centrals  are 
now  filed  into  proper  shape,  and  made  as  nearly  alike  as  possible,  then 
the  laterals,  and  so  on  until  all  are  completed.  If  the  denture  is  of  plain 
teeth,  the  backings  may  now  be  fixed  in  position  by  splitting  the  pins 
crosswise,  and  the  preparation  for  soldering  proceeded  with.  If  of  gum 
teeth,  connecting  pieces  betw^een  the  backings  must  first  be  fitted,  un- 
less this  has  been  provided  for  when  finishing  the  backings. 

In  all  cases  of  plain  teeth  the  backings  must  follow  the  outline  of  the 
tooth,  being  made  quite  as  wide  but  no  wider,  otherwise  they  will  be 
seen  through  the  interspaces.  In  cases  of  gum  teeth,  if  the  strips  from 
which  the  backings  are  made  have  been  first  beveled,  as  suggested,  the 
backings  are  filed  into  shape  precisely  as  though  they  Avere  for  plain 
teeth,  no  attention  being  paid  to  the  offset  marking  the  gum  portion  of 
the  teeth  until  after  the  backings  have  been  finished;  then,  preparatory 
to  soldering  them  to  the  plate,  in-between-pieces  are  fitted  to  make  the 
backings  continuous  as  high  as  these  offsets  extend  in  the  following 
manner:  narrow  pieces  of  thin  platinum  plate  (the  thicker  platinum 
foil  prepared  for  inlay  work  is  satisfactory),  are  cut  extending  from  the 
top  of  the  gum-joint  between  the  teeth  to  the  plate,  and  wide  enough  to 
be  firmly  held  by  the  sides  of  the  backings.  Before  the  backings  are 
fastened  to  the  teeth  these  pieces  are  pressed  across  the  joints,  fitting  any 
irregularities  of  form  which  may  be  present,  the  backings  are  placed  in 
position  in  pairs,  so  that  by  splitting  and  bending  down  the  pins  the  sides 
of  the  backings  hold  the  platinum  pieces  firmly  in  position.  When  all 
the  backings  have  been  adjusted  and  fastened,  small  pieces  of  metal 
the  same  as  that  of  which  the  backings  are  made,  are  beveled  to  fit  the 
sides  of  adjoining  backings,  and  long  enough  to  hide  the  platinum :  l)e- 


MAKING    THE  BACKINGS. 


623 


fore  placing  them  for  soldering  the  surface  of  platinum  is  covered  by 
borax,  the  small  sections  covered  also  with  borax,  and  placed  in  position. 

An  alternative  method  is  to  make  the  backings  wide  enough  to  overlap 
slightly,  and  when  filing  them  into  shape  to  form  a  shoulder  on  each  side 
slightly  lower  than  the  top  of  the  gum-joint ;  one  side  of  this  portion  is 
beveled  outward  and  the  other  inward,  and  the  backings  neatly  fitted, 
the  one  to  the  other,  so  that  this  portion  of  the  backings  forms  a  con- 
tinuous level  surface  (Fig,  560.)  That  for  the  last  molar  is  bent  to  meet 
the  rim.  If  this  is  well  done,  it  facilitates  the  soldering  very  much ;  there 
is  nothing  to  be  displaced,  less  solder  is  needed,  and  this  smooth  even 
surface  is  far  mort  (juickly  finished. 

In  most  partial  dentures  it  is  time  saving,  and  more  satisfactory  to 
make  the  backings  and  solder  and  finish  them  before  investing,  especially 
in  cases  where  teeth  stand  alone.  The  extra  time  lost  by  the  two  solder- 
ings  is  recovered  by  the  time  saved  in  finishing,  and  the  work  is  usually 
done  more  neatly.  If  the  case  calls  for  exactness  in  the  position  of  the 
teeth,  the  denture,  after  having  been  tried  in  the  mouth  is  placed  on  the 


Fig    560 


Backings  shaped  to  cover  the  gum-joint  and  forming  from  the  top  of  the  gum-joint  to 
the  plate  a  continuous  level  surface.  The  backing  of  the  last  molar  extends  around  that 
tooth  to  meet  the  rim. 

model,  and  plaster  guides  made  to  facilitate  their  replacement,  when 
these  are  hard,  remove  the  wax,  and  proceed  to  make  the  backing  pre- 
cisely as  though  the  denture  was  invested.  The  tooth  may  now  be  re- 
moved from  the  model  and  the  backing  fitted  to  the  tooth,  filed  into 
shape,  and  secured  to  the  tooth  by  splitting  the  pins  with  a  sharp  chisel 
or  graver  first  crosswise  and  then  lengthwise  of  the  tooth,  pressing  the 
split  portions  apart  so  as  to  form  a  head  to  the  pin  filling  the  counter- 
sink. The  tooth  is  now  invested  in  a  small  mass  of  investing  material 
(Fig.  561),  care  being  taken  that  no  portion  is  exposed  other  than  that 
over  which  the  solder  is  to  flow,  and  equal  care  that  no  investing  material 
is  allowed  to  reach  the  pins;  if  it  once  gets  there  it  is  exceedingly  difficult 
to  remove.  If  the  tooth  is  very  small,  and  this  is  liable  to  happen,  the 
pins  had  better  be  covered  by  a  little  mass  of  beeswax  softened  and 
pressed  into  position;  so  placed  it  will  thoroughly  protect  the  pins  and  is 
readily  removed.  It  is  advisable  when  soldering  the  backings  to  the 
teeth  before  they  are  invested  to  use  a  less  fusible  solder,  one  that  will  not 
be  reflowed  when  the  teeth  are  soldered  to  the  plate.  This  can  be  quickly 
made  by  adding  about  one-fourth  its  weight  of  plate  to  the  solder,  thor- 
oughly fusing  the  two  under  the  blowpipe  into  a  globule  and  forging  it  to 


624  SWAGED  METALLIC  PLATES. 

the  right  thickness.  This  holds  good  with  silver  solder,  and  with  gold 
solder  of  any  earat.  Where  a  number  of  teeth  are  to  be  thus  backed  and 
soldered,  the  author  has  not  found  it  advisable  to  place  more  than  two  in 
the  same  mass  of  investment;  if  a  number  are  invested  together  they  all 
must  remain  under  heat  until  the  last  is  soldered,  and  not  unfrequently 
those  first  soldered  are  put  to  more  risk  after  they  are  soldered  than 
during  the  operation,  because  attention  is  especially  directed  to  the  one 
under  the  blowpipe  and  an  accidental  deflection  of  the  flame  impinging  on 
the  others  may  escape  notice.  After  the  backings  have  been  soldered  and 
cleansed  in  acid  they  should  be  filed  to  shape  and  polished  with  a  felt 
wheel  before  being  invested,  as  this  can  be  more  readily  done  now  than 
after  they  are  soldered  to  the  plate. 

If  the  surface  of  the  tooth  to  be  fitted  with  a  backing  is  especially 
irregular,  or  a  very  close  fitting  backing  is  required,  the  above  method 
may  be  modified  by  making  a  backing  of  thin  and  soft  plate,  securing 
it  to  the  tooth  by  splitting  the  pins,  and  then  wrapping  it  in  soft  paper, 
place  it  in  a  small  "shot-swage"  upon  a  bed  of  corn  meal,  fill  the  swage 
with  corn  meal  and  press  it  firmly  between  the  jaws  of  a  bench  vise. 

Fig.  561 


Teeth  iinestcil  to  scililei-  the  liackings. 


This  thin  backing  is  thus  brought  into  absolute  contact  with  the  porce- 
lain of  the  tooth.  The  pins  will  usually  be  found  projecting;  they  are 
again  pressed  apart  and  in  contact  with  the  backing,  and  a  second 
backing  of  thicker  metal,  slightly  smaller,  and  without  pin-holes,  is  pre- 
pared to  fit  over  the  first  and  laid  aside  after  being  coated  on  the  inner 
side  with  borax.  The  tooth  with  the  first  backing  in  place  is  now  in- 
vested, provision  being  made  for  placing  the  second  backing  in  position. 
The  backing  is  now  soldered,  the  solder  being  allowed  to  flow  over  it, 
the  second  backing  placed  in  position  and  heat  again  applied  to  re-fuse 
the  solder  so  as  to  unite  the  two  thoroughly. 

In  many  partial  cases  the  backings  may  be  fitted,  soldered,  and  fin- 
ished, before  the  teeth  are  fully  fitted  into  position.  In  these  cases  the 
backings  are  made  to  extend  to  the  base  of  the  tooth,  and  are  fitted  to 
the  plate  by  the  grindstone  at  the  same  time  as  the  teeth  are  fitted. 
Now  and  again  it  is  desirable  to  do  this,  especially  when  the  bite  is 
very  close;  the  tooth  being  tried  in  the  mouth  with  the  backings  in 
place,  ensures  that  it  will  not  be  in  the  way  after  the  denture  is  com- 


PREPARING  FOR  SOLDERING.  62-') 

pleted.     This,  however,  makes  the  trying  in  more  diflBcuIt,  as  the  teeth 
are  held  less  securely  to  the  plate. 


PREPARING  FOR  SOLDERING. 

When  preparing  a  plain  tooth  denture  for  soldering,  first  fit  between 
the  backings  little  triangles  of  metal  so  as  to  connect  them  together  at 
the  plate  line.  These  may  be  clipped  from  a  piece  of  plate  with  the  shears ; 
the  point  which  passes  between  the  teeth  should  entirely  fill  the  space, 
and  may  require  bevelling  on  its  under  side  so  as  to  fit  close  to  the 
plate,  and  not  show  through  the  interspace;  the  base  of  the  triangle 
should  be  even  with  the  backings.  These  pieces  add  very  much  to  the 
strength  of  the  denture,  facilitate  soldering,  and  permit  a  neater  finish. 
A  similar  piece  should  be  fitted  to  the  back  part  of  the  last  molar  of 
each  side.  Plaster  or  whiting,  mixed  with  water,  is  now  packed  be- 
tween the  teeth,  over  the  tops  of  the  backings,  and  in  every  space  where 
there  is  danger  of  borax  reaching  the  porcelain,  or  where  the  invest- 
ment does  not  thoroughly  protect  the  teeth.  All  parts  over  which  the 
solder  is  to  flow  require  to  be  coated  vdth  borax,  ground  with  water  to  a 
creamy  consistency;  solder  is  now  added,  very  small  pieces  over  each 
pin,  and  a  line  of  pieces  about  three-sixteenths  of  an  inch  long  and  one- 
sixteenth  wide,  are  laid  at  the  junction  of  the  backings  with  the  plate. 
This  done,  the  denture  is  ready  for  heating  preparatory  to  soldering. 

Much  the  same  procedure  is  required  in  the  case  of  gum  teeth,  a 
little  more  care  is  needed  in  placing  the  protective  investment  between 
the  teeth  if  the  connecting  pieces  are  separate  from  the  backings,  as  it 
is  depended  upon  to  hold  them  in  place.  The  arrangement  of  solder 
must  also  provide  for  uniting  the  backings.  The  last  molar  of  each 
side  must  be  connected  with  the  rim,  either  by  bending  the  free  portion 
of  the  rim,  left  unsoldered  for  that  purpose,  close  to  the  gum  portion 
of  the  tooth,  or  by  an  additional  piece  if  this  proves  too  short.  If  there 
is  no  rim,  a  triangular  piece  of  plate  should  be  fitted  to  this  part  for  the 
sake  of  a  neater  finish. 

Partial  dentures  require  in  addition  to  this,  reinforcing  pieces  over 
narrow  portions  of  the  plate  supporting  scattered  teeth.  These  should 
connect  with  the  backings  and  extend  sufficiently  far  over  the  plate 
to  impart  the  required  strength  and  rigidit}' .  The  general  reinforcing 
of  the  plate  is  best  done  when  the  plate  is  made;  those  points  especially 
liable  to  change  of  form  or  fracture,  are  reinforced  when  the  teeth  are 
soldered.  At  this  time  the  union  of  the  clasps  and  plate  is  made  more 
secure  either  by  additional  solder  or  adding  pieces  of  plate;  care  being 
taken,  however,  to  protect  that  portion  of  the  joint  which  it  is  desired 
to  remain  unsoldered  by  filling  it  with  plaster  or  whiting.  Wherever 
around  the  necks  of  the  natural  teeth  the  plate  is  subject  to  strain  it 
should  be  reinforced.  In  reinforcing,  dependence  should  be  placed 
upon  plate,  rather  than  upon  solder;  the  pieces  of  plate  used  should  be 
neatly  fitted,  the  edges  having  first  been  bevelled.     The  borax,  with 

40 


G26  SWAGED  METALLIC  PLATES. 

which  the  under  surface   should  be  coated   can  usually  be  depended 
upon  to  hold  them  in  place  during  soldering. 

SOLDERING. 

General  Considerations. — The  follow  ing  rules  are  to  be  observed  in  sol- 
dering: 

When  two  pieces  of  metal  are  to  })e  united  by  solder  their  surface 
should  be  as  nearly  as  possible  in  perfect  contact. 

The  solder  used  for  dental  appliances  should  be  employed  merely 
as  a  uniting  agent,  and  beyond  the  amount  necessary  to  perform  this 
office  it  should  form  no  part  of  a  fixture.  Any  additional  strength  of 
the  piece  should  be  derived  from  additions  of  plate,  not  of  solder. 

Absolute  chemical  cleanliness  of  the  surfaces  to  be  united  is  necessary. 

The  thickest  part  of  an  investment  is  to  receive  the  greatest  volume 
of  heat. 

Solder  flows  toward  the  parts  of  highest  temperature,  so  that  in  sol- 
dering, the  part  into  or  over  which  solder  is  to  be  flowed  is  made  hotter 
than  its  surroundings. 

With  decrease  in  the  thickness  of  the  solder  pieces,  there  is  an  in- 
creased surface  of  oxidation. 

Solder  should  be  placed  at  short  intervals  on  the  part  of  the  fixture 
most  difficult  to  heat. 

Drying  of  the  investment  should  precede  the  heating  of  it. 

No  tooth  should  receive  the  direct  flame  of  the  blowpipe  until  it  is 
heated  to  redness  by  heat  transmitted  through  the  investment  from  the 
exterior. 

Borax  must  not  be  placed  on  porcelain:  it  forms  a  contractible  glass 
surface  which  in  contracting  produces  enamel  fracture. 

In  any  piece  where  there  may  be  several  soldering  operations,  begin 
with  a  higher  carat,  or  a  less  fusible  solder,  but  in  no  case,  and  under  no 
circumstances,  use  on  new  work  a  solder  of  a  lower  carat  than  the  plate. 
The  fusing  point  of  any  grade  of  solder  may  be  raised  by  adding  to  it 
a  portion  of  the  same  metal.  Eighteen  carat  gold  plate  can  usually  be 
soldered  with  twenty-two  or  twenty  carat  solder,  under  favorable  cir- 
cumstances, if  care  is  used.  A  workman,  to  whom  a  case  is  given  for 
repairs,  has  a  right  to  assume  that  it  is  of  the  same  carat  throughout,  the 
attempt  to  use  an  appropriate  solder  would  prove  disasterous  if  in  its 
original  construction  a  low  carat  solder  had  been  used. 

SOLDERING  AND  FINISHING. 

The  denture,  with  the  solder  in  place,  is  slowly  heated  over  a  gas 
flame,  or  in  a  charcoal  furnace  until  the  whole  mass  of  the  investment  is 
at  a  red  heat.  There  are  two  forms  of  blowpipe  in  use.  In  the  older 
form  the  lilowpipe  is  practically  stationary,  and  the  work  is  brought  to, 
and  manipulated  under  it.      The  newer  form  can  readily  be  directed  in 


SOLDERING  AND  FINISHING.  627 

any  direction.  When  this  latter  form  is  used  the  denture  may  remain 
upon  the  heating  arrangement  during  the  soldering  operation.  The 
details  of  soldering  a  denture  can  be  learned  only  by  observation  and 
practice.  Whether  the  denture  remains  fixed,  or  is  transferred  to 
some  form  of  movable  support,  while  the  blowpipe  is  manipulated,  the 
proceedure  is  much  the  same. 

The  broad  blowpipe  flame  is  thrown  beneath  the  investment  and 
passed  rapidly  over  its  outer  wall,  until  the  teeth  and  backings  are 
made  red  by  the  transmitted  heat  and  the  solder  begins  to  settle.  The 
fine  flame  is  now  thrown  upon  the  line  of  junction  between  the  back- 
ings and  plate,  and  carried  from  the  terminal  molar  of  one  side  to  that 
of  the  other,  the  solder  melting  and  flowing  freely.  Usually  the  solder 
above  the  pins  and  lateral  joints  is  fused  by  the  same  flame;  if  not,  if 
it  does  not  flow  freely  about  the  pins  and  between  the  joints,  a  very 
pointed  flame  is  directed  at  each  pin  and  joint.  More  solder  is  added 
as  it  is  needed;  when  it  is  obstinate  it  may  be  "coaxed"  to  the  desired 
point  by  a  pointed  wooden-handled  steel  rod,  long  enough  for  com- 
fortable use.  This  rod  should  be  kept  sharply  pointed  and  clean.  To 
flow  as  it  should  the  solder  exhibits  a  quick  fluidity  and  has  a  smooth, 
even  surface  at  the  completion  of  the  operation.  The  case  is  now  per- 
mitted to  cool  slowly.  When  the  backings  are  cooled,  this  is  the 
test  for  the  proper  time  of  removing  the  investment;  the  latter  is  care- 
full}'  broken  away  piecemeal.  To  avoid  breaking  long  or  thin  gums 
the  investment  should  be  softened  by  being  placed  in  warm  water. 
The  leeth  and  gums  are  now  examined  for  any  possible  cracks  or 
checks,  as  they  are  more  readily  seen  while  the  case  is  dry.  The  piece 
is  boiled  in  the  acid  solution,  washed,  scrubbed  with  soap  powder,  and 
dried,  and  then  placed  on  the  model. 

If  the  preceding  operations  have  all  been  done  correctly,  the  plate 
will  have  suffered  no  change  of  form  and  the  porcelain  will  be  intact. 
If,  however,  there  has  been  any  neglect  of  the  minutia^,  all  of  vital  im- 
portance, the  plate  may  be  warped,  the  porcelain  gums  checked,  or  one 
or  more  teeth  cracked  or  in  malposition.  If  the  pieces  have  been  accu- 
rately fitted  and  no  excess  of  solder  used,  the  succeeding  operations  are 
a  comparatively  light  task,  but  none  the  less  important.  A  small  fine 
corundum  wheel  on  the  lathe  is  used  to  grind  down  the  heads  of  the  pins 
and  to  make  uniform  the  joint  at  the  bases  of  the  backing.  A  wheel 
should  never  be  u^ed  when  and  where  it  touches  any  point  save  the  one 
upon  Vvhich  we  desire  to  operate.  Flat  and  half-round  gravers  are 
employed  for  the  finishing,  dressing,  and  scraping.  The  tops  of  the 
joints  between  the  backings  are  given  a  uniform  concavity  by  means  of 
engine  burs  of  the  plug-finishing  variety.  The  backings  themselves  and 
the  plate  are  not  to  be  reduced  in  thickness  at  any  point,  for  this  reason 
tools  and  appliances  should  never  be  larger  than  necessary  to  remove 
the  superfluous  solder. 

Useful  points  for  the  smoothing  of  the  surfaces  of  the  backings  and 
their  joints  are  made  of  old  corundum  wheels  softened  by  heat  and  drawn 
out  into  flat  pencils.    By  altering  the  shapes  of  their  points  these  pen- 


628 


SWAGED  METALLIC  PLATES. 


cils  may  be  formed  so  that  they  may  be  operated  in  any  irregular  places. 
After  all  of  the  surfaces  have  been  dressed  smooth,  water-of-Ayr  stones 
are  used  with  water  and  finely  powdered  pumice  stone,  to  give  the  final 
dressing;  they  are  passed  over  every  portion  of  the  plate  surface,  oblit- 
erating all  of  the  tool-marks  and  removing  the  outer  coating  of  the  en- 
tire plate.  "To  prevent  the  entrance  of  foreign  particles  in  the  spaces 
between  the  teeth  and  plate,  and  between  the  teeth  themselves,  the  den- 
ture may  be  warmed,  and  melted  paraffin  flowed  into  all  interstices: 
this  is  permitted  to  remain,  as  it  effectually  prevents  the  collection  of 
debris  and  secretions  in  parts  inaccessible  to  ordinary  cleansing  agents" 
(Bonwill),  The  piece  is  now  transferred  to  the  polishing  lathe,  where 
the  smoothing  is  completed  by  means  of  fine  felt-wheels  and  powdered 
pumice. 

All  scratches  or  tool-marks  left  upon  backings  or  plate  by  the  corun- 
dum wheel  or  graver  in  levelhng  the  solder  and  platinum  pins  should  be 
removed,  first  by  the  Scotch  stone,^  and  then  by  a  felt  buff -wheel  armed 
with  fine  pumice  and  water.  Felt-wheels  or  cones  of  different  sizes, 
some  small  enough  to  enable  the  operator  to  reach  places  difficult  of  ac- 
cess, should  be  kept  ready  for  use.     The  case  is  held  with  the  fingers 

embracing  the  outside  of  the  teeth 
Fi«'  562  and  supporting  the  body  of  the  plate 

firmly,  so  that  no  uneven  pressure 
is  brought  to  bear  upon  the  latter. 
Plates  are  occasionally  bent  during 
the  finishing  operation  if  held  im- 
properly. The  piece  is  kept  con- 
stantly in  motion,  so  that  while  buff- 
ing there  shall  be  no  prolonged  con- 
tact of  the  wheel  at  any  point.  The 
wheels  as  they  are  worn  down  are 
preserved  for  buffing  small  spaces 
When  the  surfaces  of  the  plate  and 
backings  are  perfectly  smooth,  the 
edges  of  the  plate  rounded  and  freed 
of  all  minute  irregularities,  a  brush 
having  a  row  of  stiff  bristles  is  sub- 
stituted forthe  wheel  (Fig.  562) ;  this 
is  passed  rapidly  over  the  surfaces  of  plate  and  backings,  cleansing  well 
the  palatal  surface  of  the  former,  but  removing  none  of  its  fine  lines. 
When  all  the  surfaces  have  received  a  fair  polish  by  this  means,  a  sim- 
ilar brush  is  placed  on  the  mandrel,  and  they  are  further  surfaced,  using 
a  paste  of  chalk  as  the  polishing  medium.  Succeeding  this,  a  broad 
brush  having  fine  bristles  is  employed  with  the  chalk  paste,  to  give 
a  high  polish  to  all  of  the  surfaces — a  sufficient  finish  to  render  the  color 
of  the  solder  undistinguishable.  The  plate  is  from  time  to  time  washed 
to  observe  the  progress  of  these  operations,  and,  after  the  buffing  with 


Brush  wheel,  cup-shaped  for  surfacing. 


*   Otherwise  known  as  "water-of-Ayr"'  stone. 


REPAIRING  SOLDERED  DENTURES.  629 

chalk  and  soft  wheel,  is  scriibbetl  well  with  soap  to  free  it  from  all  par- 
ticles of  pumice  or  chalk. 

The  case  is  now  ready  for  the  final  polishing.  For  this,  a  brush 
wheel  four  inches  in  diameter,  having  the  softest  of  bristles,  is 
employed.  A  thin  mixture  is  made  of  alcohol  and  the  finest  jeweler's 
rouge  (an  oxide  of  iron) ;  this  is  painted  over  the  surfaces  of  the  denture, 
and  the  brush,  revolving  as  rapidly  as  possible,  is  passed  and  re- 
passed over  all  parts  until  the  metal  portions  of  the  denture  have  a  pol- 
'ish  equalling  that  of  the  inner  case  of  a  watch.  Every  trace  of  the  pol- 
ishing  powder  is  removed  with  soap  and  water. 

Any  rouge  remaining,  about  the  joints  which  is  not  removable  by 
soap  and  water,  may  be  destroyed  by  touching  the  joints  with  nitric  acid, 
then  re-applying  the  soap. 

SPIRAL  SPRINGS. 

Prior  to  the  advent  of  the  vacuum-chamber  plates,  the  retaining  ap- 
phance  employed  with  full  dentures  was  that  known  as  spiral  springs. 
Improvements  in  laboratory  technique,  comprised  in  better  means, 
methods,  and  materials  for  impression-taking,  together  with  a  more  ac- 
curate adaptation  of  plates,  have  so  limited  the  use  of  these  springs  as  to 
place  them  in  the  class  of  obsolete  appliances.  It  is  extremley  rare 
that  recourse  to  this  method  of  retention  is  ever  necessary.  Springs 
are  employed  only  when  the  anatomical  configuration  of  the  parts 
would  render  the  employment  of  other  retainig  devices  inapplicable. 

Examples  of  such  cases  are  found  when  any  of  the  following  condi- 
tions exist:  extreme  flatness  of  the  arch;  extreme  contraction  of  the 
area  upon  which  the  plate  rests;  an  exaggerated  softness  and  thickness 
of  the  soft  tissues  of  the  mouth ;  or  for  attachment  to  obturators  or  arti- 
ficial vela  in  edentulous  cleft-plate  cases,  and  prosthetic  devices  made 
necessary  by  surgical  operations. 

REPAIRING  SOLDERED  DENTURES. 

The  common  casualties  to  soldered  dentures  which  demand  repair 
are  cracks  of  the  plate,  fracture  of  one  or  more  teeth,  the  loss  of  a  nat- 
ural tooth,  leaving  a  gap  in  the  arch,  or  requiring  a  readjustment  of 
clasps. 

When  an  addition  of  plate  to  overlie  spaces  left  by  the  loss  of  a  natural 
tooth  or  teeth  is  required,  a  plaster  impression  is  taken  of  the  part 
with  the  denture  in  position  in  the  mouth. 

The  plate  is  to  be  withdrawn  in  the  impression.  A  wax-bite,  which 
has  also  been  taken  with  the  plate  in  the  mouth  and  before  taking  the 
impression,  is  mounted  and  an  articulation  made.  If  the  break  in  the 
outline  be  small  and  of  regulai"  form,  a  die  is  not  required  to  fit  the  ad- 
ditional pieces.  The  edges  of  the  plate  surrounding  the  break  are  to  be 
bevelled  from  the  palatal  side.  If  the  edges  of  the  break  be  more  than 
one-sixteenth  of  an  inch  from  contact  with  the  model,  a  series  of  saw- 


630  SWAGED  METALLIC  PLATES. 

cuts  are  made  along  it,  extending  into  the  plate  half  way  to  the  line  of 
contact  with  the  east.  A  thin  piece  of  metal  similar  to  that  of  the  den- 
ture is  made  to  conform  to  the  surface  of  the  model:  its  inner  edge  is  to 
come  within  the  plate  line  as  far  as  the  end  of  the  bevel,  its  outer  edge  to 
be  on  a  line  with  the  plate  line. 

A  joint  made  between  the  plate  and  the  supplementary  piece  is 
stronger  when  the  edges  of  the  plate  overlap  the  patch:  the  adaptation 
is  more  accurate,  and  to  secure  the  necessary  strength  it  is  not  re(juired 
to  leave  an  unsightly  protuberance.  The  leaflets  between  the  small 
saw-cuts  are  now  bent  down,  covering  the  added  piece.  The  tooth  or 
teeth  are  fitted  to  their  places,  and  backings  made.  The  several  pieces 
are  cemented  together,  and  the  fixture  is  invested;  to  prevent  the  invest- 
ment filling  the  joint  and  excluding  of  the  solder,  the  joint  is  covered 
with  thin  paper  or  filled  with  wax.  The  cement  is  picked  away,  the 
surfaces  well  covered  by  a  cream  of  borax,  and  in  the  space  between  the 
backings  and  the  plate  edge  surrounding  the  break  a  piece  of  plate  of 
No.  26  gauge  is  set,  fitting  the  piece  beneath  it.  Solder  is  placed  around 
the  joints  and  the  case  well  heated.  In  the  soldering  the  heat  is  to  be 
thrown  upon  the  plate  beyond\the  line  of  the  break,  so  that  the  solder 
may  be  drawn  beneath  the  plate  and  fill  the  joint.  The  deflected  heat 
usually  flows  the  solder  about  the  pins  of  the  teeth  and  at  the  base  of 
the  backing. 

Should  the  space  to  receive  the  addition  be  large  or  have  an  irregular 
form,  it  is  advisable  to  swage  the  piece.  The  plate  edges  adjoining  the 
open  space  are  to  be  bevelled,  and  the  line  of  the  edges  traced  on  the 
model  by  means  of  a  pin  point.  The  plate  is  removed  from  the  model, 
the  latter  is  varnished,  and  a  small  the  made  of  the  part  to  be  covered 
by  plate.  A  piece  of  plate  of  No.  26  gauge  is  swaged  to  fit,  and  its 
inner  edge  cut  down  until  it  is  slightly  broader  than  the  pin  scratch  on 
the  model.  Saw-cuts  are  made  in  the  plate  edges  surrounding  the 
break,  and  the  leaflets  bent  down,  holding  the  swaged  section.  The 
teeth  are  mounted  and  the  pieces  united  as  described. 

Occasionally  it  is  necessary  to  make  the  repair  in  two  operations.  It 
may  be  impossible  to  unite  perfectly  the  piece  to  the  plate  and  the  tooth 
to  both  in  one  soldering.  Such  cases  are  found  in  those  having  a  por- 
tion of  the  joint  between  the  supplementary  piece  and  the  plate  extend 
far  beyond  the  palatal  edge  of  the  artificial  tooth;  for  instance,  where  it 
is  required  to  add  an  extension  to  the  end  of  a  lower  plate,  the  additional 
piece  being  virtually  a  small  plate  covering  the  ridge.  In  such  cases 
the  piece  is  first  swaged,  fitted,  and  soldered  to  the  plate,  and  the  tooth 
or  teeth  mounted  in  a  second  operation. 

A  common  casualty,  as  noted  above,  is  a  crack  in  some  portion  of  the 
plate.  Such  breaks  are  to  be  repaired  by  the  addition  of  a  strip  of  plate, 
never  by  solder  alone.  The  case  is  cleansed  thoroughly  and  the  edges 
of  the  crack  are  brought  together.  Should  the  edges  of  the  crack  be 
separated  more  than  about  one-twentieth  of  an  inch,  it  is  inadvisable  to 
attempt  readjustment  of  the  edges:  the  repair  is  to  be  made  then  with 
out  anv  bending.     The  crack  is  filled  with  the  cream  borax.     When  this 


REPAIRING  SOLDERED  DENTURES.  631 

is  dry  the  plate  is  invested,  the  crack  being  just  covered  on  the  under 
side  with  thin  paper — wetted  so  as  to  remain  in  place  and  prevent  the 
investment  entering,  and  a  piece  of  plate  of  No.  2S  gauge,  about  a 
quarter  of  an  inch  wide  and  extending  the  full  length  of  the  crack,  is 
fitted  to  the  plate  over  the  crack.  Its  upper  edges  are  bevelled,  and 
it  is  well  cleansed,  and  the  surfaces  to  be  united  covered  by  the  flux.  A 
piece  of  solder  is  laid  at  each  edge,  and  the  case  is  heated  and  soldered : 
in  finishing,  the  strip  is  to  represent  a  rounded  ridge.  Should  the  crack 
be  at  the  portion  of  a  plate  embracing  the  neck  of  a  natural  tooth,  a 
semilunar  piece  is  to  be  fitted  over  the  plate  and  soldered  to  it. 

^Yhen  the  teeth  are  broken  from  a  denture  an  impression  is  taken 
with  the  plate  in  the  mouth,  an  articulation  made,  the  tooth  fitted, 
backed,  and  soldered  as  with  a  new  case. 

If  the  tooth  be  broken  away  from  its  backing  and  lost,  the  repair  may 
be  made  as  follows:  a  tooth  of  the  same  mold  and  color  is  selected, 
the  pin-holes  drilled,  not  punched,  as  the  latter  operation  invariably 
bends  the  backing.  The  tooth  is  ground  into  position:  this  operation 
will  require  some  care,  owing  to  the  pins  hampering  the  free  mobility 
of  the  tooth  in  its  space.     If  necessary,  the  pin-holes  may  be  reamed 

Fig.  563 


Riveting  hammer. 

out  and  made  larger.  If  there  be  any  marked  difference  in  the  situa- 
tions of  the  pins  of  the  new  tooth  from  those  in  the  old  one,  the  pin-holes 
are  sawn  into  elliptical  openings,  and  when  the  tooth  is  fitted  the  pins 
are  so  bent  as  to  cover  as  much  of  the  openings  as  possible.  The  case 
is  then  invested  and  soldered. 

Should  the  other  teeth  of  the  denture  be  of  such  type  as  would  be  en- 
dangered by  the  heating  necessary  in  soldering,  or  the  repair  be  hur- 
ried, it  is  advisable  to  rivet  the  tooth  to  the  backing.  A  tooth  is  selected 
having  the  pins  at  the  same  distance  apart  as  in  the  old  tooth.  The  pins 
of  the  old  tooth  are  carefully  drilled  out  of  the  backing,  and  holes  are 
countersunk  at  the  palatal  side.  The  tooth  is  fitted  to  position,  and 
a  folded  towel  is  laid  upon  an  old  counter-die,  the  tooth  to  be  riveted 
set  upon  the  towel,  and  no  other  tooth  should  press  hard  against  the 
latter :  repeated  light  blows  of  a  small  riveting  hammer  (Fig.  563)  are 
directed  against  the  ends  of  the  pins  until  each  is  forged  into  the  counter- 
sinks, filling  them  completely  and  leaving  rounded  heads,  which  are 
then  burnished  hard  to  complete  the  operation. 

Cases  will  occasionally  present  in  which  an  artificial  tooth  diflBcult  to 
replace  has  broken  away  from  its  backing,  leaving  pins  projecting  from 
the  back  of  the  tooth  about  one-fiftieth  of  an  inch  long.  Such  a  tooth 
is  to  be  boiled  in  a  test-tube  with  nitric  acid.     To  its  back  is  burnished 


032  SWAGED  METALLIC  PLATES. 

a  covering  of  platinum  plate,  No.  36  or  3S.  Apertures  are  made  over 
the  stumjxs  of  the  pins.  The  tooth  and  the  platinum  back  are  invested, 
a  piece  of  pure  gold  is  placed  over  each  pin,  and  the  platinum  is  soldered 
to  the  pins.  Tlie  old  pins  are  drilled  out  of  the  backing  standing  on  the 
plate.  The  back  of  the  backing  is  scraped  to  cleanse  and  thin  it,  and  its 
top  bent  inv^^ard  slightl).  The  tooth  with  the  platinum  back  is  set 
against  the  backing  and  cemented  to  it:  the  case  is  invested,  and  the 
platinum  soldered  to  the  backing,  using  a  low^-carat  solder. 

In  re])airing  cases  having  a  gum  of  one  of  the  vegetable  bases,  if  the 
backing  be  standing,  the  following  method  is  frequently  applicable:  the 
rubber  or  celluloid  is  cut  out  to  receive  the  neck  of  the  tooth,  but  the 
festoon  covering  the  latter  is  to  remain  untouched.  A  plain  tooth  is 
fitted  to  the  backing,  in  which  pin-holes  have  been  drilled  and  counter- 
sunk. Phosphate  of  zinc  colored  pink  with  carmine  is  placed  in  the  de- 
pression cut  in  the  gum,  and  the  tooth  pressed  into  position:  when 
the  cement  has  set,  the  pins  of  the  tooth  are  riveted  as  described. 

To  adjust  broken  or  detached  clasps  properly  it  is  recessary  to  take 
an  impression  of  the  clasp  tooth  with  the  plate  in  the  mouth.  Should 
the  clasp  itself  be  broken  it  is  better  to  make  a  new  one;  the  added  j)late 
and  solder  necessary  to  make  it  strong  will,  in  most  cases  destroy  its 
elasticity  and  impair  its  usefulness.  Now  and  again  a  gold  solder, 
lower  fusing  than  the  standard  grade  is  required  for  repair  work.  Low 
grade  gold  solders  should  be  sparingly  used,  as  once  used  on  a  denture 
their  use  must  be  continued;  the  attempt  to  use  solder  of  a  higher 
grade  afterward  is  attended  with  serious  risk,  owing  to  the  reflowing  of 
the  inferior  solder. 

For  this  purpose  the  following  fonnulas  will  suffice: 

Sixteen  carat  CJold  Solder. 
16  parts    pure  gold, 
5       "  "     silver, 

2       "  "     copper, 

1^     "  "      zinc. 

Fourteen  carat  Gold  Solder. 
14  parts    pure  gold, 
6     "  "     silver, 

3     "  '      copper, 

IJ-     "  "      zinc. 

A  lower  grade  than  fourteen  carat  is  inadmissible  for  dental  work. 
These  solders  may  be  made  more  fusible  by  increasing  the  amount  of 
zinc  without  reducing  the  fineness,  and  are  so  made  for  jewelers  use. 
They  are  safe  only  in  cases  where  the  point  to  be  soldered  is  alone  highly 
heated,  and  where  the  work  can  be  quickly  done.  This  is  not  the 
case  in  the  dental  workroom.  As  soldering  must  be  done  by  a  dental 
mechanic,  such  solders  quickly  run  through  the  plate,  producing  an  in- 
jury difficult  to  repair. 

A  method  of  repairing  metallic  plates  without  subjecting  the  denture 
to  the  soldering  operation,  and,  what  may  be  more  important,  a  means 
of  attaching  a  clasp  or  an  additional  tooth  to  a  plate  without  depriving 
the  patient  of  the  piece  except  for  a  few  minutes,  has  been  devised  by 
Dr.  Charles  J.  Essig. 


REPAIRING  SOLDERED  DENTURES. 


633 


A  typical  application  of  the  method  will  illustrate  its  advantages: 
A  patient  is  wearing  a  partial  gold  plate;  one  of  the  remaining  natural 
teeth  is  becoming  progressively  looser,  and  may  be  lost  at  any  time;  it 
is  not  permissible  to  deprive  the  patient  of  the  piece  for  the  length  of  tiem 
necessary  to  repair  it  by  soldering.  A  bite  and  impression  are  taken 
with  the  artificial  denture  in  position.  If  the  operation  be  the  prepara- 
tion of  an  artificial  tooth  to  be  substituted  for  a  loosening  natural  organ, 


Fig,  564 


Fig.  505 


Supplemental  plate  with  tooth  attached  ready 
to  be  riveted  to  a  denture.  Used  when  it  is  de- 
sired to  avoid  the  risk  of  soldering  in  repairing 
or  adding  to  a  denture. 


Supplemental  plate  with  clasp  attached 
ready  to  be  riveted  in  place.  Used  when 
it  is  desired  to  add  a  clasp  to  a  denture 
and  avoid  the  risk  of  soldering. 


as  soon  as  it  is  removed,  the  plaster  tooth  on  the  model  is  cut  away,  to- 
gether with  an  amount  of  plaster  to  represent  the  condition  of  the  soft 
parts  after  extraction.  A  die  and  counter-die  are  made,  and  a  piece  of 
plate  No.  26  is  swaged  which  shall  overlap  the  plate  as  shown  on  the 


Fig.  566 


Fig.  568 


Front  view  of  a  supple- 
mental plate  with  dowel 
ready  to  be  riveted  to  ^i 
denture.  Used  whi  u  i. 
is  desired  to  add  a  n  il- 
ural  tooth  to  a  deniiin' 
and  avoid  the  risk  of 
soldering 

Fig.  667 


Side  view  of  the  s  une 


Front  view  of  the 
same  with  the  natural 
tooth  cemented  onto 
the  dowel. 


Side  view  of  the  same. 


model,  for  one-fourth  of  an  inch  or  more :  a  tongue  to  extend  into  the 
interdental  space  is  to  furnish  a  support  to  the  artificial  tooth.  An  ar- 
ticulating model  is  made,  a  tooth  fitted  to  the  model,  and  a  backing 
adapted  to  it.  The  pieces  are  now  invested  and  united  by  means  of  sol- 
der, then  finished.  The  edges  of  the  plate  piece  should  receive  a  bevel, 
so  that  there  shall  be  no  abrupt  line  between  the  new  and  old  plate. 

To  add  a  clasp,  an  impression  is  taken  with  the  plate  in  position,  and 
a  model  is  made  which  shall  have  a  perfect  representation  of  the  tooth  to 
be  clasped.  The  clasp  is  fitted  to  the  tooth,  and  a  piece  of  plate  to  the 
general  plate,  as  described  above.  This  is  filed  away  about  the  base  of 
the  clasp  tooth  until  it  has  a  close  joint  with  the  clasp,  to  which  it  is  cem- 
ented, invested,  and  soldered,  and  finished  as  described. 


634  SWAGED   METALLIC  PLATES. 

To  add  these  pieces  to  the  i)late,  three  holes  are  drihed  through  the 
phite  as  marked  in  Fig.  564,  and  eaeli  is  countersunk  ui)oii  its  upper 
side.  When,  in  the  first  instance  noted,  the  natural  tooth  is  lost,  or,  in 
the  second,  the  clasp  addition  is  prepared,  the  piece  is  placed  in  the 
mouth  with  the  plate  itself  in  position,  and  by  means  of  a  sharp  excavator 
point  the  outlines  of  the  supplementary  piece  are  scratched  on  the  plate 
proper.  With  the  pieces  held  in  close  apposition  a  drill  is  placed  through 
the  openings  made  in  the  small  plate,  and  the  plate  proper  perforated : 
the  holes  are  countersunk  at  the  palatal  surface.  Gold  pins  upon  which 
rivet  heads  have  been  formed  are  placed  through  the  openings  and 
riveted,  thus  holding  the  sections  firmly  together. 

It  is  at  times  preferable  to  add  the  natural  tooth  to  the  plate  if  it  be 
one  of  the  incisors  or  canines,  and  is  free  from  caries.  An  impression 
is  taken  with  the  artificial  denture  in  position,  wdiich  need  include  only 
that  part  of  the  plate  to  which  the  attachment  is  to  be  made  and  the 
natural  teeth  immediately  adjoining  the  loose  organ.  A  supplemental 
plate  of  No.  26  guage  is  swaged,  to  which  is  soldered  a  stout  platinum 
gold  pin  of  about  No.  16  of  the  standard  gauge  (Figs.  566  and  567). 
The  plate  is  then  riveted  to  the  artificial  dentures,  the  root  of  the  nat- 
ural tooth  is  cut  ofi'  sufficiently  to  maintain  the  relative  height,  and  the 
pulp  canal  is  enlarged  by  means  of  a  fissure  drill  so  as  to  receive  the  gold 
pin.  When  the  tooth  has  been  carefully  fitted,  it  may  be  permanently 
fastened  to  the  plate  (Figs.  568  and  569)  by  means  of  oxyphosphate 
cement. 


CHAPTER     XV. 

COXTIXI-QUS-GUM   DENTURES. 
By  D.  O.  M.  LeCrox,M.D.,D.D.S. 

If  it  be  agreed  that  besitle  the  restoration  of  function,  one  of  the  chief 
desiderata  in  the  construction  of  an  artificial  denture  is  the  imitation 
of  the  natural  appearance  of  the  teeth  and  gums,  then  it  may  be  said 
that  the  continuous-gum  process  offers  greater  aesthetic  possibilities 
than  those  of  any  other  method  of  prosthetic  restoration.  By  its  means 
the  physical  characteristics  relating  to  the  appearance  of  the  restored 
tissues  may  be  so  closely  imitated  as  to  defy  detection  at  the  hands  of 
the  most  skilled  observers. 

Continuous-gum  takes  its  name  from  the  fact  that  when  the  porcelain 
used  for  this  purpose  is  fused  upon  a  platinum  base  to  which  specially 
designed  teeth  have  been  attached,  a  porcelain  surface  is  obtained 
which  is  without  break  in  continuity  between  teeth  and  gums. 

The  first  conception  of  the  uniting  of  porcelain  teeth  to  a  metallic 
base  by  means  of  a  fusible  porcelain  material  originated  in  Francs. 
Among  the  names  of  those  who  first  bent  their  eft'orts  in  this  direction, 
may  be  mentioned  INI.  Delabarre,  of  Paris,  who  in  1S20  used  a  material 
closely  resemblirig  ordinary  porcelain  tooth-body  to  unite  the  teeth  to 
the  plate.  Contemporaneous  vrith  that  of  this  pioneer,  we  find  the 
names  of  'M.  de  Fouze,  who  applied  jeweler's  enamel  for  the  purpose  of 
restoring  the  contour  of  the  gums,  and  of  'SI.  de  Chemant,  to  whom 
patents  were  granted  for  the  manufacture  of  a  form  of  denture  belong- 
ing to  this  type.  The  work  of  these  early  experimenters  was  attended 
ina  large  measure  ^-ith  failure  because  of  the  imperfect  character  of 
their  materials  and  the  lack  of  knowledge  concerning  the  means  for  their 
proper  fusing.  Experiments  vnxh  the  silicious  compounds  were  aban- 
doned before  any  satisfactory  results  were  obtained.  This  was  because 
of  the  great  heat  necessary  to  work  the  materials  used,  for,  according  to 
Dr.  Locke,  they  required  a  temperature  of  3761°  F.  for  proper  fusing. 

It  remained'  for  an  American  to  realize  the  object  sought  by  these 
early  French  investigators,  and  by  practical  researches  to  rescue  from 
obscurity  this  beauti'ful  process  and  place  it  before  the  dental  profes- 
sion upon  a  practial  working  basis.  It  was  Dr.  John  Allen,  of  New  York 
City,  who  in  1846  perfected  a  method  of  construction  and  compoim- 
ded  a  porcelain  body  upon  which  he  was  granted  patents  in  1S51. 
The  priority  of  this  invention  was  contested  by  Dr.  William  Hunter  in 
a  suit,  accounts  of  which  were  published  in  the  dental  journals  of  that 
time.  Dr.  Allen  surrendered  his  patents  of  ISol  because  of  defects  in 
them,  and  in  1856,  a  new  patent  was  issued  to  him  for  the  process  a^  he 
had  then  improved  it.     This  was  known  as  "Allen's  Continuous-Gum." 

635 


636  COXTINUOUS-GUM  DENTURES. 

Believing  in  the  po.s.sil)ilitie.s  which  this  process  offered,  a  few  men 
liave  worked  steadily  since  that  time  to  improve  and  develop  its  details, 
and  gradually  many  of  the  early  sonrces  of  anno}ance  and  failure,  such 
as  springing  of  the  plate,  and  checking  and  scaling  of  the  porcelain,  have 
been  overcome.  The  porcelain  bodies  now  manufactured,  are,  if 
properly  manipulated  and  fused,  sufficiently  strong  to  withstand  any 
legitimate  use.  It  is  essential,  however,  that  the  porcelain  should 
be  superposed  upon  a  metal  frame-work  constructed  with  strict 
regard  to  mechanical  principles.  Continuous-gum  body  of  to-day  is 
a  silicious  compound,  similar  in  composition  to  that  of  which  artificial 
teeth  are  made  except  that  it  is  more  fusible,  its  fusing  point  being 
2300°  F. 

Platinum  and  iridio-platinum  are  used  as  the  bases,  and  we  find  the 
tissues  underlying  them  to  maintain  a  condition  more  closely  approx- 
imating the  normal  than  under  the  vegetable  bases. 

The  objections  formerly  urged  against  this  variety  of  artificial 
denture,  viz.,  its  great  weight  and  the  dangers  and  difficidties  in 
the  baking  of  the  porcelain,  have  been  removed  to  a  large  extent  by  im- 
proved methods  of  construction. 

The  first  objection  as  to  weight  may  be  overcome  in  a  large  measure 
by  using  the  lighter  gauges  for  the  platinum  base.  The  writer  has  for 
a  number  of  years  used  Xos.  32  to  36  plate  (B  &  S  gauge)  for  upper 
dentures  with  most  satisfactory  results. 

The  use  of  modern  electric  furnaces  effectually  discounts  any  ob- 
jections on  the  score  of  baking  per  se,  for  these  appliances  are  thor- 
oughly satisfactory  in  convenience  of  operation  and  efficiency.  The 
consideration  of  the  warping  of  the  plate,  the  shrinking,  flaking,  under 
and  over-fusing  of  the  porcelain — accidents  possil^le  in  the  process  of 
baking  and  urged  by  some  as  ol>jections  to  the  method,  will  be  discussed 
at  the  appropriate  place  in  this  chapter. 

As  a  minor  objection  may  be  mentioned  the  liability  of  fracture 
of  the  plate.  Proper  admonition  to  the  patient  as  to  the  care  of  the 
denture  should  always  be  given,  and  by  the  exercise  of  due  caution  in 
cleansing  the  piece,  any  annoyance  on  this  score  may  be  avoided. 
Fracture  in  the  mouth  is  of  rare  occurence. 

The  tissues  of  the  mouth  react  more  kindly  to  the  presence  of  a 
platinum  base-plate  than  they  do  to  any  of  the  vegetable  bases.  All  the 
materials  of  which  the  denture  is  composed  being  good  conductors,  the 
thermal  variations  are  readily  communicated  to  all  the  underl\'ing 
parts.  From  a  hygienic  standpoint,  the  platino-porcelain  plate  stands 
alone.  There  are  no  interstices  to  catch  food  debris,  and  as  the  denture 
is  absolutely  uninfluenced  by  the  secretions  of  the  mouth,  or  the  pro- 
ducts of  bacterial  action,  it  may  be  made  as  clean  and  fresh  as  new  by 
ordinary  cleansing  methods  which  may  be  instituted  by  the  patient. 
One  of  the  chief  points  of  excellence  in  favor  of  the  continuous-gum 
method  is  the  facility  and  accuracy  with  which  the  natural  organs  are 
imitated.  Any  loss  of  gum  or  palatal  contour  may  be  so  faithfully 
reproduced  in  form  and  color  as  to  defy  detection. 


JMPBESSIONS  AND   CASTS.  637 

Continuous-gum  dentures  are  applicable  with  most  satisfactory 
results  in  full  cases,  upper  and  lower,  but  it  is  quite  possible  to  employ 
them  with  good  effect  in  many  cases  requiring  partial  dentures. 

IMPRESSIONS  AND  CASTS. 

The  first  requisite  for  success  in  constructing  continuous-gum  den- 
tures is  a  good  impression,  and  for  this  purpose  plaster  of  Paris  is 
the  material  par  excellence.  The  manner  of  taking  the  impression  and 
its  subsequent  treatment  are  described  in  detail  in  another  section  of 
this  work.     The  cast  is  obtained  and  dies  and  counter-dies  made  as  for 

Fig.  570 


Showing  form  of  arch  where  chamber  may  not  be  necessary. 


other  varieties  of  metal  dentures.  The  indications  which  govern  the 
use  of  vacuum-chambers  are  the  same  as  for  other  metal  plates.  If  in 
the  judgment  of  the  operator  a  vacuum-chamber  is  indicated,  it  may  be 
carved  in  the  impression  thus  forming  an  integral  part  of  the  cast  or 
it  may  be  placed  upon  the  cast  after  the  latter  has  been  removed  from 
the  impression  in  any  of    the  ways    described    in    Chapter    XI.     In 

Fig.  571 


Cast  of  the  upijer  jaw  with  ledge  for  turning  the  rim. 


cases  presenting  well  defined  alveolar  ridges  and  moderately  deep 
vaults  the  vacuum-chamber  is  unnecessary.  The  firmness  of  the  ad- 
hesion of  the  plate  to  the  underlying  tissues  depends  upon  the  accuracy 
of  its  adaptation  to  them.     If  this  is  perfect  it  v^^ill  adhere  with  sufficient 


63S  CONTINUOUS-GUM  DENTURES. 

tenacity,  but  if  the  plate  is  poorly  adapted  or  warped  in  any  degree,  the 
stability  of  its  retention  is  thereby  lessened  proportionately.  If  it  is 
intended  to  swage  a  rim  to  the  plate,  especial  care  must  be  exercised  in 
marking  the  outline  of  the  latter  on  the  cast.  It  should  follow  such  a 
line  as  will  prevent  any  possibility  of  its  impingement  upon  the  muscles 
of  the  lips  and  checks  or  other  movable  tissues.  If  after  the  piece  is 
finished  such  impingement  does  exist,  the  beauty  and  finish  of  the  plate 
would  be  seriously  marred  by  trimming.  A  layer  of  wax  slightly  thicker 
than  the  proposed  rim  is  adapted  to  the  cast,  following  accurately  the 
plate  outline.  It  should  form  with  the  wall  of  the  cast  an  angle,  the  de- 
gree of  which  should  not  be  so  acute  as  to  interfere  with  accurate  mold- 
ing. The  wax  is  then  trimmed  away  to  blend  gradually  with  the  sides 
of  the  cast.  The  cast  thus  prepared  is  now  to  have  the  necessary 
varnish  applied  and  the  die  is  obtained  in  the  usual  way. 

Results  obtained  with  dies  made  of  nickel  Bal)bitt  metal,  or 
Babbitt  metal  of  Haskell's  formula,  will  be  found  satisfactory  in  this 
work.  The  latter  alloy  contracts  less  than  zinc,  and  plates  made  over 
dies  composed  of  it  fit  the  plaster  cast  as  they  do  the  die. 

FORMING  THE  FULL  UPPER  PLATE. 

The  pattern  of  the  plate  in  heavy  tin  foil  is  reproduced  in  pure 
platinum  No.  32  to  36  gauge  for  upper  plates,  the  thickness  of  the 
platinum  depending  upon  the  form  and  size  of  the  plate.  The  writer 
has  used  all  gauges  and  finds  plate  of  these  numbers,  properly  rein- 
forced to  meet  the  individual  requirements,  not  only  sufficiently 
rigid  for  all  purposes,  but  contributing  much  to  the  lightness  of  the 
completed  denture. 

The  face  of  the  die  is  covered  with  a  thin  piece  of  wet  muslin,  and 
the  platinum  after  being  well  annealed  by  placing  the  platinum  in  the 
electric  furnace,  bringing  it  to  a  white  heat,  and  allowing  it  to  cool 
slowly,  is  a.dapted  as  closely  as  possible  to  the  palatal  \'ault  by  pressure 
applied  with  the  thumbs,  and  by  the  use  of  the  horn  mallet.  Great 
care  must  be  observed  while  annealing  the  platinum  that  no  particles 
of  zinc  or  lead  are  attached  to  it,  for  they  would  become  alloyed  with  it, 
thus  producing  a  hole  in  subsequent  heatings,  or  causing  the  plate 
to  crack  or  break  in  swaging,  or  possibly  subsequently  discoloring  the 
porcelain  paste.  Using  muslin  over  the  face  of  the  die,  and  pickling 
the  piece  each  time  before  it  is  annealed  to  remove  any  possible  trace 
of  base  metal  will  effectually  prevent  this.  The  process  of  swaging 
is  continued,  reannealing  the  platinum  whenever  its  returning  obduracy 
necessitates,  until  a  fairly  close  approximation  to  the  ^•ault  is  obtained. 
A  partial  counter-die  made  of  good  modelling  composition  may  now  be 
used.  The  composition  is  softened  and  molded  to  the  vault  of  the  plate, 
completely  filling  the  latter.  It  is  then  hardened  by  dipping  into  cold 
water.  The  composition  is  now  placed  in  position  on  the  plate  which 
is  in  place  on  the  die,  and  the  whole  is  clamped  securely  to  the  bench  with 


FORMING   THE  FULL    UPPER  PLATE.  639 

an  ordinary  bench  clamp,  one  arm  of  the  clamp  engaging  the  under  sur- 
face of  the  bench,  the  upper  arm  engaging  the  composition.  In  this 
manner  the  plate  is  held  securely  in  position  on  the  die  while  its  alveolar 
borders  are  adapted  with  the  swaging  mallet. 

The  soft  platinum  exhibits  a  tendency  to  wrinkle  and  tear  under 
manipulation,  so  that  all  undue  haste  and  force  are  to  be  avoided.  If, 
however,  the  metal  should  be  torn,  small  breaks  in  its  continuity  may 
be  repaired  by  soldering  a  piece  of  thin  platinum ,  gauge  36,  over  the  hole 
with  platinum  solder. 

When  the  adaptation  to  the  die  is  as  accurate  as  can  be  obtained  by 
pressure  and  the  mallet,  the  plate  is  trimmed  approximately  to  the  line 
marked  on  the  cast.  It  is  now  ready  for  the  counter-die,  and  extreme 
care  should  be  observed  to  prevent  contact  of  the  platinum  with  the 
base  metal  of  the  counter-die,  particularly  if  the  latter  be  made  of  lead 
or  an  alloy  containing  that  metal.  As  is  well-known,  lead  and  platinum 
combine  with  remarkable  ease,  and  should  small  particles  of  lead 
become  attached  to  the  platinum  when  the  latter  is  heated,  the  base 
metal  forms  an  alloy  with  that  part  of  the  platinum  with  which  it  is  in 
contact.  This  alloy  is  very  fusible,  and  if  the  plate  is  not  at  once  per- 
forated, the  part  so  contaminated  will  always  be  liable  to  this  accident 
upon  subsequent  heatings.  To  avoid  any  such  contingency  it  is  well 
to  interpose  betweeen  the  surfaces  of  the  counter-die  and  plate,  wet 
muslin  or  thin  rubber  dam.  This  will  also  assist  in  disengaging  the 
plate  from  the  counter-die  if,  as  frequently  happens,  it  becomes  wedged 
therein  from  the  force  of  the  swaging.  Should  the  platinum  become 
contaminated  with  the  base  metals,  it  must  be  pickled  in  hot  nitric  acid 
before  further  annealing. 

The  plate  is  at  first  lightly  swaged  between  die  and  counter-die,  then 
removed  and  examined  carefully  for  wrinkling  or  breaks.  Should 
wrinkles  develop  they  should  be  corrected  with  pliers  and  the  horn  mal- 
let. The  swaging  should  alternate  with  pickling  and  annealing  until 
the  adaptation  is  perfect.  The  plate  is  then  closely  trimmed  to  the 
plate  outline,  leaving  an  excess  sufficient  for  the  rim  if  this  is  to  be 
turned,  and  it  is  ready  to  be  tried  in  the  mouth.  The  rim  is  to  be  com- 
pletely turned  after  the  first  coat  of  body  has  been  baked. 

The  operator  may  prefer  to  solder  a  wire  along  the  alveolar  border 
of  the  plate  instead  of  turning  the  rim,  in  which  event  the  plate  is  to  be 
trimmed  to  its  true  dimensions  which  are  determined  by  trial  in  the 
mouth.  The  wire  rim  permits  a  trimming  of  the  plate  margins  after  the 
body  has  been  applied  and  even  after  the  plate  has  been  worn.  The 
vacuum-chamber  in  a  continuous-gum  denture  is  preferably  formed 
in  the  plate  itself,  although  it  may  be  cut  and  soldered  using  for  the 
chamber  cap  a  piece  of  plate  of  the  same  thickness  and  soldering 
it  in  with  25  per  cent,  platinum  solder.  This  is  the  solder  em- 
ployed to  best  advantage  in  continuous-gum  work.  The  relative 
position  of  the  pieces  united  by  it  will  not  change  in  the  intense  heat 
of  the  furnace.  Pure  gold  may  be  used  if  the  pieces  are  in  absolute 
contact  and  a  minimum  amount  of  solder  used,  but  an  excess  of  gold 
should  be  avoided,  as  it  is  thoroughly  melted  and  widely  diffused  by 


640 


COyTINUO  US-G  UM  DENTURES. 


the  hifh  temperature  at  which  porcelain  fuses.      Solders  containing 
base  metals  siiould  never  be  used. 

Strengthening  Pieces.  — The  object  of  these  is  to  add  strength  to  the 
parts  of  tlie  plate  which  are  liable  to  undergo  alteration  in  form,  either 
when  it  is  subjected  to  the  great  heat  of  the  furnace,  or  under 
the  stress  of  mastication.  Those  places  in  which  experience  has 
demonstrated  the  necessity  of  additional  strength  are  the  posterior  Iwr- 
der  of  the  plate,  usually  i-eferred  to  as  the  heel,  and  that  portion  of  the 
plate  extending  posteriorly  for  a  small  distance  from  the  alveolar  bor- 
der along  the  median  line. 

The  form  these  strengthening  pieces  should  take  is  governed  by  the 
judgment  of  the  operator.  The  method  of  forming  and  adjusting  them 
employed  by  the  writer  is  as  follows:  patterns  of  heavy  tin-foil  are  pre- 
pared; the  pattern  for  the  anterior  piece  is  cut  roughly  to  the  form  of  a 
triangle,  the  base  slightly  overlapping  the  ridge  anteriorly;  the  apex  ex- 
tending l)ack  toward  the  vault  of  the 
plate  and  lying  on  the  median  line,  the 
size  to  be  governed  by  the  size  of  the 
plate.  (Fig.  572.)  This  pattern  is  to 
be  reprofluced  in  iridio-platinum  plate, 
No.  24  to  26  gauge,  according  to  the 
case.  The  piece  is  well  annealed, 
adapted  to  the  die  with  the  mallet  and 
then  swaged  between  the  die  and 
counter-die.  It  is  now  placed  in  posi- 
tion on  the  plate  and  both  are  swaged 
together. 

The  posterior  pattern  is  cut  in  the 
form  of  a  strip  three-sixteenths  of  an 
inch  wide,  extending  across  the  entire 
posterior  border  of  the  plate.  This  pat- 
tern is  also  reproduced  in  iridio-plati- 
num No.  24  or  26  gauge.  It  should 
be  observed  that  the  object  of  this  piece 
is  two-fold;  first,  to  give  additional 
strength  to  the  heel  of  the  plate;  sec- 
ond, to  engage  the  porcelain  and  give 
finish  to  this  part  of  the  plate.  In  or- 
der to  serve  best  this  double  purpose,  the  strip  should  be  so  formed  that 
when  finally  adjusted  its  anterior  edge  is  distinctly  raised,  while  the 
posterior  two-thirds  of  the  body  of  the  strip  lie  in  close  apposition  to 
the  plate.  To  accomplish  this  result  a  strip  of  brass  is  swaged  to  con- 
form to  the  portion  of  })late  immediately  in  front  of  and  covered  by  the 
anterior  Iwrder  of  the  iridio-platinum  piece  when  the  latter  is  in  jM)si- 
tion.  The  posterior  border  of  the  brass  strip  should  be  filed  to  a  feather 
edge.  The  strengthening  piece,  having  been  adjusted  to  the  die  and 
swaged  in  the  usual  manner,  is  now  placed  in  position  on  the  plate  with 
the  brass  strip  ])roperly  interposed,  and  the  pieces  are  swaged  together 


Reinforcing  pieces  for  full  upper  denture. 


ARTICULATION.  643 

the  !)akiii<>-  of  the  body  reduces  the  contraction,  and  maintains  the  con- 
tours in  these  regions.  When  the  rerjuirements  of  the  case  cull  for  very 
short  teeth,  those  employed  in  vulcanite  or  celluloid  work  may  he  used 
Any  artistic  skill  which  the  operator  may  possess  has  wide  latitude 
for  its  display  in  the  arrangement  of  the  teeth.  The  varying  facial  ex- 
pressions of  tiie  patient  are  studied  closely  and  the  endeavor  is  made 
to  fix  in  the  mind  the  natural  expression  both  in  repose  and  when  the 
face  is  animated  as  in  the  acts  of  talking  and  laughing.  Not  only- 
must  an  accurate  knowledge  of  all  the  elements  entering  into  and  con- 
'stituting  what  is  known  as  the  natural  expression  be  borne  in  mind, 
but  what  is  as  equally  important  from  a  less  aesthetic  standpoint,  a 
thorough  knowledge  of  the  mechanical  principles  involved  in  the  reten- 
tion of  the  denture.  A  just  consideration  of  these  observations  leads  to 
the  further  statement  that  in  the  construction  of  an  artificial  denture, 
the  process  is  often  attended  by  a  series  of  compromises  by  which  the 

Fig.  574 


Set  of  continuous-gum  teeth. 

various  aesthetic  features  are  reconciled  to  the  practical  requirements. 
Therefore,  a  comprehensive  knowledge  of  all  these  factors  will  best 
place  one  in  a  position  to  so  adjust  the  conflicting  interests  that  the  fin- 
ished product  will  not  suffer. 

The  central  incisors  are  usually  arranged  first.  Each  tooth  is  ground 
to  rest  directly  on  the  plate,  and  the  pin  should  come  in  perfect  contact 
with  the  wire  on  the  top  of  the  alveolar  ridge  presently  to  be  described, 
or  with  the  plate,  in  order  to  hold  the  tooth  in  position  during  the  pro- 
cess of  fusing  the  porcelain.  Between  each  tooth  and  the  platinum 
base  there  should  always  be  two  points  of  contact,  viz :  the  platinum  pin 
and  the  porcelain  root;  the  teeth  will  then  be  less  liable  to  change  their 
position  by  the  shrinkage  of  the  porcelain.  If  the  length  of  the  roots  is 
not  sufficient  to  enable  them  to  touch  the  plate,  it  will  be  necessary  to 
support  them  in  position  by  interposing  little  pieces  of  broken  porcelain 
teeth. 

Slight  irregularities  of  alignment  commonly  found  in  the  natural  teeth 


644 


coxTTXT^n  rs-o  um  dentures. 


are  easily  reprorliiced  and  materially  aid  in  giving  a  natural  appear- 
ance to  the  case. 

There  are  often  conditions  of  the  remaining  natural  teeth  resulting 
from  decay  and  organic  discoloration,  which  make  it  impossible  to  find 
in  the  stock  of  the  manufacturers  a  desirable  match  for  a  partial  den- 
ture. Such  needs  of  the  operator  can  only  be  met  by  selecting  a 
porcelain  tooth,  the  body  of  which  is  the  same  general  color  as  the 
natural  teeth  to  be  matched  and  treating  it  with  mineral  colors  in 
imitation  of  the  natural  organs. 

After  the  arrangement  is  completed  in  conformity  with  the  ideas  of 
the  operator,  the  teeth   are  attached  to  the  plate  with  adhesive   wax. 

Fio.  57.3 


Iia.-('-iilat<>  with  Teeth  arraiijie'l  uiion  it. 

Wax  is  also  loosely  molded  over  the  l)uccal  and  labial  walls  of  the  plate 
to  approximate  the  natural  contours. 

The  piece  is  now  transferred  to  the  mouth,  the  articulation  noted 
and  any  slight  corrections  or  alterations  made.  I'he  amount  of  wax 
necessary  to  restore  the  contours  is  also  to  be  noted;  this  serves  as  a 
guide  in  the  application  of  the  body. 

The  next  step  is  the  adjustment  of  the  iridio-platinum  wire  around 
the  crest  of  the  ridge,  which  serves  for  the  attachment  of  the  pins  and 
also  gives  additional  strength  to  the  plate.  The  writer  advocates  the 
use  of  Xo.  10  iridio-platinum  round  wire  instead  of  the  platinum  strips 


Fig.   570 


Clamp  for  holding  reinforcing  pieces  on  plate  during  soldering. 

which  are  sometimes  employed.     The  porcelain   adapts    itself    more 
uniformly  to  the  wire  and  fuses  with  less  tendency  to  crack. 

In  determining  the  proper  position  for  the  wire,  the  plate  is  placed 
on  the  cast,  and  a  wall  of  soft  modelling  composition  is  adapted  to  cover 
the  anterior  and  lateral  walls  of  the  cast  and  all  exposed  portions  of  the 
teeth,  and  extending  from  the  la.st  molar  on  one  side  to  the  same  tooth 
on  the  other.  The  composition  is  hardened  and  the  wax  removed  thus 
freeing  the  pins  which  are  bent  slightly  upward.     The  wire  is  adjusted 


INVESTING.  645 

under  the  pins  and  waxed  to  the  plate.  The  teeth  should  then  be  re- 
moved en  masse  with  the  composition.  The  wire  is  now  held  in  posi- 
tion on  the  plate  with  clamps  like  that  shown  in  Fig.  576  and  soldered. 
The  modelling  composition  wall  containing  the  teeth  is  then  returned 
to  the  plate  in  position  on  the  cast,  the  pins  bent  down  in  contact  with 
the  wire,  and  securely  attached  with  adhesive  wax.  The  composition 
wall  may  then  be  softened  by  dry  heat  and  removed ,  taking  care  that  the 
wax  about  the  pins  is  not  melted  and  that  the  relation  of  the  teeth  to 
the  plate  is  undisturbed.  A  plaster  wall  may  be  used  instead  of  the  one 
described.  After  the  teeth  are  attached  to  the  plate,  the  case  is  ready 
for  the  investment. 

INVESTING. 

The  investment  best  adapted  for  continuous-gum  work  is  composed 
of  fine  asbestos,  one-sixth;  coarse  calcined  silex,  one-half;  plaster  of 
Paris,  one-third. 

The  investment  best  adapted  for  continuous-gum  work  is  composed 
ciently  plastic  to  flow  freely  between  and  around  the  teeth.  All  surfaces 
of  the  teeth  to  be  embraced  in  the  investment  should  receive  a  coating 
of  thick  shellac  varnish.  This  is  to  prevent  the  fusing  of  the  investment 
with  the  porcelain  teeth  during  the  soldering,  an  accident  which  is  likely 
to  occur  at  the  high  temperature  required  to  fuse  platinum  solder. 
The  shellac  burns  out  when  the  plate  is  heated  up  and  leaves  a  small 
space  about  the  teeth. 

To  make  the  investment  small,  uniform  in  thickness,  and  compact, 
a  matrix  into  which  it  may  be  cast,  is  formed  by  placing  the  plate  with 
teeth  attached  upon  a  flat  surface  like  the  work  bench,  the  occlusal 
surface  of  the  teeth  being  uppermost.  Then  a  strip  of  base-plate  wax 
is  bent  into  the  form  of  a  ring,  w^hich  shall  surround  the  plate,  follow  its 
general  form,  and  be  one-quarter  of  an  inch  larger  in  each  direction. 
The  ring  should  be  deep  enough  to  extend  one-quarter  of  an  inch 
above  the  cutting  edges  of  the  teeth.  The  ring  thus  prepared  is  now 
set  on  a  glass  slab  and  attached  thereto  by  passing  a  hot  spatula 
around  its  edge.  This  forms  a  cup-hke  matrix  into  which  the  invest- 
ment is  cast. 

The  investment  is  now  mixed  as  described  above  and  first  applied 
thoroughly  to  the  palatal  surface  of  the  plate,  allowing  it  to  flow  between 
and  over  all  exposed  portions  of  the  teeth.  The  matrix  is  filled  three- 
quarters  full  and  the  plate  inserted,  palatal  surface  downward,  and 
pressed  down  until  it  is  within  one-sixteenth  of  an  inch  of  the  glass 
slab.  The  excess  of  material  is  forced  up  and  around  the  teeth,  cover- 
ing the  incisal  and  occlusal  surfaces  to  a  depth  of  one-sixteenth  of  an 
inch  and  filling  in  the  lingual  side  of  the  vault. 

The  investment  should  be  fully  set  before  it  is  removed  from  the 
matrix.  After  it  is  thoroughly  dry  and  hard,  the  wax  may  be  detached 
from  the  teeth  by  subjecting  the  case  to  dry  heat  until  the  platinum  be- 
comes warm,  when  the  wax  may  be  readily  removed.     Hot  water  should 


646 


CONTINUO  US-G  UM  DKyTURES. 


never  be  used  as  it  destroys  the  integrity  of  the  investient  material, 
thereby  frequently  eausing  it  to  fracture  under  the  subsecjuent  applica- 
tion of  heat. 

All  surfaces  from  which  the  wax  has  been  removed  are  to  be  thoroughly 
cleansed  with  chloroform. 

SOLDERING. 

The  pins  of  the  teeth  are  bent  so  they  are  in  perfect  contact  with  the 
wire  and  plate.  Small  sfpiares  of  platinum  solder  are  placed  at  these 
points  of  contact  and  retained  in  position  by  a  coating  of  borax.  The 
borax  is  not  intended  as  a  flux,  as  the  noble  metals  do  not  oxidize  and 
a  flux  is  not  required,  but  it  keeps  the  solder  in  place. 

There  are  numerous  methods  of  heating  up  the  case  preparatory  to 
soldering.  Quite  a  satisfactory  one  which  the  author  has  frequently 
used  is  to  set  the  invested  case  in  a  bed  of  broken  pieces  of  burnt  fire- 
clav  over  a  Bunsen  burner.  This  fire-clay  is  prepared  by  incorporating 
with  it  starch  or  sawdust,  breaking  it  up  into  pieces  of  suitable  size,  and 


Fig.   577 

S^^ 

W^k 

(b'  *^ 

dBfeki-  ^ 

\ 

3K'*  i 

I 

^ 

m  t 

.1 

^^>^: 

r 

Full  upper  base-plate,  showing  wire  soldered  upon  top  of  ridge  and  teeth  soldered  on. 

firing  them.  The  combustible  constituents  burn  out,  leaving  the  pieces 
porous.  When  thus  prepared  the  mass  may  be  heated  thoroughly  in 
a  very  short  time,  and  it  also  possesses  the  advantage  of  cooling  slowly. 

With  the  aid  of  an  ordinary  gas  blowpipe  the  case  is  gradually  heated 
to  a  dull  orange  color  (2000°  F).  The  flame  from  the  oxy-hydrogen 
blowpipe  is  then  directed  against  the  parts  to  be  soldered  until  the  sol- 
der  flows. 

Each  pin  should  be  carefully  examined  to  see  that  it  is  securely  at- 
tached to  the  wire  or  plate.  When  we  are  assured  of  this  the  case  is 
allowed  to  cool  gradually;  this  is  conveniently  done  by  placing  a  cover 
over  the  receptacle  containing  it.  When  quite  cool  the  investment  is 
removed  and  the  denture  boiled  in  dilute  sulphuric  acid,  and  Wiished 
in  water  until  every  trace  of  foreign  substance  is  removed.  It  is  now 
readv  for  its  final  trial  in  the  mouth.     The  adhesion  and  articulation 


SOLDERING.  647 

are  noted;  any  slight  corrections  in  the  arrangement  of  the  teeth  may 
be  made  at  this  time.  After  it  is  removed  from  the  mouth  the  plate  is 
placed  on  the  cast,  and  all  surfaces  of  the  platinum  to  which  the  porce- 
lain is  to  be  applied  are  roughened  by  gentle  scratching  with  a  sharp 
excavator. 

The  plate  is  made  scrupulously  clean  by  washing  with  chloroform  or 
alcohol  and  is  ready  for  the  first  application  of  body.  The  utmost  de- 
gree of  cleanliness  must  be  observed  in  all  the  subsequent  manipula- 
tions. Any  dust  or  particles  of  foreign  matter  coming  in  contact  with 
the  porcelain  body  will  seriously  affect  the  beauty  and  integrity  of  the 
finished  product. 

The  Porcelain  Body  and  its  Manipulation. — The  degree  of  success  to 
be  achieved  now  depends  upon  the  skill  and  judgment  manifested  in 
dealing  with  the  purely  ceramic  features  of  the  case.  The  manipula- 
tion of  the  porcelain  paste  is  considered  in  three  stages;  upon  the  ap- 
plication and  carving  of  the  first  coat  of  body  largely  depends  the  final 
artistic  effect.  For  the  application  of  the  paste  and  its  aesthetic  carving 
the  set  of  instruments  illustrated  in  Fig.  578  will  be  found  very  useful. 

Fig.  678 


Instruments  for  carving  the  porcelain  paste. 

The  porcelain  body  is  prepared  on  a  clean  glass  slab.  It  is  mixed 
into  a  paste  with  distilled  w^ater  to  the  consistence  of  thick  cream. 
It  is  applied  first  to  the  lingual  concavity  of  the  palatal  portion  of  the 
plate,  betw^een  and  about  the  roots  of  the  teeth,  jarring  the  plate  at  in- 
tervals to  insure  compactness  of  the  body.  The  moisture  rising  to  the 
surface  is  to  be  absorbed  with  clean  blotting  paper  cut  into  strips  for 
the  purpose.  If  slight  pressure  is  exerted  with  the  blotting  paper  upon 
the  surface  of  the  body,  it  will  be  condensed  and  less  shrinkage  will  en- 
sue. When  this  portion  is  covered  uniformly  to  the  proper  thicknesS; 
which  is  that  of  No.  24  gauge,  the  rugae  and  other  features  found  in 
the  roof  of  the  mouth  are  modelled  in  the  body. 

On  the  labial  and  buccal  surfaces  the  paste  is  applied  in  the  same 
manner.  The  contours  of  these  regions  are  roughly  brought  out  in  the 
manipulation  of  the  body,  but  no  attempt  is  made  at  accurate  carving. 
No  instructions  may  be  given  as  to  the  correct  car^dng  of  these  features. 
This  must  be  learned  by  a  close  observation  of  nature  and  by  abundant 
practice.  The  crowns  of  the  teeth  are  kept  well  defined  and  thoroughly 
freed  of  any  adhering  porcelain  paste. 

To  prevent  the  teeth  from  mo\ang  and  the  plate  from  warping  by 
the  contraction  of  the  body  in  fusing,  it  is  necessary  to  take  into  account 
the  shrinkage  which  will  take  place  in  this  process.     Shrinkage  occurs 


(j48  nJMlSUOUS-GUM  J)Ju\TURh\S. 

hi  three  stages  of  the  baking :-first,  as  the  water  dries  out  of  the  mass 
and  the  sohd  particles  more  closely  approximate  each  other;  second, 
when  the  particles  begin  to  combine  b)  fusing;  third,  as  the  mass 
becomes  vitrified.  The  principal  cause  of  shrinkage  may  be  said  to 
be  the  agglomeration  of  the  particles  which  were  previously  mechan- 
ically separated  by  the  water  expelled  in  the  drying  out  process.  This 
is  followed  by  the  fusing  of  the  component  parts  of  the  body,  and  fur- 
ther contraction  is  due  to  this. 

When  the  mass  of  porcelain  is  attached  to  a  platinum  base,  it  will 
either  separate  at  its  weakest  place  or  the  plate  will  warp;  consequently, 
to  prevent  either  of  the  above  contingencies,  shrinkage  must  be  pro- 
vided for  by  dividing  it  into  small  masses  so  disposed  that  their  contrac- 
tion will  neither  disarrange  the  teeth  nor  warp  the  plate.  A  fine  ribbon 
saw  is  passed  between  each  tooth  dividing  the  body  entirely  to  the 
base.     The  cuts  are  continued  on  the  lingual  aspect  of  the  plate. 

It  is  noticed  in  firing  the  low  fusing  bodies,  that  the  contraction  is 
largely  vertical,  because  of  their  tendency  to  assume  a  gloV)ular  form 
when  fused.  The  high  fusing  bodies  stand  as  carved,  contracting  sym- 
metrically to  the  mass  when   uninfluenced  by  any  extraneous  factors. 

The  case  now  ready  for  the  first  baking,  is  placed  in  the  furnace 
resting  upon  the  palatal  portion  of  the  original  investment,  or  better, 
upon  a  support  of  iridio-platinum  wire  bent  into  a  "V"-shape  with  up- 
turned ends. 

FURNACES. 

The  great  length  of  time  necessary  to  heat  up  the  old  style  porcelain 
furnaces  was  a  strong  objection  to  this  kind  of  work;  consequently,  to 
meet  the  requirements  of  the  present  day  a  furnace  intended  for  con- 
tinuous-gum work  must  be  available,  which  can  be  used  with  the  ex- 
penditure of  less  time  than  formerly.  It  must  be  so  constructed  that 
there  is  no  possibility  of  a  contamination  of  the  porcelain  denture  by 
the  products  of  combustion. 

Wherever  it  is  possible  to  use  it  the  operator  will  make  no  mistake 
in  selecting  one  of  the  approved  electric  furnaces  which  the  manufactur- 
ers are  now  offering.  Among  the  many  advantages  possessed  by  this 
type  of  instrument,  may  })e  mentioned  the  facility  with  which  it  may  be 
handled,  and  the  small  space  which  it  occupies.  With  it  there  is  no 
danger  of  "gasing"  the  work.  Its  cleanliness,  the  complete  absence  of 
odor  and  noise,  and  its  beauty  of  finish  as  now  constructed,  recommend 
it  highly  in  the  furnishing  of  a  well  ec|uipped  laboratory.  If  lack  of  space 
in  the  laboratory  prevents,  it  may  even  find  a  place  in  the  operating 
room.  The  chief  advantages,  however,  of  the  electric  furnace  are  the 
ease  and  accuracy  with  which  the  requisite  heat  may  be  applied,  con- 
trolled, and  maintained.  The  construction  of  the  furnace  is  such  that 
the  case  may  be  heated  uniformly  and  evenly  throughout,  the  degree  of 
heat  is  under  perfect  control,  and  it  is  claimed  that  porcelain  fused  by 
this  method  possesses  unusual  clearness  and  density. 


furnaces:  640 

In  those  localities  where  the  electric  current  is  not  available,  the 
operator  may  find  his  demands  satisfactorily  met  by  the  use  of  some 
form  of  the  gasoline  furnace.  Very  excellent  results  may  be  obtained 
by  this  method  of  fusing  porcelain  and  the  country  practitioner  need 
not  hesitate  to  undertake  the  work  with  a  furnace  of  this  character.  The 
electric,  gas  and  gasoline  furnaces  are  described  in  the  Chapter  on  the 
Laboratory. 

A  thorough  acquaintance  with  the  management  of  the  furnace 
is  indispensable,  as  probably  the  most  prolific  source  of  failure  in 
continuous-gum  work  is  lack  of  knowledge  in  this  regard.  Each  indi- 
vidual furnace  should  be  accurately  tested  by  the  operator  and  its 
working  capabilities  carefully  observed.  The  temperatures  at  which  the 
different  porcelain  bodies  and  enamels  fuse  should  be  noted;  also  the 
effects  produced  upon  them  by  variations  above  and  below  their  fusing 
points.  Where  a  case  necessitates  several  bakings  with  the  same 
body  the  temperature  scale  must  be  marked  for  the  proper  limit  of 
fusing  for  each  baking.  Because  of  the  fact  that  the  formulae  of  porce- 
lain bodies  and  enamels  on  the  market  vary  in  composition,  fusibility 
and  other  physical  properties,  no  general  rule  can  be  given  for  the 
regulation  of  temperatures.  If  the  composition  of  all  the  bodies  was 
the  same  and  their  working  qualities  were  constant,  the  fact  would  still 
remain,  that  each  furnace  is  a  law  unto  itself.  This 
applies  not  only  to  furnaces  of  different  manufacturers  ^^^'-  ^"^^ 

but  to  those  of  the  same  make. 

Until  recently,  no  positive  test  for  the  correct  fusing 
point  was  known.  Fairly  good  results  may  be  obtain- 
ed by  placing  a  pellet  of  pure  gold  in  the  muffle  of  the 
furnace  near  the  plate,  and  after  this  melts  at  2016°  F,, 
by  maintaining  the  heat  for  a  definite  length  of  time. 

More  accurate  results  are  secured  by  using  the  pyro- 
meter (Fig.  579),  designed  by  the  author.  This  device  "  by  the  author. 
is  exceedingly  simple  in  construction.  A  small  cube  of 
soap-stone  is  excavated  to  resemble  an  hour  glass;  into  the  upper  ex- 
panded cavity  is  placed  a  small  spherical  mass  of  an  alloy  composed  of 
platinum  and  gold.  The  relative  proportion  of  the  two  metals  governs 
the  fusing  point  of  the  alloy ;  so  by  varying  the  proportions,  the  tempera- 
ture may  be  graduated  to  any  extent  within  the  limits  desired.  The  pro- 
per temperature  of  fusing  foi  a  given  body  is  matched  with  a  pellet  of 
alloy.  The  pyrometer  is  set  in  the  muffle,  and  when  the  temperature  at 
which  the  porcelain  fuses  has  been  reached,  the  little  metal  ball  melts 
and  runs  down  into  the  lower  chamber. 

Below  are  tabulated  the  results  of  experiments  conducted  by  the 
writer  with  the  pyrometer  to  determine  the  fusing  points  of  some  of  the 
more  prominent  porcelain  bodies  found  on  the  market. 


Allen's  body 

2340°  F, 

Close's  body 

2290° 

White's  inlay 

2260° 

Brewster's  foundation 

2220° 

Consolidated  continuous-gum 

2200° 

650  coyTiNUous-auM  benturks. 


Consolidated  inlay 

2140° 

Whiteley's 

21-10° 

Brewster's  enamel 

2090^ 

Ash  high  fusing 

20 10'^ 

Jenkins  prosthetic 

1830° 

Jenitins  inlay 

15800 

Gum  enamel  (Close  and 

Whiteley's  combined) 

2140° 

In  the  further  prosecution  of  these  experiments,  the  writer  is  led  to  the 
conckision  that  the  maximum  strength  obtainable  in  porcelain  is  devel- 
oped by  the  proper  regulation  of  the  heat.  If  underbaked  it  will  be 
brittle,  flaked  and  incapable  of  withstanding  the  stress  of  mastication; 
while  overbaking  causes  porosity  and  diminution  in  power  to  resist 
crushing  stress. 

First  Baking. — The  piece  is  placed  in  the  muffle  of  the  electric  fur- 
nace. It  is  desired  to  heat  it  up  slowly  at  first,  so  that  it  may  dry  out, 
and  so  that  it  will  not  flake  by  the  sudden  formation  of  steam  in  the  body 
from  the  water  used  in  mixing  it.  The  heat  is  turned  on  and  gradually 
raised,  placing  the  lever  of  the  rheostat  on  the  first  button.  It  is  allowed 
to  remain  on  the  first  button  for  five  minutes  and  then  turned  to  the 
next  button;  on  this  and  each  of  the  following  buttons  it  remains  two 
or  three  minutes,  until  the  last  one  is  reached,  w  here  it  rests. 

During  this  time  the  case  is  watched  carefully  to  determine  the  proper 
degree  of  baking.  Less  heat  is  required  for  this  than  for  subsequent 
firings.  The  baking-  is  carried  to  what  is  known  as  the  granular 
stage,  at  which  point  all  shrinkage  has  taken  place.  The  surface  is 
not  cjuite  glazed,  but  presents  rather  a  frosty  appearance. 

When  the  process  of  fusion  has  reached  the  desired  stage  as  indi- 
cated by  the  pyrometerj  the  rheostat  is  thrown  back  and  the  current 
turned  off  and  the  case  allowed  to  remain  in  the  muffle  until  cooled. 
It  is  then  placed  upon  the  die  and  the  rim  turned  with  flat-nose  pliers 
and  riveting  hammer,  holding  the  plate  firmly  in  place.  The  rim  is 
turned  to  the  desired  angle,  which  depends  upon  the  thickness  of  the 
gum,  the  purpose  being  to  make  the  external  surface  of  the  rim  and  that 
of  the  porcelain  of  the  gum  continuous  in  the  finished  piece.  The 
case  then  presents  the  appearance  illustrated  in  Figs.   580  and  581. 

The  plate  is  now  ready  for  the  second  application  of  porcelain. 
The  paste  is  mixed  and  applied  as  in  the  first  instance,  filling  in  the  fis- 
sures and  restoring  more  fully  the  contours.  When  this  is  done,  all 
traces  of  the  paste  are  removed  from  the  surfaces  of  the  crowns  of  the 
teeth  and  platinum  base  which  is  not  to  be  covered  with  porcelain. 
This  may  be  done  with  a  camel's  hair  brush,  the  bristles  of  which  have 
been  cut  oft'  close  to  make  them  stiff.  The  plate  is  now  placed  in  the 
muffle  as  before  and  subjected  to  the  second  firing.  The  temperature 
for  this  operation  is  carried  a  few  degrees  higher  than  in  the  first  baking 
in  order  to  produce  more  complete  fusion  of  the  porcelain  body.  The 
porcelain  body  is  brought  just  to  the  verge  of  a  glaze:  its  surface  should 
show  a  sparkling  granulated  appearance.  Carrying  the  heat  beyond 
the  stage  necessary  to  produce  this  effect  lessens  the  strength  of  the 


APPLYING    THE  GUM  ENAMEL. 


651 


porcelain,  aiul  makes  it  impossible  to  obtain  the  translucent  appearance 
of  the  gum  when  the  gum  enamel  is  applied.     (Fig.  582.) 

After  beino-  allowed  to  cool  as  before,  the  plate  is  tried  in  the  mouth 
to  note  if  any  alterations  in  its  form  have  taken  place.  The  extent  of 
the  buccal  and  labial  contours  of  the  plate  is  also  noted.  If  too  full  at 
any  place  they  may  be  reduced  by  grinding;  if  lacking  at  others,  more 
porcelain  may  be  added,  and  the  piece  rebaked. 

Fig.  580 


Labial  and  buccal  view  of  denture  after  first  baKing. 

Applying  the  Gum  Enamel  . — The  gum  enamel  is  now  prepared  by 
mixing  it  with  distilled  water  and  it  is  applied  in  the  same  manner  as  the 
body.  The  denture  should  be  wet  to  facilitate  the  placing  of  the  enamel. 
This  layer  should  be  thin  and  so  applied  as  to  preserve  the  distinctness  of 
the  gum  outlines.  By  varying  its  thickness  those  differences  in  shade 
observed  in  the  natural  gum  over  the  roots  of  the  teeth  may  be  secured 


Fig. 

5S1 

^^m  ■€  -^^^K 

H 

^t\ 

Cm 

■ 

^1 

Ftg-   582 


Lingual  view   of  full  upper  denture  after 
first  baking. 


Lingual  view  of  partial  upper  denture  after 
second  baking. 


as  the  yellowish  white  of  the  body  is  allowed  to  show  through  more  or 
less  clearly  at  these  points.  The  outlines  of  the  necks  of  the  teeth,  and 
rugae  are  clearly  defined.  All  superfluous  portions  of  the  paste  are  care- 
fully removed,  using  small  camel's  hair  brushes  and  instruments  de- 
signed for  the  purpose.  The  piece  is  again  subjected  to  the  heat  of  the 
furnace. 


652 


CONTJNUO US-G I'M  DESTURKS. 


The  exact  degree  of  heat  necessary  to  develoj)  the  full  beauty  and 
strength  of  the  case  can  only  be  deterniin(Hl  by  ex])erience.  ^Vhen  the 
heat  approaches  the  fusing  point,  it  is  well  to  turn  off  the  current  and 
make  an  inspection.  When  finished,  it  should  present  a  smooth,  glossy 
appearance.  If  the  heat  is  carried  a  few  degrees  too  far,  the  color 
begins  to  fade  and  its  brilliancy  is  lost.  Frequently  little  pieces  become 
detached  and  minute  cracks  present  themselves.  These  defects  may 
be  remedied  by  applying  more  enamel,  and  repeating  the  baking.  The 
natural  gum  effect  cannot  always  be  secured  with  the  enamels  as  found 
on  the  market.  A  combination  of  several  of  them  often  produces  the 
shades  desired.  The  writer  obtains  desirable  results  in  many  cases 
by  combining  the  Close  and  Whiteley  gum  enamels  and  adding  asmall 
quantity  of  White's  inlay  body.  Doubtless  other  combinations  pro- 
(iuce  equally  good  results.  With  the  exercise  of  patience  the  operator 
can  obtain  almost  anv  shade  desired. 


Fig.  oSo 


Ftg.  584 


Lingual  view  of  upper  denture  after  liaking 
of  gum  enamel. 


Lingual  \iew  of  upi^er  denture  after  baking 
of  gum  enamel. 


The  finishing  process  consists  simply  in  smoothing  and  polishing 
the  metallic  surfaces  and  washing  the  plate.  The  metal  portions 
must  have  any  marks  due  to  files  or  pliers  removed,  and  the  polishing 
i^  done  on  the  lathe  in  the  same  manner  as  for  any  other  metal  plate. 

Mineral  Paints. — As  previously  mentioned,  there  are  often  condi- 
tions of  the  natural  organs  associated  with  decay  and  discoloration 
from  other  causes,  which  may  be  imitated  in  the  ])orcelain  teeth  by  the 
judicious  application  of  mineral  paini's.  The  method  of  applying  and 
fusing  these  paints  may  be  readily  learned,  and  a  little  study  in  the 
mixing  and  blending  of  colors  will  enable  the  operator  to  produce  very 
correct  imitations  of  these  defects  in  natural  teeth.      (See  Chapter  XII.) 

These  stains  are  applied  on  or  around  the  cervical  margins,  the  cut- 
ting edges,  occlusal  surfaces,  or  any  other  portion  of  the  tooth,  imitating 
those  discolorations  seen  in  the  recession  of  the  gums,  mechanical  ab- 
rasion, devitalized  or  decayed  teeth.     The  effect  is  still  more  pleasing 


FUJJ.   LOWER   DENTURE.  653 

If  previous  to  staining,  the  cusps  or  edges  of  the  tectli  are  ground  off  to 
imitate  the  wear  incident  to  age.  Pitting  or  other  defects  of  structure 
which  obtained  in  the  natural  teeth,  may  be  well  imitated  by  this  pro- 
cedure. There  is  practically  no  limit  to  the  possibilities  offered  by  this 
process  in  the  hands  of  a  skilled  operator. 

FULL  LOWER  DENTURE. 

The  general  considerations  set  forth  under  the  discussion  of  the  full 
upper  continuous-gum  denture,  apply  equally  to  other  forms  of  den- 
tures embraced  under  this  title.  Hence  in  discussing  the  full  lower  or 
the  partial  upper  and  lower  dentures,  it  will  only  be  necessary  to  men- 

FiG.  585 


Buccal  and  labial  view  of  denture  after  baking  of  gum  enamel    showing  imitation  of  recession  of 
gums,  and  staining  of  necks  of  the  teeth. 

tion  those  departures  from  the  general  line  of    procedure  which  are 
made  necessary  by  the  requirements  of  the  particular  case. 

The  first  step  in  the  construction  of  the  full  lower  case  is  that  of  form- 
ing the  pattern.  Heavy  tin  foil  is  accurately  adapted  to  the  die  and 
trimmed  shghtly  larger  than  the  plate  outline  to  provide  for  any  pos- 

FiG.  586 


n 

Buccal  and    labial  view    of  denture    after    baking  of  gum  enamel  showing  omission  of  one  tooth 

and  irregular  alignment. 

sible  displacement  of  the  plate  in  swaging.  Great  care  must  be  ob- 
served in  preparing  patterns  for  lower  and  partial  cases  to  prevent 
change  of  form  when  the  tin  foil  is  flattened  out,  for  should  this  occur, 
a  plate  cut  to  such  an  inaccurate  pattern  would  be  useless.  Because  of 
the  inherent  weakness  in  the  shape  of  a  lower  plate,  heavier  gauges  a,re 
used  than  for  upper  cases,  and  furthermore,  these  are  specially  reinforced. 


654 


CONTIN  UO  US-G  UM  DEyTURES. 


The  quality  of  li<^htness  is  not  so  mucli  a  desideratum  as  in  the  upper 
phite,  and  .strength  may  he  gained  in  this  manner  without  atteeting  the 
sueces.s  of  the  denture.  Tlie  pattern  is  re[)ro(hieed  in  No.  2S  to 
No.  30  gauge,  phitinum  phite,  and  this  is  reinforeed  around  the  anterior 
Hngual  curve  with  a  piece  of  iridio-platinum  plate  No.  26  gauge.  The 
supj)lementary  piece  should  extend  from  the  rim  on  the  lingual  surface, 
U])  and  well  over  the  ridge  as  in  Fig.  587. 

The  rim  may  be  turned  as  for  an  upper  plate  if  it  is  desired,  but  a 
platinum  wire  No.  18  gauge,  soldered  along  the  borders  of  the  plate  is  to 
be  preferred.  This  will  not  only  provide  additional  strength,  but  it 
permits  the  trimming  of  the  plate  edges  which  is  so  often  necessary 

Fir..   587 


Reinforcement  of  full  and  partial  lower  plates. 


with  lower  dentures.  An  iridio-platinum  wire  No.  14  to  10  gauge,  is  to 
be  adjusted  on  the  ridge  of  the  plate  under  the  pins  of  the  teeth, 
as  in  the  upper  plate.  This  serves  for  the  attachment  of  the  pins. 
The  subsequent  procedures  are  the  same  as  those  outlined  for  a  full 
upper  case. 


PARTIAL  DENTURES. 

Continuous-gum  is  employed  to  best  advantage  for  partial  restora- 
tions in  those  ca.ses  in  which  the  teeth  to  be  replaced  are  in  an  unbroken 
column.  More  patience  and  skill  are  required  in  the  construction  of 
partial  dentures  than  in  either  a  full  upper  or  lower.  Each  individual 
case  presents  features  peculiar  to  itself,  and  each  will  suggest  the  proper 
procedure.  The  chief  difficulties  encountered  are  in  preventing  the 
plate  from  folding  or  splitting  during  the  swaging.  Frequent  anneal- 
ing, the  skillful  u.se  of  the  pliers  and  mallet,  and  the  cutting  away  of  the 
surplus  metal  at  difficult  points  about  the  natural  teeth,  will  aid  in 
avoiding  the.se   dangers. 

Partial  Upper  Dentures. — When  a  partial  upper  case  presents,  the 
first  thing  to  be  determined  is  the  mode  of  retention.  There  are  two 
general  methods  by  which  the  stability  of  the  plate  in  the  mouth  may  be 
secured.     In  the  one  case,  the  retention  is  obtained  l)v  the  combined 


PARTIAL  DKNTURKS. 


655 


forces  of  atmospheric  pressure  and  adhesion,  the  plate  covering  the  en- 
lire  surface  of  the  hanl  pahitc.  In  the  other  case  the  retention  depends 
upon  attachment  to  the  natural  teeth  remaining  in  the  arch,  the  plate 
being  in  the  form  of  a  horseshoe,  and  covering  only  the  alveolar  ridge. 

To  illustrate  the  application  of  the  first  method,  we  may  take  a  form 
of  denture  carrying  the  posterior  teeth.  Obviously,  retention  by  clasps 
in  this  case  would  be  unsatisfactory,  although  it  is  possible  even  here  to 
obtain  fixation  in  or  to  the  natural  organs  by  special  means.  Two  pat- 
terns are  prepared:  that  for  the  primary  plate  extending  over  all  sur- 
faces intended  to  be  covered;  viz — the  vault  of  the  mouth,  alveolar 
ridges  and  buccal  surfaces.  This  is  reproduced  in  No.  34,  platinum 
plate.  The  second  pattern  is  reproduced  in  No.  30,  iridio-platinum 
plate.     It  conforms  to  the  shape  of  the  first  except  that  it  does  not  ex- 


tend over  the  ridges. 


Fig.  588 


Full  upper  denture  with  lingual  surface  of  teeth  carved  in  porcelain;  denture  carrying  large 

contours.     (Wilson.) 

Each  lamina  is  swaged  separately  and  then  the  two  are  swaged  to- 
gether. They  are  then  united  with  platinum  solder,  the  lateral  margin 
of  the  supplementary  piece  being  left  free  to  form  the  lingual  boundary 
of  the  porcelain.  In  this  case  the  palatine  surface  is  not  covered  with 
(he  body  and  no  rim  across  the  posterior  border  is  required.  The  buc- 
cal rim  may  be  formed  by  turning  or  wiring. 

The  patterns  for  the  denture  to  be  retained  by  the  second  method  are 
adapted  to  the  cast,  and  conform  to  the  horseshoe  shape,  leaving  the 
height  of  the  vault  free.  The  denture  is  preferably  constructed  of  two 
laminae,  the  primary  of  No.  30  gauge  platinum,  the  second  of  No.  26  to 
No.  28  gauge,  iridio-platinum  plate.  They  may  be  cut  to  the  same  pat- 
fern,  though  the  borders  of  the  first  should  be  allowed  to  project  shghtly 
to  provide  support  for  the  solder.  The  rim  and  lingual  boundary  of 
the  porcelain  is  formed  by  attaching  No.  18  platinum  wire.  This  style 
of  denture  may  be  used  to  replace  the  anterior  teeth  with  some  of  the 
bicuspids  or  molars  remaining  to  afford  attachment  for  the  clasps. 
These  latter  are  adjusted  as  for  other  swaged  plates,  but  iridio-platinum 


656 


coy  TIN  ijo  us-a  um  i>ks  tur  ks. 


must  DC  used  instead  of  tlie  elasp  metal,  as  the  latfcn-will  not  stand  the 
high  temperatures  of  poreehiin  hakiug. 

Coml)ination  ehisps  of  phitinum  and  elasp  metal  may  be  made  and 
attached  in  the  following  manner:  the  clasp  metal  is  cut  and  adapted 
to  conform  properly  to  the  tooth;    around  this  is  adapted  thin  iridio- 


Fir..   o8<l 


Ooclusal  view  of  completed  full  lower  dentures. 

platinum.  The  iridio-platinum  clasp  is  waxed  to  the  plate,  removed, 
invested  and  soldered.  It  also  serves  as  a  matrix  against  which  to 
build  the  Ixxly.  The  ceramic  part  of  the  denture  is  then  finished  and 
the  gold  clasp  placed  in  position  in  the  attached  clasp,  properly  in- 
vested and  soldered  with  IS-carat  gold  solder.     The  objection  to  this 

Fig.  590 


Lingual  view  of  completed  upper  denture. 


combination  lies  in  the  fact  that  in  case  the  denture  requires  repairing, 
the  use  of  low  fusing  body  is  necessitated. 

Partial  Lower  Dentures. — An  ordinary  form  of  partial  restoration  to 
which  continuous-gum  is  applicable  is  that  replacing  the  inferior  bicus- 
pids and  molars.      For  these  cases  the  pattern  is  reproduced  in  plati- 


TUBE  TEETH  WITH  CONTINUOUS-GUM.  657 

num  plate,  No.  30.  A  common  source  of  annoyance  in  swaging  plates 
for  such  a  case  is  the  teuchnicy  of  the  anterior  part  of  the  plate  to  dis- 
placement downward  on  the  die.  This  may  be  pi'evented  by  allowing 
the  sheet  metal  to  extend  over  that  part  of  the  die  representing  the  teeth 
and  by  bending  it  over  their  occlusal  ends.  A  reinforcing  piece  of  No. 
24  iridio-platinum  plate  is  applied  to  that  portion  of  the  lingual  sur- 
face of  the  plate  lying  behind  the  natural  teeth.  This  should  extend 
well  beyond  the  remaining  teeth  on  each  side  and  from  the  lower  to  the 
upper  borders  of  the  plate.  The  break  in  the  continuity  of  the  plate  at 
the  site  of  the  natural  organs  makes  it  imperative  that  additional 
strength  be  provided  to  overcome  the  natural  weakness  at  this  point. 

The  rim  is  formed  by  soldering  platinum  wire  No.  18  to  the  free  mar- 
gins of  the  plate.  The  other  boundaries  which  limit  the  porcelain 
should  likewise  be  covered  with  the  wire.  It  will  be  observed  in  the 
illustration  (Fig.  587)  that  the  porcelain  is  not  to  be  carried  across  the 
anterior  lingual  surface  but  is  limited  by  the  wire.  If  the  curve  of  the 
alveolar  ridge  is  marked  the  plate  may  be  braced  as  illustrated  in  Fig. 
587. 

TUBE  TEETH  WITH  CONTINUOUS-GUM. 

M.  B.  Platschick  of  Paris,  has  a  very  ingenious  method  for  the  use  of 
tube  teeth  in  the  construction  of  continuous-gum  dentures,  by  means  of 
which  he  obviates  the  necessity  of  primarily  attaching  the  teeth  to  the 
plate  with  solder. 

A  platinum  plate  of  full  size  is  swaged  after  the  ordinary  methods; 
then  another  narrow  plate  is  swaged  to  cover  only  the  ridge  or  places 
where  the  pins  are  to  be  attached  and  the  two  are  soldered  together.  The 
plate  is  then  tried  in  the  mouth  and  adjusted  perfectly,  any  impinge- 
ment upon  movable  tissues  being  relieved  by  trimming. 

The  rim  is  formed  by  soldering  to  the  buccal  and  labial  margins  of 
the  plate  a  platinum  v/ire  of  special  form  obtained  by  means  of  a  draw 
plate  designed  to  produce  it.  In  addition  to  furnishing  a  rim,  this  also 
reinforces  the  piece,  and  the  form  of  the  wire  is  such  that  a  recess  is  left 
under  its  margin  for  the  attachment  of  the  porcelain  body.  It  also 
permits  the  making  of  changes  by  trimming  which  maybe  subsequently 
necessary  despite  the  most  careful  fitting  of  the  plate  when  it  is  tried  in 
the  mouth. 

The  tube  teeth  are  now  ground  and  roughly  adjusted  to  the  plate 
A  fine  adjustment  would  be  unnecessary,  as  the  little  spaces  existing 
between  the  teeth  and  plate  are  easily  filled  in  with  the  porcelain  body. 
When  the  teeth  are  adjusted  and  the  articulation  is  satisfactory,  the 
teeth  are  secured  to  the  plate  with  wax  to  maintain  them  in  position. 
A'  plaster  wall  is  formed  over  their  external  surfaces,  the  wax  is  removed 
and  with  a  sharp  pointed  instrument  passed  through  each  tube  the 
positions  of  the  pins  are  marked  upon  the  plate.  The  pins,  of  iridio- 
platinum  wire  fitting  the  tubes,  are  adjusted  and  soldered  in  place  as 
indicated  by  the  marks  on  the  plate.      The  piece  is  now  pickled  and 

42 


658  CONTINUOUS-GUM  DENTURES. 

washed  tlioroughly,  after  which  the  appHcation  of  the  porcelain  is  be- 
gun. A  httle  porcelain  paste  is  applied  around  each  of  the  pins  and 
the  teeth  are  then  forced  over  them  into  place.  More  paste  is  then 
added  about  the  necks  of  the  teeth,  and  the  opening  on  the  occlusal 
surface  is  closed  in  like  manner.  The  teeth  are  now  fixed  in  their  re- 
spective positions  by  baking,  usually  two  firings  being  necessary  for  this 
purpose.  After  the  teeth  are  thus  fixed,  the  various  applications  of 
l>ody  and  enamel  are  made  as  previously  described  in  the  usual  pro- 
cedure. 

REPAIRING  CONTINUOUS-GUM  DENTURES. 

An  objection  formerly  urged  against  the  employment  of  continuous- 
gum  dentures  was  the  difficulty  of  repairing  them  in  case  of  fracture. 
The  validity  of  this  objection  could  not  be  questioned  when  the  old 
methods  were  in  vogue,  but  now  with  a  more  precise  knowledge  of  the 
materials  at  our  disposal,  and  with  the  valuable  acquisition  to  our  arm- 
amentarium of  the  electric  furnace,  we  are  enabled  to  undertake  oper- 
tions  for  the  repair  of  these  cases  with  the  assurance  of  complete 
success. 

When  a  case  is  presented  for  repair,  before  any  other  steps  are  taken, 
all  foreign  or  extraneous  material  must  be  completely  removed,  not  only 
from  the  free  surfaces  of  the  piece,  but  from  the  cracks  and  fissures  as 
well.  Any  such  material  allowed  to  remain  will  exercise  a  deleterious 
influence  upon  the  porcelain.  The  plate  should  first  be  scrubbed  in 
water  containing  a  little  ammonia.  To  ensure  effectually  the  further 
removal  of  the  accumulations,  the  plate  is  encased  in  an  investment  of 
asbestos  and  plaster,  placed  over  a  gas  stove,  and  gradually  heated  to 
redness.  During  this  process  the  foreign  matter  is  carbonized.  After 
cooling  slowly  the  plate  is  removed  from  the  investment,  washed  with 
soap  and  water,  and  further  cleansed  with  alcohol.  It  is  then  placed 
in  the  furnace  and  again  heated  to  redness. 

A  detached  fragment  of  a  tooth,  provided  the  line  of  fracture  be  dis- 
tinct, may  be  readily  replaced  by  the  aid  of  liquid  silex.  The  silex  is 
applied  to  the  broken  surfaces,  the  fragment  pressed  to  place,  and  the 
case  heated  in  the  furnace  to  an  orange-red  color.  This  gives  a  ready 
and  quick  method  for  this  kind  of  repair  wdiich  may  be  particularly 
useful  in  emergencies. 

No  attempt  should  be  made  to  replace  a  broken  tooth  or  teeth  until 
the  remaining  portions  are  ground  away.  On  the  lingual  surface  the 
porcelain  is  removed  until  the  platinum  base  or  wire  is  exposed.  The 
grinding  on  the  buccal  or  labial  surface  should  be  sufficient  to  permit 
the  proper  replacement  of  the  lost  tooth.  Teeth  are  selected  of  a  mold 
and  color  to  correspond  with  those  remaining  on  the  denture.  They 
are  ground  to  fit  the  spaces  prepared  for  them,  and  at  the  same  time  are 
given  a  correct  articulation.  They  are  waxed  in  position  and,  if  the 
length  of  the  column  of  teeth  to  be  replaced  demands  it,  they  are  given  a 
coating  of  shellac  varnish  and  the  piece  invested  to  hold  them  in  position. 


COMBINATIONS  OF  CONTINUOUS-GUM.  659 

This  wax  is  removed,  and  the  pins  are  attached  to  the  plate  as  pre- 
viously described,  this  time  however,  using  pure  gold  as  the  connecting 
medium  and  the  furnace  as  the  means  to  fuse  it.  The  unequal  heating 
involved  in  soldering  with  the  blowpipe  would  endanger  the  integrity 
of  the  porcelain.  The  case  is  allowed  to  cool,  removed  from  the  in- 
vestment and  cleansed.  The  body  is  applied  and  baked  to  the  granular 
stage  after  which  the  enameling  is  done  as  before. 

It  is  feasible  to  replace  one  or  two  teeth  without  attaching  the  pins  to 
the  plate  with  solder,  the  porcelain  material  alone  maintaining  them  in 
position.  In  simple  repairs  of  this  kind  it  is  only  necessary  to  grind 
away  enough  porcelain  to  permit  the  tooth  to  be  set  in  place. 

The  teeth  may  also  be  retained  in  proper  position  by  adapting  a 
platinum  wire  No.  30  around  the  plate  to  rest  upon  the  labial  and  buccal 
surfaces  of  the  teeth.  The  ends  of  the  wire  are  engaged  between  or 
around  the  posterior  teeth  remaining  on  the  plate. 

If  there  is  a  break  in  the  continuity  of  the  platinum  base  and  it  is 
not  extensive,  it  may  be  repaired  by  grinding  away  the  porcelain  im- 
mediately about  it,  adapting  a  thin  piece  of  platinum  plate  to  the 
break,  and  soldering  it  with  pure  gold  in  the  furnace.  The  porce- 
lain body  and  enamel  are  then  applied  as  already  described. 

Cases  sometimes  present  which  after  years  of  service  cease  to  be  use- 
ful because  of  the  changes  in  the  mouth  incident  to  resorption  of  the 
process.  In  such  a  case  it  will  be  necessary  to  take  a  new  impression, 
obtain  dies  and  counter-dies  and  reswage  the  plate  after  removing  the 
teeth  and  porcelain.  This  may  be  done  by  subjecting  the  denture  to  a 
red  heat  under  the  blowpipe  or  in  the  furnace  and  then  plunging  it  into 
cold  water.  The  porcelain  will  fracture  and  may  be  easily  detached. 
All  the  porcelain  portions  of  the  denture  may  be  effectually  removed 
by  immersing  the  plate  in  hydrofluoric  acid  for  a  few  hours.  After 
reswaging  the  process  is  the  same  as  for  constructing  the  original  plate. 

COMBINATIONS  OF  CONTINUOUS-GUM  AND  VULCANITE. 

The  ingenuity  of  the  operator  may  find  a  fruitful  field  of  employment 
in  the  various  combinations  of  continuous-gum  with  vulcanite.  The 
lightness,  cheapness,  and  accuracy  of  adaptation  of  vulcanized  rubber 
may  at  times  be  joined  advantageously  with  the  aesthetic  qualities  of 
porcelain. 

Cases  presenting  extremely  long  bites  in  which  the  increased  weight 
of  the  continuous-gum  might  prove  objectionable,  may  with  advantage 
be  restored  by  such  a  combination.  A  cast  of  the  jaw  is  obtained, 
covered  with  a  base-plate  of  gutta-percha,  and  from  the  model  so  pre- 
pared, dies  and  counter-dies  are  made.  A  platinum  plate  No.  34,  is 
swaged  to  cover  the  alveolar  ridge,  making  no  provision  for  the 
rim.  The  plate  is  perforated  at  various  points,  and  through  these 
perforations  after  the  porcelain  body  has  been  applied,  but  before  bak- 
ing, retaining  pits  are  made  in  which  to  engage  the  vulcanite. 


(560  CONTINUOUS-GUM  DENTURES. 

The  plate  is  warmed  and  set  over  the  gutta-percha;  the  bite  taken 
and  the  articulation  of  the  teeth  secured  in  the  usual  way.  It  is  then 
separated  from  +he  gutta-percha,  invested,  and  the  teeth  soldered  to  the 
plate  or  stays.  The  body  and  enamel  are  applied  and  baked.  When 
this  part  of  the  denture  is  complete,  it  is  set  over  a  wax  base-plate,  the  ' 
articulation  adjusted,  and  the  waxing  process  completed.  The  case 
is  then  flashed  and  the  succeeding  steps  are  analogous  to  those  described 
in  the  Chapter  on  Vulcanite. 

Continuous-gum  sections  or  full  pieces  may  readily  be  constructed 
and  mounted  in  the  vulcanite  without  the  platinum  base.  Upon  a  base 
plate  of  wax,  continuous-gum  teeth  are  arranged  and  properly  articu- 
lated. The  hihial  and  buccal  contours  are  restored  in  wax;  a  coating 
of  shellac  is  applied  to  the  teeth  and  the  Case  is  removed  and  invested 
with  the  teeth  downward  in  a  horse-shoe  shaped  bed  of  investment 
material,  half  an  inch  thick,  placed  on  a  glass  slab.  The  investment  is 
built  about  the  wax  gum  covering  it  to  a  depth  of  half  an  inch  and  ex- 
tending well  over  its  edge.  The  wax  is  thoroughly  removed  after  the 
investment  becomes  hard.  An  iridio-platinum  wire.  No.  18,  is  adapted 
against  the  necks  of  the  teeth  under  the  pins  bending  the  latter  securely 
around  the  wire  to  maintain  the  teeth  in  place.  That  part  of  the  in- 
vestment previously  covered  l)y  the  wax  is  now  oiled,  and  the  porcelain 
paste  packed  in,  applying  it  between  and  in  front  of  the  roots  flush  with 
the  lingual  surface  of  the  teeth  to  take  the  place  of  the  wax.  The  case 
enclosed  in  the  investment  is  now  introduced  into  the  muffle  with  small 
pieces  of  pure  gold  applied  to  the  junction  of  each  pin.  The  gold  sol- 
der unites  the  pins  and  wire  and  at  the  same  time  the  porcelain  body  is 
baked. 

When  cool  the  case  is  removed  from  the  investment  and  cleansed; 
given  its  enamel  baking,  and  then  set  on  the  cast,  waxed  in  proper  posi- 
tion and  the  plate  is  finished  in  vulcanite. 


CHAPTER    XV  I. 

ARTIFICIAL  CROWNS. 
By  H.  H.  Burchard,  M.D.,  D.D.S.,  and  F.  A.  Peeso,  D.D.S. 

When  the  crowns  of  teeth  have  suffered  such  extensive  loss  of  sub- 
stance that  restoration  by  means  of  filhng  material  is  inadvisable,  the 
restoration  is  an  operation  of  prosthetic  dentistry. 

The  term  "artificial  crown,"  as  technically  appHed,  includes  only 
such  devices  as  are  made  in  the  dental  laboratory  and  subsequently  set 
as  a  single  piece  upon  a  prepared  root  or  remnant  of  tooth.  The  pieces 
knctwn  as  "partial  crowns"  are  also  included  in  this  category. 

The  first  example  of  crown  substitution,  mounted  according  to  the 
principles  governing  contemporary  crown  operations,  was  the  setting  of 
a  crown,  of  a  natural  tooth  upon  a  prepared  root,  the  support  being 
afforded  by  a  post  extending  from  the  enlarged  pulp-chamber  of  such 
a  crown  into  the  enlarged  canal  of  the  root. 

Fig.  591 


Porcelain  crown  with  wood  post. 

The  mechanical  principle  involved  in  this  mode  of  support  has  had 
constant  application.  The  next  variety  of  crown  employed  was  that  of 
porcelain,  the  post  support  being,  as  in  the  preceding  form,  a  hickory 
post  (Fig.  591.)  Subsequently  metallic  posts  were  substituted  for  those 
of  wood,  and  this  variety  is  the  typal  form  of  one  of  the  two  great  classes 
of  crowns  in  present  use. 

Metallic  crowns  resembling  those  of  the  present  day  were  employed 
early  in  the  present  century. 

CLASSES  OF  CROWNS. 

All  of  the  varieties  of  artificial  crowns  may  be  divided  into  two  great 
classes,  according  to  their  means  and  modes  of  support.  The  first 
class  includes  all  of  those  crowns  which  depend  for  fixation  upon  a  post 
anchored  in  an  enlarged  pulp-canal.  (Fig.  592.)  The  second  class  in- 
cludes those  which  have  their  retention  secured  by  means  of  a  con- 
tinuous band  encircling  the  neck  of  the  root.     (Fig.  593.) 

661 


662  ARTIFICFAL   CROWNS. 

Class  1  is  subdivided  into  two  orders;  first,  those  in  which  the  post 
is  an  integral  part  of  the  artificial  crown,  being  baked  in  it  or  soldered 
to  it  (Fig.  592,  A  and  B) ;  second,  those  in  which  the  post  is  firmly  an- 
chored in  the  pulp-canal,  as  a  primary  measure,  and  upon  this  support 
the  crown  itself  is  fixed  as  a  second  operation.     (Figs.  592  (\  595,  596.) 

A  sub-order  includes  the  collar  and  post  crown  (Fig.  592  D),  the  band 


Fig.  593 


Class  1,  Order  1, 


encircling  the  root  acting  as  a  subsidiary  support  to  the  root,  protecting 
it  against  fracture,  the  post  being  the  retentive  de\dce  proper. 

All  of  the  artificial  crowns  in  present  u.se  will  be  found  to  be  a  variety 
or  some  modification  of  one  of  these  classes. 


Fig.    595 


Fig.  596 


Class  1,  Order  2. 


Each  variety  is  designed  and  fitted  to  meet  definite  indications,  and 
the  application  and  choice  of  variety  are  determined  by  the  anatomi- 
cal, physiological,  and  pathological  condition  of  the  root  to  be  crowned 
and,  it  may  be,  of  the  surrounding  parts. 


ANATOMICAL  RELATIONS. 

The  first  consideration  is  the  position  of  the  root  to  be  crowned;  and 
the  second,  its  form.  Its  position  includes  the  class  of  tooth,  whether  it 
be  an  incisor,  canine,  bicuspid,  or  molar;  next,  its  relative  position  to  its 
neighbors  and  to  its  antagonists,  and  what  will  be  the  relations  of  the 
artificial  crown  in  the.se  particulars. 

Each  cla.ss  of  tooth  has  a  definite  office  to  perform,  and  there  is  in- 
volved in  the  performance  of  its  function  an  amount  and  variety  of 
stress  governed  by  the  position  of  the  tooth — i.  e.  the  class  to  which  it 


THE  FORMS  OF  THE  TEETH.  663 

belongs.  This  demands  in  the  supporting  structures  of  the  crown  and 
root  sufficient  resistance  to  secure  tlie  integrity  of  tlie  crown  and  roct  in 
tlie  performance  of  their  normal  functions. 

Incisors  by  their  positions  and  forms  are  designed  to  receive  and  re- 
sist stress  in  one  direction,  that  tending  to  force  them  outward. 

Canines  in  their  normal  relations  receive  stress  in  two  directions: 
two  forces  act  at  an  angle  upon  the  axis  of  the  tooth,  and  the  resultant 
of  these  forces  is  a  line  outward. 

Bicuspids  are  subjected  to  three  stresses — vertical,  outward,  and  in- 
ward; the  relative  amounts  of  stress  are  in  the  order  given.  The 
amount  of  the  outward  and  inward  stress  is  governed  primarily  by  the 
lengths  of  the  buccal  and  palatal  or  lingual  cusps ;  the  vertical  stress,  by 
the  area  of  the  occlusal   surface. 

Upon  molars  the  vertical  stress  is  greatest,  and  in  the  direct  ratio  of 
the  extent  of  masticating  surfaces;  the  lateral  stress  is  governed  by  the 
lengths  of  the  cusps. 

Artificial  crowns  should  be  made  of  varieties  to  meet  and  resist  the 
several  directions  of  stress. 

The  line  of  greatest  mechanical  resistance  in  any  root  is  in  its  ver- 
tical axis,  and  is  the  only  line  of  stress  which  does  not  tend  to  displace 
the  tooth  mechanically.  As  to  the  vital  resistance  of  a  root,  this  rule 
is  but  partially  true,  for  roots  appear  to  rebel  against  stress  in  any  other 
direction  than  that  due  to  their  normal  anatomical  positions. 

In  normal  occlusion  the  stress  upon  any  individual  tooth  is  lessened 
or  modified  by  the  occlusion  of  the  other  teeth  of  a  denture,  so  that  the 
conditions  of  any  tooth  as  part  of  a  denture  are  not  those  of  the  same 
tooth  standing  alone.  For  example,  the  incisors  normally  receive  a 
stress  which  ceases  as  soon  as  the  molars  and  bicuspids  are  in  perfect 
contact;  in  the  absence  of  these  latter  teeth  the  entire  force  of  occlusion 
falls  upon  the  incisors,  and  they  are  unduly  strained. 

With  the  molars,  the  greatest  stress  being  vertical,  support  is  de- 
manded from  the  entire  root  area  underlying  the  crown.  The  latter 
represents  primarily  a  block  resting  firmly  upon  a  broad  base.  The 
lateral  stress  is  guarded  against  by  having  one  or  two  posts  in  the  axes 
of  the  roots  or  by  the  periphery  of  the  crown  grasping  that  of  the  root- 
walls. 

It  is  evident  that  the  crown  best  adapted  to  meet  these  stresses  is 
that  having  a  barrel  form,  grasping  firmly  the  periphery  of  the  root;  the 
retaining  cement  becomes  mechanically  part  of  the  tooth,  so  that  these 
crowns  rest  uniformly  upon  the  entire  area  of  the  root-face. 

Pin  crowns  of  the  variety  placed  upon  bicuspid  roots  are  occasionally 
employed  upon  molar  stumps,  but,  as  a  rule,  their  intrinsic  resistance  is 
not  as  great  as  that  offered  by  barrel  crowns. 

THE  FORMS   OF   THE  TEETH. 

The  great  consideration  as  a  governing  factor  in  the  placing  of  arti- 
ficial crowms  is  the  forms  of  the  teeth.     This  includes  the  shapes  and 


664  ARTIFICIAL   CROWNS. 

sizes  of  the  roots  to  be  crowned  as  factors  deterniiiiiii<i;  the  type   or 
variety  of  crown   selected. 

How  does  the  area  of  root-section  compare  witli  <lie  len(,nh  of  the  root  ? 
And,  again,  how  do  these  factors  compare  with  the  length  and  breadth 
of  the  occlusal  surface  of  the  artificial  crown?  For  example  two  roots 
may  have  the  same  length  and  the  same  sectional  area;  one  re(|uires  a 
crown  half  again  as  long  as  the  other  (Fig.  597),  or  the  stress  of  occlu- 
sion may  be  more  severe;  obviously,  the  mechanical  stress  upon  the 
root  is  increased  in  the  ratio  of  the  extent  of  its  occlusion  or  the  amount 
of  increased  leverage  represented  in  the  crown  of  greater  length.  Or, 
again,  two  roots  having  the  same  length,  and  artificial  crowns  of  the 
same  length  and  breadth,  but  the  sectional  area  of  the  face  of  one  root 
greater  than  that  of  the  other,  it  is  evident  that  the  resistance  afforded 
by  the  root  of  smaller  section  will  be  correspondingly  decreased.  A 
long  heavy  root  will  bear  safely  a  crown  which  if  set  upon  a  short  and 
narrow  root  and  subjected  to  an  equal  stress  would  result  in  the  loss  of 
the  root. 

PHYSIOLOGICAL  RELATIONS. 

Under  this  heading  are  considered  the  vital  conditions  of  the  tissues 
of  the  teeth  or  roots  and  of  their  sources  of  nutrition  and  support;  if 
the  pnlp  be  alive,  what  its  condition;  and  whether  it  is  possible  or  ad- 
visable to  place  an  artificial  crown  without  effecting  the  destruction  of 
that  organ.  Teeth  are  occasionally  broken  in  such  a  manner  as  to 
render  restoration  of  form  by  filling  material  inadvisable,  and  yet  not 
uncovering  the  pulp,  the  latter  being  healthy  and  the  dentine  normal. 
It  is  possible  in  some  of  these  cases  to  adjust  an  artificial  crown  without 
destroying  or  disturbing  the  pulp;  it  is  evident  that  modifications  of  the 
barrel  crown  are  alone  applicable. 

Next,  what  is  the  texture  of  the  dentine?     Highly  organized  dentine 

will  bear  safely  a  strain  which  would  injure  dentine  of  poorer  type.     The 

latter  type  of  tissue  is  non-resistant  to  the  progress  of 

Fig.  597         dental  caries,  and  thus  needs  protection  against    con- 

'.l.~~2Z.    tact  with  or  the  access  of  the  active  causes  of  caries. 

ii  The  condition  of  the  enamel    rarely    is  a  factor  in 

H|     the  plans,   except  that  faulty  enamel,  through  its  lia- 

Wl     bility  to  fracture  or    crumbling,   will    sooner  or  later 

I  /       leave  part  of  a  natural  crown  or  a  stump  for  the  atten- 

V        tion  of  the  prosthetist.    It  may  be  that   a  tooth  crown 

consisting  in  large  part  of  thin  and  discolored  enamel  is  removed    for 

aesthetic  considerations  and  replaced  by  an  artificial  crown. 

The  Condition  of  the  Pericementum. — This  includes  a  consideration 
of  the  existing  vital  relations  of  this  tissue,  and  the  possible  sources  of 
irritation  to  it  formed  by  the  placing  of  an  artificial  crown,  or  acting 
after  the  crown  is  set. 


PATHOLOQICAL  RELATIONS.  665 

PATHOLOGICAL  RELATIONS. 

As  teeth  which  require  artificial  crowns  have  been  brought  to  their 
condition  by  the  action  of  pathogenic  agencies,  which  if  unchecked 
will  ultimately  cause  the  loss  of  the  roots  themselves,  it  is  evident  that 
these  are  the  most  important  of  the  factors  requiring  attention. 

The  question  of  existing  pathological  conditions  and  their  treatment 
belongs  properly  to  the  province  of  dental  pathology  and  therapeutics; 
but  the  present  subject  is  the  common  ground  upon  which  the  therapist 
and  prosthetist  meet :  their  offices  are  the  two  steps  of  a  common  opera- 
tion. 

If  a  tooth  contains  a  vital  pulp,  and  it  is  designed  to  retain  that  organ, 
the  infected  dentine,  that  invaded  by  the  carious  process,  should  be 
removed  with  the  same  care  as  though  it  were  being  prepared  for  the 
reception  of  a  filling.  Should  the  pulp  be,  or  have  been  the  seat  of  in- 
flammation, it  is  destroyed  and  removed.  If  it  is  to  remain  alive,  the 
same  care  is  observed  in  guarding  it  against  thermal  shock  as  with  fill- 
ings, so  that  after  placing  an  artificial  crown  upon  a  stump  containing  a 
vital  pulp  there  should  be  no  increased  response  to  applications  of  heat 
or  cold. 

When  post  crowns  are  indicated  the  pulp  is  to  be,  necessarily,  de- 
stroyed. 

The  extent  to  which  the  carious  process  has  invaded  the  dentine  is  a 
large  factor  for  consideration ,  for  the  greater  the  loss  of  the  dentine  the 
weaker  the  root  becomes,  the  less  mechanical  resistance  it  affords,  so 
that  support  may  be  required  to  guard  the  weakened  structure  against 
fracture.  Again,  the  more  extensive  the  carious  process  the  greater  is 
the  probability  of  such  deep  infection  of  the  dentine  that  an  increased 
length  of  time  is  required  for  sterilizing  the  infected  tissue. 

The  present  condition  of  the  pericementum  and  its  past  history  are 
the  most  important  of  all  considerations.  It  is  possible  that  a  form  of 
crown  may  be  required  which  will  permit  of  ready  removal  in  case  of 
recurring  pericementitis;  however,  in  a  properly  treated  root  such  a 
contingency  should  be  a  remote  possibility. 

The  liability  or  disposition  of  the  pericementum  toward  inflammation 
may  enforce  a  lessening  of  the  stress  brought  to  bear  upon  it  through 
the  artificial  crown.  It  is  a  recognized  principle  of  surgery,  and  never 
to  be  lost  sight  of  in  crown  and  bridge-work,  that  a  part  once  inflamed 
has  an  increased  tendency  toward  subsequent  inflammation. 

It  is  an  inflexible  rule  that  before  the  setting  of  an  artificial  crown 
the  root  bearing  it  must  have  such  preliminary  treatment  that  its  pulp- 
canal  and  substance  of  its  dentine  are  rendered  aseptic,  and  if  possible 
antiseptic,  and  the  pericementum  must  be  brought  to  a  condition  of 
health. 

Unless  the  root  be  firmly  fixed  and  supported  by  sound  alveolar 
structures  the  following  operations  prove  abortive  just  in  the  degree 
that  the  root  is  the  subject  of  anatomical  or  physiological  perversion. 
It  must  be  remembered  that  the  setting  of  an  artificial  crown  places  be- 


666  ARTIFICIAL  CROWNS. 

3'ond  access  the  most  important  means  of  combatin<i;  disease  of  the 
crowned  root,  so  that  the  assurance  of  continued  root-heaUh  is  a  neces- 
sary preHminary. 

PREPARATION  OF  ROOTS. 

Under  this  heading  are  incUuled,  first,  the  therapeutic  measures 
necessary  to  secure  the  continued  heakh  of  all  the  dental  tissues  and 
their  supports;  and  next  the  mechanical  preparation  necessary  to  form 
the  root  into  a  resistant  base  to  which  a  crown  may  be  fitted  with  ex- 
actitude. 

PULP  DEVITALIZATION. 

When  for  any  reason  it  is  found  necessary  to  devitalize  the  pulp  of  a 
tooth  preparatory  to  the  placement  of  an  artificial  crown,  there  are 
several  questions  to  be  considered.  The  first  of  these  is,  in  which  of 
the  methods  that  may  be  employed,  is  there  the  least  danger  of  irrita- 
tion or  injury  to  the  retentive  structures  of  the  tooth  ?  Second,  in  what 
way  may  the  operation  be  done  w^th  the  least  pain  to  the  patient? 
Third,  how  can  it  be  most  quickly  and  easily  accomplished  ? 

There  are  several  methods  and  agents  employed  for  the  devitaliza- 
tion of  the  pulp  almost  any  of  which  may  be  indicated  under  certain 
conditions.  Among  the  agents  usually  employed  for  this  purpose, 
arsenic  is  easily  in  most  general  use.  It  is  the  one  which  requires  the 
greatest  care  in  its  use;  is  dangerous  in  unskilled  hands,  and  is  uncertain 
in  its  results  both  as  regards  pain  to  the  patient  and  effectiveness. 
When  its  use  has  been  decided  upon  the  method  advised  by  Dr.  James 
Truman  is  recommended,  and  it  will  seldom  be  attended  by  pain  if 
his  directions  are  carefully  followed.  A  very  small  quantity  of 
arsenious  acid  is  mixed  with  iodoform,  using  oil  of  cloves  or  carbolic 
acid  as  a  vehicle  and  applying  it  to  the  exposed  pulp  on  a  small  pel- 
let of  cotton.  This  is  covered  with  a  small  cap  of  tin  or  aluminum, 
to  prevent  pressure  on  the  pulp,  and  the  cavity  is  sealed  with  gutta- 
percha or  cement. 

If  the  arsenic  is  applied  directly  to  the  pulp,  it  should  be  left  in  for  a 
few  hours  only.  If  on  opening  the  tooth  again,  it  is  found  that  it  has 
not  taken  effect,  another  application  may  be  made  and  this  may  be  re- 
peated if  it  is  found  necessary  to  do  so.  The  action  of  the  arsenic 
should  not  be  permitted  to  extend  all  the  way  to  the  apex,  but  should  be 
watched  carefully  and  the  pulp  removed  while  there  is  still  some  life  at 
its  apical  extremity.  If  there  is  no  exposure  it  is  safer  to  make  the  ap- 
plication only  a  little  below  the  enamel,  or  in  the  bottom  of  an  exist- 
ing cavity,  just  sufficiently  deep  to  be  properly  sealed  in,  rather 
than  to  make  an  exposure.  The  arsenic  will  act  upon  the  dentine,  to 
desensitize  it,  so  that  in  a  few  hours  it  will  be  sufficiently  obtunded  to 
enable  the  operator  to  expose  the  pulp  without  pain  to  the  patient, 


PULP  DEVPFALIZATION.  667 

jit'ter  which,  if  he  so  desires,  he  can  anaesthetize  and  remove  the  pulp  by 
any  method  which  he  may  see  fit  to  employ. 

It  shoukl  always  be  borne  in  mind  that  arsenic  or  an  anaesthetic  will 
not  act  upon  an  inflamed  or  congested  pulp.  If  the  pulp  is  in  this  con- 
dition, a  dressing  of  oil  of  cloves  or  eugenol  and  sulphate  of  morphia  is 
one  of  the  best  apphcations  for  relieving  the  pain  and  reducing  the  in- 
flammation. A  pellet  of  cotton  is  saturated  with  the  oil  of  cloves  or 
eugenol  and  from  one-fortieth  to  one-thirtieth  of  a  grain  of  the  morphia 
is  added  to  it.  This  is  placed  in  the  ca\'ity  in  contact  with  the  pulp  and 
allowed  to  remain  until  the  pulp  is  quiescent,  which  will  usually  be  in 
from  tw^enty-four  to  forty-eight  hours,  after  which  the  arsenic  or  the 
anaesthetic  may  be  applied. 

It  is  good  practice  not  to  use  arsenic  if  it  can  possibly  be  avoided,  as 
there  is  always  a  chance  of  disturbances  following  its  use  such  as  arsen- 
ical pericementitis  or  even  necrosis.  The  former  of  these  may  not  man- 
ifest itself  immediately,  but  sooner  or  later  it  is  liable  to  appear  either 
in  a  mild  or  severe  form.  If  the  arsenic  is  not  sealed  in  perfectly, 
especially  if  the  ca^dty  extends  below  the  gingival  margin,  necrosis  is 
likelv  to  ensue,  which  in  some  cases  mig-ht  have  far  reaching;  effects. 
Some  patients  are  peculiarly  susceptible  to  this  poison ;  and  in  the  mouths 
of  such,  arsenic  applied  for  a  few  hours  only  would  be  sufficient  to  de\d- 
talize  the  pulp  completely,  while  in  others  it  might  remain  for  days  or 
even  weeks  with  seemingly  little  effect.  In  the  former  case,  if  it  were 
left  in  the  tooth  for  any  great  length  of  time,  the  chances  are  that  its 
action  w^ould  not  be  limited  to  the  pulp  itself,  but  would  extend  through 
the  foramen  and  beyond  the  apex  and  involve  the  surrounding  tissue. 
Especially  would  this  be  true  if  the  foramen  were  somewhat  enlarged. 
The  danger  would  be  greater  when  using  it  on  a  young,  than  on  an 
elderly  patient,  as  the  root  may  not  be  fully  developed,  and  the  foramen 
may  be  widely  patulous,  in  which  cases,  carbolic  acid,  creosote  or  some 
such  agent  is  indicated.  Cases  also  occur  in  which  there  is  an-imperfec- 
tion  in  the  walls  of  the  root-canals.  A  condition  of  this  kind  is  fortu- 
nately very  rare  as  it  is  one  which  it  is  impossible  to  foresee  and  guard 
against,  and  if  arsenic  is  used,  disturbances  which  may  result  in  serious 
injury  to  the  patient  are  unavoidable.  It  sometimes  happens  that  the 
pulp  will  resist  the  arsenic  and  repeated  applications  will  have  no  effect, 
in  which  event,  some  other  agent  must  be  employed. 

The  safest  and  most  rapid  method  is  immediate  devitalization  by 
surgical  means,  either  by  anaesthetizing  and  extirpating  the  pulp  at  once 
with  broaches,  or  by  driving  it  out  with  a  pointed  orange-wood  stick. 

In  employing  the  first  of  these  methods,  the  following  are  the  details 
of  the  operation. 

The  rubber  dam  should  be  applied  to  the  tooth  whenever  it  is  possible 
to  do  so.  If  this  cannot  be  done,  napkins  may  be  substituted  to  keep 
the  secretions  of  the  mouth  from  coming  in  contact  with  the  field  of 
operation.  If  a  cavity  exists  through  which  the  pulp  canals  are  acces- 
sible or  may  be  made  so,  it  should  be  utilized.  The  instruments  to  be 
used  should  be  ready  at  hand,  so  that  they  may  be  grasped  instantly  as 


668  ARTIFICIAL   CROWNS. 

soon  as  they  are  needed.  These  should  consist  of  broaches  for  remov- 
ing the  pulp  from  the  canals,  a  hirge  spear-pointed  (h-ill,  hirge  coarse  rose 
burs,  a  hirge  cross-cut  fissure  bur  and  one  or  two  sliarp  spoon  excava- 
tors. There  are  several  effective  instruments  of  the  syringe  type,  strongly 
made  and  capable  of  exerting  great  pressure  which  have  been  designed 
for  the  purpose  of  obtunding  or  devitalizing  with  cocaine,  but  in  the 
absence  of  one  of  these,  a  hand  instrument  and  a  piece  of  soft  rubber 
may  be  used.  The  softened  dentine  should  be  removed  from  the  cavity 
and  if  there  is  an  exposure  of  the  pulp,  a  crystal  of  cocaine  h)  drochlorate 
is  placed  immediately  over  it  and  a  small  pellet  of  cotton,  not  larger  than 
a  pin  head,  is  saturated  with  one  of  the  prepared  local  anaesthetic  solu- 
tions or  adrenalin  chloride  and  placed  over  the  cocaine.  A  solution  of 
cocaine  alone  will  render  satisfactory  results  but  seems  more  effective 
when  used  in  conjunction  with  some  other  drug.  A  solution  of  formalin 
one  part  and  alcohol  five  parts  used  with  the  cocaine  crystals  is  favor- 
ed by  a  good  many  operators.  A  piece  of  unvulcanized  rubber,  large 
enouo'h  nearly  to  fill  the  cavity,  is  put  over  the  cotton  and  a  burnisher 
or  other  instrument  which  nearly  fills  the  opening  of  the  cavity  is  used 
to  press  this  tightly  in,  the  pressure  being  kept  up  for  about  one  minute. 
If  the  pulp  is  freely  exposed,  the  anaesthetic  may  be  injected  directly  into 
it  with  a  hypodermic  syringe,  but  this  is  a  more  painful  operation  and 
possesses  no  advantage  over  the  method  just  described.  After  the  pulp 
is  completely  anaesthetized  and  the  rubber  and  cotton  have  been  re- 
moved, the  pulp-chamber  should  be  freely  opened  with  the  rose  or  fissure 
burs  so  that  there  will  be  direct  access  to  all  of  the  canals.  The  body  of 
the  pulp  may  then  be  cut  away  with  a  coarse  bur  or  a  spoon  excavator, 
after  which  that  in  the  canals  may  be  removed  with  broaches. 

If  it  is  a  sound  tooth  which  is  to  be  devitalized,  it  is  necessary  to  make 
a  cavity  for  the  exposure  of  the  pulp.  The  actual  exposure  need  be  no 
larger  than  the  point  of  a  needle.  In  any  of  the  six  anterior  teeth,  this 
opening  should  be  made  on  the  palatal  or  lingual  side,  just  above  the 
basilar  ridge  and  on  a  line  with  the  pulp  canal.  The  enamel  at  this 
point  is  very  thick  and  hard  and  can  best  be  broken  through  with 
small  corundum  or  carborundum  wheels  or  a  diamond  drill.  The 
bicuspids  and  molars  should  be  opened  through  the  fissures  and  on  a 
line  with  the  centre  of  the  tooth. 

After  breaking  through  the  enamel,  a  large  spear-pointed  drill  may 
be  used  to  open  into  the  pulp.  If  the  engine  is  running  rapidly  and  the 
drill  is  verv  sharp,  the  exposure  may  often  be  made  quickly  and  with 
very  little  discomfort  to  the  patient,  but  if  the  tooth  is  at  all  sensitive, 
the  drilling  should  be  stopped  as  soon  as  the  patient  experiences  pain 
and  the  cocaine  and  pressure  applied  in  the  manner  described  above. 
This  will  prove  an  excellent  obtundent  for  the  dentine  and  generally 
one  or  two  applications  will  enable  the  operator  to  open  directly  into 
the  pulp.  Another  application  can  then  be  made  to  completely  anaes- 
thetize it,  after  which  the  opening  may  be  enlarged  and  the  pulp  re- 
moved as  already  described. 

In  using  the  anaesthetic  with  pressure,  the  pulp  is  not  devitalized  of 


PVI.P  DK  VITA  LIZA  TION.  G69 

course,  but  simply  aui\isthetized,  aud  sensibility  may  return.  In  some 
of  the  multi-rooted  teeth,  where  difficulty  is  experienced  in  getting  into 
the  canals,  sensation  may  have  returned  to  the  pulp  in  one  or  two  of  them 
while  the  pulp  was  being  removed  from  the  others,  and  this  would 
necessitate  a  second  application;  but  generally  one  is  sufficient. 

Ethyl  chloride  may  also  be  used  in  making  the  exposure.  In  drilling 
the  cavity  when  the  tooth  begins  to  be  sensitive,  the  spray  should  be 
applied,  intermittently  at  first,  touching  the  tooth  only  for  an  instant, 
repeating  at  short  intervals,  each  time  keeping  it  on  for  a  little  longer 
period,  until  the  tooth  becomes  insensible.  In  this  way  the  tooth  is 
cooled  gradually  and  the  pain  or  shock  which  occurs  when  the  spray 
is  applied  directly  and  continuously  is  avoided.  The  spear-pointed 
drill  is  now  used  and  if  the  tooth  again  becomes  sensitive  before  the 
pulp  is  reached,  the  spraying  is  repeated. 

In  undertaking  to  remove  the  pulp,  the  operator  should  have  an  ac- 
curate knowlerlge  of  the  anatomy  of  the  teeth.  He  should  know  the 
number  of  roots  which  each  tooth  should  possess,  and  just  whereto  look 
for  the  entrance  to  the  canals  in  the  floor  of  the  pulp  chamber.  Fre- 
quently some  of  these  are  very  minute  and  hard  to  find,  and  a  knowledge 
of  their  normal  position  is  a  most  essential  requisite  in  the  search  for 
them. 

The  mesial  root  of  the  lower  molars  is  frequently  very  difficult  to 
open.  While  there  is  but  one  root,  in  nearly  every  case  there  are  prac- 
tically two  very  constricted  canals,  a  buccal  and  a  Hngual,  which  diverge 
or  run  parallel  as  they  open  from  the  pulp-chamber,  but  unite  at  or  near 
the  apex,  making  exit  by  a  single  foramen.  (Fig.  59S.)  It  is  some 
times  impossible  to  open  both  of  these  to  their  full  length,  but  every 
effort  should  be  made  to  get  at  least  one  of  them  clear  all  the  way  to  me 
end  of  the  root.  For  if  one  of  the  canals  is  opened  to  the  apex  and  the 
foramen  perfectly  closed  the  pulp  which  remains  in  the  other  canal  is 
entirely  cut  oft',  as  in  (Fig.  598,  A  and  B)  and  the  danger  of  subsequent 
trouble  from  it  is  very  remote. 

After  one  canal  is  filled,  the  remaining  canal  is  saturated  with  chloride 
of  zinc  and  filled  as  far  as  possible,   so   that    only   a    little 
thread  of  coagulated  pulp  tissue  is  left  in  the  root.  Fig.  593 

The  buccal  canals  of  the  upper  molars  also,  are  frequently 
so  small  that  it  is  very  hard  to  get  into  them  for  any  dis- 
tance. The  twisted  three  sided  broaches  of  the  Kerr  type 
are  excellent  for  enlarging  these  constricted  canals.  A  drop 
of  sulphuric  acid  will  very  often  materially  assist  the  oper- 
ator in  opening  them. 

In  teeth  where  the  ends  of  the  roots  are  bent  almost  if  not  quite  at 
right  angles  to  the  rest  of  the  root,  it  is  impossible  to  remove  all  of  the 
pulp.  As  much  of  this  tissue  as  possible  should  be  removed  with 
broaches,  following  these  with  sodium  and  potassium  or  sodium  dioxide, 
after  which  a  dressing  of  one  of  the  essential  oils  and  aristol  or  iodoform 
may  be  placed  in  the  canal  which  may  be  filled  at  a  subsequent  sitting 

Occasionally  the  tooth  may  possess  more  or  less  roots  than  the  nor- 


670  ARTIFICIAL  CROWNS. 

mal  number.  In  every  case  the  pulp-chamber  should  be  well  opened 
and  the  floor  and  sides  should  be  carefully  examined  with  a  fine  explorer 
for  the  aperture  of  the  canals.  It  is  a  mistake  to  undertake  to  remove 
the  pulp  with  only  a  small  openinjij  in  the  crown  of  the  tooth,  especially 
if  it  is  to  be  crow^ied.  It  does  not  weaken  it  to  open  it  to  the  full  size 
of  the  pulp  chamber,  as  the  crown  of  the  tooth  is  only  as  strong  as  that 
part  which  has  the  least  sectional  area  and  this  is  at  or  near  the  floor  of 
the  pulp  chamber,  (Fig.  599,  A),  consequently  the  opening  may  be  made 
to  the  full  size  of  the  floor  of  the  pulp  chamber  without  weakening  the 
tooth  in  the  least. 

The  third  molars  are  especially  lacking  in  uniformity  as  to  the  num- 
ber of  their  roots,  and  the  canals  are  frequently  so  small  and  tortuous  as 
to  render  it  impossible  to  open  them  more  than  a  short  distance.  In 
such  cases  the  operator  must  be  satisfied  with  something  less  than  the 
ideal  results  which  he  would  desire  so  far  as  filling  them  to  the  end  is 
concerned,  but  he  should  always  be  assured  that  they  are  at  least  per- 
fectly sterile. 

In  employing  the  heroic  method  of  pulp  extirpation,  the  pulp  must  be 
well  exposed.  The  end  of  an  orange-wood  stick  is  whittled  to  about 
the  size  and  shape  which  the  canal  of  the  tooth  is  known  to  have,  bring- 
ing the  end  down  to  a  sharp  point.  It  is  laid  within  convenient  reach, 
together  with  a  small  leaded  mallet.  If  the  crown  of  the  tooth  is  to  be 
removed,  it  may  be  cut  nearly  through  by  making  a  groove  labially  and 
lingually  with  a  thin  disk  and  then  it  is  nipped  off  with  excising  forceps, 
using  a  chloride  of  ethyl  spray  if  the  tooth  is  very  sensitive.  If  there  is 
not  sufficient  exposure,  the  opening  may  be  enlarged  with  a  spear- 
pointed  drill  or  a  bud-shaped  bur.  The  point  of  the  orange-wood 
stick  is  then  dipped  in  carbolic  acid  and  placed  at  the  entrance  of  the 
canal  and  a  quick,  sharp  blow  given  it  with  the  mallet.  If  it  has  been 
properly  shaped,  the  pulp  will  be  forced  out  of  the  canal  beside  the 
stick,  or  will  be  found  clinging  to  it  when  the  latter  is  withdrawn.  If 
this  does  not  occur  and  any  of  the  pulp  remains  in  the  canal,  it  may  be 
removed  with  the  broach.  The  canal  is- then  cleansed,  sterilized  and 
filled.  This  method  is  especially  applicable  to  the  single 
iG.  599  rooted  teeth,  but  it  may  be  successfully  applied  to  the  first 
bicuspids  and  under  favorable  conditions,  even  to  molars 
wiiose  crowns  are  so  badly  broken  down  as  to  render  the 
canals  easily  accessible.  In  the  upper  molars,  if  the  body 
of  the  pulp  has  been  removed,  that  portion  in  the  pal- 
atal canal  may  almost  always  be  removed  in  this  way,  but 
the  buccal  canals  are  generally  too  small  and  difficult  of 
access.  In  the  lower  molars,  the  pulp  in  the  distal  root  canal  may  be 
extracted,  but  in  the  mesial,  there  would  be  the  same  trouble  as  in  the 
buccal  canals  of  the  upper  molars. 

If  properly  performed,  this  operation  is  as  nearly  painless  as  any 
method  of  devitalization.  It  is  done  so  quickly  that  the  pulp  is  par- 
alyzed by  the  shock,  and  the  pain  should  be  no  greater  than  that  felt 
from  the  slight  prick  of  a  pin.      This  happy  result  depends  entirely 


FILLING   OF  ROOT  CANALS.  671 

upon  the  manner  in  which  the  operation  is  done,  for  at  the  hands  of  an 
awkard  manipulator  it  might  cause  the  patient  a  great  deal  of  pain. 

It  has  been  the  practice  of  some  to. devitalize  the  pulp  in  this  manner 
and  to  fill  the  apex  at  the  same  time.  The  orange-wood  stick  is 
whittled  to  a  fine  point,  and  at  a  distance  of  from  one-eighth  to  three- 
sixteenths  of  an  inch  from  the  end,  a  cut  is  made  nearly  through  its 
substance  with  a  sharp  knife.  The  pulp  is  freely  exposed,  the  point  of  the 
stick  dipped  in  carbolic  acid  and  driven  quickly  into  the  canal  so  as  to 
wedge  the  end  tightly  in  the  apex.  The  stick  is  then  twisted  to  break  it 
off  at  the  point  at  which  it  has  been  cut,  leaving  the  apex  filled  with  the 
orange-wood.  It  is  very  questionable  if  this  is  good  practice.  In  the 
first  place,  the  wood  being  pervious  to  moisture  does  not  make  a  suitable 
filling  material  unless  it  is  first  saturated  with  some  solution  which  will 
make  it  positively  impervious.  Again,  should  the  foramen  happen  to 
be  enlarged,  the  point  might  easil}'  be  driven  through  and  beyond  the 
apex,  where  it  would  act  as  an  irritant  and  probably  eventually  be  re- 
sponsible for  an  alveolar  abscess.  Another  objection  to  this  method  is 
the  uncertainty  of  reaching  the  extreme  apex  with  the  pointed  stick  if 
the  canals  happen  to  be  small  and  tortuous.  In  such  a  case  the  whole 
of  the  pulp  would  not  be  removed  and  the  portion  remaining  in  the  canal 
beyond  the  filling  might  cause  future  trouble,  and  if  the  canals  are 
tortuous,  it  would  be  impossible  to  remove  the  filling  for  treatment. 

FILLING  OF  ROOT  CANALS. 

Satisfactory  and  permanent  results  in  the  filling  of  pulp  canals  is  not 
so  much  a  matter  of  the  materials  employed  as  it  is  the  manner  in 
which  these  latter  are  inserted.  Of  course,  some  of  the  materials  in  use 
are  better  than  others,  and  it  is  probable  that  gutta-percha  and  ox}*- 
chloride  of  zinc  are  the  best. 

An  excellent  method  of  filling  with  gutta-percha  is  as  follows.     As  a 
preliminary  measure  to  the  operation  it  is  understood  that  the  rubber 
dam  is  to  be  applied  to  the  tooth  if  this  is  possible,  and  if  not,  napkins 
are  to  be  used  to  keep  the  field  of  operation  dry.   After  the  canal  has  been 
thoroughly  cleansed  and  dried,  a  gutta-percha  point  is  selected, 
of  a   size  corresponding  to  that  of  the  canal  to  be    filled,     Fig.  eoo 
and  fastened  to  the  end  of  a  canal  plugger  by  heating  the 
point  of  this  instrument.     A  little  oil  of  eucalyptus  is  intro- 
duced into  the  canal  from  the  points  of  a  pair  of  pliers  or 
with  a  wisp  of  cotton  twisted  around  a  broach.     The  gutta- 
percha point  is  now  dipped  into  oil  of  eucalyptus  and  then 
the  tip  of  it  into  iodoform  or  aristol,  after  which  it  is  placed 
in  the  canal  and  worked  into  it  with  a  pumping  motion,  car- 
rying it  farther  up  as  the  oil  softens  the  gutta-percha,  until 
it  becomes  loosened  from  the  plugger  and  is  packed  tightly  into  the 
root.     In  this  way  the  canal  can  be  as  thoroughly  filled  all  the  way 
to  the  apex  as  by  any  method.     It  does  no  harm  if  the  patient  winces 
a  little  during  the  operation,  as  that  is  a  pretty  good  indication  that 


672  ARTIFICIAL  CROWNS. 

the  end  of  the  root  has  been  reached.  Chloroform  may  be  used  in  place 
of  the  eucalyptus,  but  the  oil  is  preferable  as  it  is  of  a  heahng,  sooth- 
ing nature,  besides  possessing  antiseptic  properties  which  persist  in  the 
canal  for  many  years. 

If  the  foramen  is  enlarged,  care  must  be  used  not  to  force  the  filling 
beyond  the  apex.  A  canal  plugger  should  be  used  which  is  large  enough 
to  wedge  in  the  canal  while  it  is  still  about  one-eighth  of  an  inch  from 
the  apex  and  the  size  of  the  point  carefully  judged  so  as  to  fill  just  to 
the  end  of  the  root.  (Fig.  600.)  When  the  canal  has  been  enlarged  to 
receive  a  pin,  a  short  point  is  attached  to  the  plugger,  dipped  in  the 
eucalyptus  and  iodoform  or  aristol,  carried  to  the  apex  and  packed 
tightly  against  the  shoulder  left  by  the  reamer. 

When  chloro-percha  is  used  as  a  filler,  a  little  iodoform  or  artisol  is 
first  put  in  the  canal  and  the  chloro-percha  pumped  in  with  a  broach, 
a  fresh  supply  being  added  as  the  chloroform  evaporates.  When  it  is 
carried  well  into  the  canal  a  gutta-percha  point  may  be  forced  into  it, 
or  fine  wisps  of  cotton  may  be  packed  in  with  a  small  plugger,  until 
the  canal  is  filled.  It  is  questionable  if  this  will  make  as  perfect  a 
filling  as  the  gutta-percha  point,  especially  in  the  upper  teeth. 

The  objection  to  oxychloride  of  zinc  as  a  root  filling  is  the  irritating 
nature  of  the  zinc  chloride  and  the  difficulty  of  limiting  its  action.  If  a 
Uttle  of  'it  is  carried  beyond  the  apex,  it  will  cause  considerable  pain 
and  discomfort  to  the  patient,  and  may  sometime  result  seriously.  An- 
other objection  to  using  oxychloride  alone,  especially  in  any  of  the  teeth 
anterior  to  the  molars,  is  the  difficulty  of  opening  up  the  canals  at  some 
future  time  for  the  reception  of  a  pin,  should  it  become  necessary  to 
crown  the  roots.  This  difficulty,  however,  may  be  overcome:  after 
the  canal  has  been  pumped  full  of  liquid  cement,  a  gutta-percha  point 
is  inserted  and  forced  to  the  end  of  the  root. 

Paraffin  is  also  used  as  a  root  filler.  A  little  iodoform  or  aristol  is 
first  placed  in  the  canal  and  the  paraffin  carried  into  it  with  a  fine  heated 
broach.     This  makes  a  good  root  filling,  especially  in  the  lower  teeth. 


PERFORATED  ROOTS. 

This  IS  a  difficulty  which  is  frequently  encountered,  and  the  treat- 
ment of  it  is  often  very  puzzling  to  the  dentist.  Where  the  per- 
foration is  at  the  apex,  it  may  be  treated  and  the  root  filled  in  the  same 
way  as  an  abscessed  tooth  where  the  foramen  has  been  enlarged.  If 
there  has  been  much  inflammation,  a  dressing  of  one  of  the  essential 
oils  and  iodoform  or  artisol  may  be  kept  in  the  canal  until  the  soreness 
has  passed  away,  when  the  root  may  be  filled  in  the  manner  already  de- 
scribed. Where  the  perforation  is  of  long  standing,  the  root  will  prob- 
ably l)e  abscessed  and  the  treatment  of  the  case  would  come  under  the 
head  of  alveolar  abscess. 

Where  the  perforation  is  at  the  side  of  the  root,  it  is  cjuite  likely  that 
the  soft  tissues  have  grown  into  the  cavity.     This  intruding  tissue  may 


FRACTVRED  ROOTS.  673 

1)0  reinoveil  by  excision,  i)r  it  may  he  cauterized  with  triciii(jract'tic  acid, 
carbolic  acid  or  iodine.  Where  the  size  of  the  growth  is  not  great,  the 
opening  may  be  cleared  by  packing  the  pulp  cavity  tightly  with  dry 
aljsorbent  cotton.  This  will  expand  as  it  becomes  moist  and  force  the 
gum  tissues  out.  The  sides  of  the  opening  should  now  be  grooved  or 
roughened  so  as  to  hold  the  filling  in  place,  and  the  cavity  is  then  wiped 
out  with  adrenalin  chloride.  If  the  perforation  is  not  far  Ijelow  the 
gum  margin,  it  often  happens  that  a  small  flat-ended  instrument  mav  be 
passed  under  the  gum  and  up  the  side  of  the  root  so  as  to  cover  the  open- 
ing. If  this  be  possible  the  instrument  is  held  in  place  against  the  root, 
the  cavity  diied  thoroughly,  and  the  filling  packed  tightly  against  the 
instrument. 

Wliere  the  perforation  is  so  far  beyond  the  gum  line  that  it  is  not  pos- 
sible to  cover  it,  a  little  base-plate  or  high  heat -^gutta-percha  is  pressed 
into  it  and  then  removed.  This  will  show  the  exact  size  and  shape  of 
the  perforation.  If  gutta-percha  is  to  be  used  to  stop  it,  the  trial  plug 
is  trimmed  so  that  it  will  come  not  C|uite  to  the  outer  wall  of  the  root, 
lea^^ng  a  slight  excess  on  the  inside.  Adrenalin  chloride  will  prevent 
blood  or  moisture  from  oozing  into  the  cavity,  which  should  be  dried 
with  alcohol  and  then  wiped  out  with  oil  of  eucalyptus  or  any  other  es- 
sential oil.  The  plug,  which  has  previously  been  lightly  fastened  to 
the  end  of  an  instrument,  is  then  placed  in  the  opening  and  packed 
flush  with  the  canal  wall. 

Copper  amalga^m  is  one  of  the  best  filling  materials  for  cases  of  this 
kind.  In  the  one  just  described,  the  trial  plug  will  show  the  amount 
which  it  will  be  necessary  to  use  and  the  amalgam  is  packed  into  the 
opening,  care  being  used  not  to  force  it.  beyond  the  outer  wall  of  the 
root. 

Where  there  is  a  large  perforation  in  the  floor  of  the  pulp  chamber,  it 
is  better  first  to  cover  it  with  a  piece  of  thin,  soft  platinum  and  then  to 
fill  the  chamber  \\\\h.  copper  amalgam,  keeping  the  entrance  to  the 
canals  free. 

FRACTURED  ROOTS. 

This  is  a  troublesome  condition  of  somewhat  frequent  occurrence, 
and  it  is  often  difficult  to  decide  whether  a  root  which  has  been  split  can 
be  saved  or  will  have  to  be  extracted.  The  fracture  of  a  root  is  often 
brought  about  by  crowning  without  banding  it  and  is  most  frequently 
either  that  of  an  incisor  or  a  bicuspid.  In  the  majority  of  cases  where 
there  is  a  bad  fracture  it  will  be  necessary  to  remove  the  root  but 
sometimes  it  can  be  made  to  do  good  service  for  a  number  of  years 
even  if  it  has  been  split  all  of  the  way  to  the  apex.  Where  the  root  has 
been  newly  fractured  and  the  gum  tissue  has  not  had  time  to  crowd  its 
way  between  the  broken  parts,  they  should  first  be  drawn  close  together 
by  placing  a  strong  wire  of  30  or  32  gauge  over  the  stump  and  twisting 
it  tightly  in  the  same  way  as  in  taking  the  measurement  for  a  band.  It 
should  be  forced  up  on  the  root  as  far  as  possible  and  if  necessary,  the 
43  .  ' 


674  ARTIFICIAL  CROWNS. 

gum  can  be  slit  on  the  labial  side  to  allow  of  its  being  carried  to  a  suffi- 
cient distance  under  the  gum.  The  root  can  then  be  prepared,  a 
tightly  fitting  band  made,  and  the  crown  constructed  and  cemented 
to  the  root.  After  the  cement  has  thoroughly  hardened,  the  wire  lig- 
ature is  to  be  cut  away,  and  if  the  band  has  been  properly  fitted,  the 
tooth  should  last  for  many  years. 

Another  way  to  preserve  these  roots  is,  after  the  parts  have  been 
drawn  together,  to  cement  a  narrow  iridio-platinum  band  on  the  root, 
then  to  proceed  to  make  the  crown  as  if  the  root  were  perfectly  sound. 

In  many  cases  where  there  is  only  a  minor  fracture,  the  part  which  is 
broken  away  may  be  removed  and  the  band  carried  beyond  the  line  of 
fracture. 


TREATMENT   OF  CONDITIONS  RESULTING   FROM   INFECTION 
OF   THE   PULP. 

If  the  pulp  be  the  seat  of  purulent  inflammation  or  of  moist  gangrene, 
it  should  be  removed,  so  that  none  of  the  pathogenic  organisms  may  be 
forced  into  the  tissues  about  the  apex.  The  root  and  the  degenerated 
pulp-tissue  are  filled  with  a  strong  penetrating  antiseptic,  such  as 
meditrina  (a  solution  of  hypochlorites),  and  this  is  permitted  to  exercise 
its  properties  before  the  broach  is  applied.  It  is  a  wise  precaution  to 
wash  the  mouth  well  with  this  solution  prior  to  opening  any  pulp-cham- 
ber in  which  there  is  putrescible  material.  When  possible,  the  rubber 
dam  is  applied,  the  cavity  dried,  and  a  strong  solution  of  sodium  per- 
oxide carried  into  the  canal,  gently  stirring  it  with  an  iridio-platinum 
broach:  as  soon  as  effervescence  ceases,  wash  out  the  canal  with  sterilized 
water,  and  repeat  the  applications  of  the  peroxide  until  access  is  had 
to  the  apex  of  the  root. 

The  dentine  of  roots  which  have  contained  gangrenous  pulps  is  the 
seat  of  more  or  less  albuminous  decomposition,  so  that  ample  time 
should  be  taken  in  sterilizing  it.  Sodium  peroxide,  is  the  agent  to  be 
preferred,  as  this  substance  is  itself  decomposed  into  sodium  hydrate  and 
free  oxygen ;  the  former  saponifies  the  fatty  products  of  decomposition 
and  dissolves  the  protoplasmic  filaments;  the  oxygen  mechanically 
drives  out  the  dissolved  materials,  and  effectually  destroys  any  or- 
ganisms present. 

If  there  be  no  exudation  from  the  apical  tissues  into  the  canal,  it  is 
good  practice  to  dry  out  the  canal  by  means  of  alcohol  and  hot  blast, 
and  fill  the  apical  portion  of  the  canal  with  a  gutta-percha  cone  which 
has  been  covered  by  an  antiseptic  oil — cajuput,  cinnamon,  cassia,  or 
eucalyptus,  and  then  dipped  into  aristol  or  iodoform. 

Should  the  apex  of  the  root  be  the  seat  of  an  abscess,  this  is  to  be  cured 
before  the  apical  foramen  is  sealed.  The  canal  is  washed  out  with 
the  sodium  peroxide,  and  cleansed  thoroughly :  no  harm  is  done  if  the 
solution  be  forced  through  the  root.  Succeeding  this,  a  solution  of  caus- 
tic pjrozone  is  pumped  through  the  canal  into  the  abscess-sac  until  the 


ABSCESSED  ROOTS 


Q71 


pus  is  driven  through  the  fistula.  As  a  rule,  these  roots  may  be  filled 
at  once,  and  the  abscess-sac  is  soon  obliterated  by  the  formation  of  new 
tissue  about  the  apex  of  the  root.  It  occasionally  happens  that  the  fistula 
does  not  close  after  one  injection,  so  that  as  a  precautionary  measure 
the  permanent  hermetical  sealing  of  the  apex  of  the  canal  is  deferred 
until  it  is  seen  that  the  fistula  heals  and  the  normal  color  of  the  gum  over 
the  affected  tooth  is  restored. 

Cases  present  at  times  which  give  a  history  of  a  fistula  alternately 
healing,  then  opening.  Even  after  repeated  injections  the  fistula  will 
open  periodically,  and  a  discharge  of  pus  or  serum  occur.  A  condition 
is  present  at  the  apex  of  the  root  which  demands  removal  by  amputa- 
tion of  the  apex.  Before  the  pus  formed  at  the  apex  of  a  root  makes  its 
escape  through  a  fistulous  opening  in  the  gums  the  destruction  of 
tissues  incidental  to  or  characteristic  of  abscess  proceeds  in  all  directions, 
so  that  by  the  time  a  fistula  is  established  the  end  of  the  root  is  extend- 
ing into  an  irregular  cavity,  the  pericementum  destroyed  for  some  dis- 
tance above  the  apex,  and  the  uncovered  portion  of  the  cementum 
saturated  with  noxious  material.  When  the  pus  above  the  dotted  line 
(Fig.  601)  discharges,  the  fistula  may  heal,  and  remain  closed  until  an 
increased  pus-formation  again  re-estabhshes  the  fistula. 

The  gum  is  to  be  divided  above  the  apex  of  the  root,  the  pericemen- 
tum is  scraped  from  a  small  area,  and  free  entrance  is  gained  to  the 
abscess-cavity  by  means  of  sterilized  burs.  As  soon  as  the  bleeding  is 
checked  a  fissure  bur  is  passed  through  the  opening  and  the  denuded 
portion  of  the  root  cut  off  and  rounded.  The  sterilization  of  the  canal 
and  its  filling  have  preceded  the  amputation. 

In  what  are  known  as  blind  abscesses,  those  without  a  fistulous  tract 
leading  from  them  and  discharging  externally,  it  is  ad\asable  where 
possible  to  make  an  artificial  fistula.  The  mouth  is  sterilized  and  a 
crystal  of  cocaine  placed  on  the  gum  over  the  apex  of  the  root.  The 
length  of  the  root  is  measured  by  a 
broach  in  the  canal,  and  this  length 
measured  on  the  gum  over  the 
root.  A  crucial  incision  is  made 
through  the  gum,  the  bone  denuded 
of  periosteum  over  a  small  area,  and 
a  spear-pointed  engine  drill  is  quickly 
passed  through  the  bone  and  into 
the  abscess-ca^dty .  The  case  is  treat- 
ed then  as  a  simple  abscess.  The 
operation  may  be  made  almost  pain- 
less by  injecting  a  few  minims  of  a 
4  per  cent,  solution  of  cocaine.  The  canal  is  filled  after  a  thorough 
sterilization,  and  pending  the  healing  of  the  abscess-cavity,  the  external 
opening  is  kept  patulous  by  means  of  a  couple  of  strands  of  floss  silk 
acting  as  a  tent  and  means  of  drainage. 

Persistent  endeavor  should  be  made  to  enter  freely  and  cleanse  out 
perfectly  to  the  apex  all  the  fragments  of  pulp-tissue  in  the  roots  of 


Fig.  601 


676  ARTIFICIAL   CROWyS. 

teeth,  even  in  the  most  minute  canals.  The  introduction  of  the  use  of 
sulphuno  acid,  in  connection  with  broaches,  for  gainino;  entrance  to, 
enhirgino;,  and  cleansing  canals,  by  Dr.  J.  11.  Callahan  ',  has  added  to 
the  operations  of  dentistry  a  most  valuable  expedient,  and  furnishes 
a  means  for  the  removal  of  a  common  cause  of  apical  pericementitis, 
imperfect  removal  of  pulp-fragments.  A  drop  of  a  50  per  cent,  solution 
of  sulphuric  acid  is  placed  over  the  mouth  of  a  fine  canal,  and  pumped 
into  it  by  means  of  a  fine  Donaldson  })roach. 

INIuch  patience  will  be  required  to  effect  the  desired  end  in  some 
teeth,  but  so  long  as  there  is  an  imperfectly  cleansed  canal  there  is  the 
ever-present  fear  of  the  possibility  of  abscess,  and  if  the  crown  be  prop- 
erly set,  it  is  most  difficult  to  cure  the  diseased  condition. 

Roots  or  teeth  which  have  a  portion  of  Iheir  surface  overgrown  by 
a  hypertrophied  gum-tissue  must  have  the  latter  removed,  so  that  the 
field  of  operation  may  be  open.  If  it  be  a  pendulous  mass,  the  gum  is 
excised  sufficiently  to  free  the  root  outline.  If  the  margins  of  the  root 
be  covered  by  the  gum,  it  is  to  be  pressed  back  until  the  field  of  opera- 
tion is  free.  The  canal  and  the  pockets  beneath  the  gum  margins  are 
washed  out  with  meditrina  and  the  canal  and  face  of  the  root  dried.  A 
block  of  temporary  stopping  is  made  and  formed  into  a  truncated  cone, 
the  small  end  of  which  is  pressed  against  the  face  of  the  root  and  the 
mass  is  flattened  so  that  it  presses  the  gum  away  from  the  root  on  all 
sides.  "Should  there  not  be  sufficient  concavity  in  the  root  to  hold  the 
stopping,  a  large-headed  carpet  tack  may  l)e  pressed  into  the  canal  and 
the  gutta-percha  wedge  built  around  the  post.""^ 

MECHANICAL  PREPARATION  OF  TEETH  AND  ROOTS. 

The  vital  relations  of  the  teeth  or  roots  having  been  satisfactorily 
settled,  the  success  of  either  crowns  or  bridges  depends  more  largely 
upon  the  proper  preparation  of  their  abutments  than  upon  any  other 
mechanical  factor.     If  these  are  not  properly  prepared,  the  results 
will  be  disappointing  to  both  dentist  and  patient,  however  well 
Fig.  602     the  prostlictic  portion  of  the  work  is  done.     A  large  propor- 
tion of  failures  may  be  traced  to  this  source  and  too  much 
Ocare  and  study  cannot  be  given  to  the  subject.      Other  parts 
of  the  work  might  perhaps  be  slighted  without  seriously  affect- 
ing the  permanency  of  the  operation,  but  lack  of  proper  pre- 
paration of  the   abutments  will  aways  be  at  the  expense  of 
the  permanence  and  safety  of  the  fixture.     The  trimming  of  a  tooth 
may  seem  to  be  a  simple  operation,  but  it  is  not.     It  takes  time  to  do  it 
properly  and  this  time  must  be  given. 

We  shall  undertake  to  describe  in  detail  the  preparation  of  the  teeth 
and  shall  begin  with  those  which  are  to  recei\e  full  gold  crowns,  either 

'  Dental  Cosmos,  vol.  xxxvi.,  p.  329. 
2  W.  H.  Truoman. 


MECHANICAL  PREPARATION  OF  TEETH  AND  ROOTS.        677 

single,  or  as  abutment  pieces  for  briilge-work.     Wc  sliall  take  first  the 
lower  molars. 

Viewed  from  the  buccal  side  the  approximal  contour  of  these  teeth 
is  very  great.  Starting  just  below  the  gum  line,  it  swells  outward, 
until  at  the  point  of  contact  with  the  adjoining  teeth,  the  tooth  is  from 
one-quarter,  to  one-third  larger  tlian  at  the  neck,  ^'iewed  from  the 
occlusal  surface,  the  tooth  is  oblong  in  shape. 

This  tooth  when  properly  trimmed,  is  nearly  square  in  shape,  with 
the  corners  rounded,  being  slightly  broader  on  the  mesial  side  and 
nearly  flat,  while  on  the  distal  side,  it  is  somewhat  convex.  This  is 
owing  to  the  difference  in  the  size  and  shape  of  the  two  roots.  The 
buccal  and  lingual  sides  are  nearly  straight  lines,  with  a  slight  depres- 
sion near  the  middle,  from  the  bifurcation  of  the  roots.  (Fig.  602.) 
This  description  will  apply  more  especially  to  the  first  and  second 
molars,  the  third  molar  being  subject  to  greater  variation  in  shape  than 
the  others. 

The  lower  molars  are,  perhaps,  the  mvost  difficult  teeth  in  the  mouth 
to  trim.  The  bulk  of  the  cutting  in  these,  as  in  all  of  the  teeth,  will  be 
on  the  mesial  and  distal  surfaces,  the  contour  being  greatest  at  these 
points.  This  contour  must  be  entirely  removed  to  a  point  about  one- 
sixteenth  of  an  inch  below  the  gum  line,  so  that  when  the  band  is 
passed  over  them,  it  will  hug  the  neck  of  the  tooth  tightly.  For  doing 
this  work  cup  or  saucer-shaped  disks,  either  diamond,  or  thin  corundum, 
or  carborundum  and  rubber,  are  best  adapted.  (Fig.  603.)  The  tooth 
is  examined  with  an  explorer  to  determine  how  much  of  the  contour  it  is 
necessary  to  remove.  The  edge  of  the  wheel  is  placed  at  the  proper 
point  on  the  occlusal  surface  and  the  whole  of  the  contour  is  to  be  taken 
away  with  one  cut,  using  plenty  of  water  and  holding  the  wheel  very 
steady.  (Fig.  604.)  If  it  is  found  that  there  is  still  some  projection 
at  the  cervical  margin,  it  may  be  removed  with  the  face  of  the  wheel. 

For  the  buccal  and  lingual  sides,  when  using  the  straight  hand-piece, 
a  thin  flat  disk,  or  an  inverted  cone,  either  of  diamond  or  carborundum, 
may  be  used.  These  should  be  from  three-eights  to  five-eights  of  an 
inch  in  diameter. 

The  most  of  the  cutting  here,  will  be  on  the  lingual  side,  as  these 
teeth  generally  incline  toward  the  tongue.  The  trimming  of  these 
surfaces  may  be  most  easily  done  from  the  side  on  which  the  tooth  to  be 
trimmed  is  located.  If  it  is  on  the  right,  the  operator  should  stand  on 
that  side,  if  it  is  on  the  left,  he  should  stand  at  the  left  of  the  patient. 
The  buccal  side  may  be  ground  with  the  face  and  the  lingual  with  the 
reverse  side  of  either  the  flat  wheels,  or  inverted  cones.  (Figs.  605, 
606.) 

The  anterior  buccal  corner  may  be  nicely  rounded  to  the  desired 
distance  under  the  gum,  with  the  inverted  cone  or  disk,  using  the  face 
and  rotating  from  side  to  side  as  in  Fig.  605.  The  posterior  lingual 
corner  is  reached  with  the  reverse  side  of  the  same  wheels  (Fig.  607), 
while  for  the  posterior  buccal,  the  inverted  cone  must  be  used  from 
the  opposite  side  of  the  mouth. 


678 


ARTII'WIAL   CRO  WWS. 
Fig.  603 


Fig  604 


Fig.  605 


Fig.  606 


Fig.  607 


Fig.  608 


MECHANICAL  PREPARATION  OF  TEETH  AND  ROOTS.        679 

The  anterior  lingual  corner  is  the  most  difficult  of  any  to  reach,  but 
most  of  this  may  be  taken  away  with  the  face  side  of  a  saucer-shaped 
wheel,  rotating  it  from  the  opposite  side  of  the  mouth.  (Fig.  608.) 
^'ery  coarse  emery-cloth  disks  on  account  of  their  flexibility  are  of 
great  use  in  finishing  these  corners. 

AVith  the  right  angle  hand-piece,  small  diamond  disks  from  three- 
eighths  to  five-eighths  of  an  inch  in  diameter  will  be  found  very  useful, 
especially  for  the  corners.  In  some  places  which  cannot  be  reached 
with  wheels  or  disks  the  corners  or  ledges  may  be  removed  with  enamel 
cleavers  or  scalers.  The  No.  3  S.  S.  W.  scaler,  or  the  same  scaler  with 
one  safe  edge,  made  in  rights  and  lefts,  may  be  used.  The  explorer 
should  be  constantl}-  employed  to  detect  the  sHghtest  irregularity  or 
projection  of  the  surface  by  sliding  it  down  the  face  of  the  tooth,  and  the 
least  shoulder  or  ledge  must  be  removed,  so  that  when  the  band  is  passed 
over  the  tooth  and  under  the  free  margin  of  the  gum,  it  will  hug  the  neck 
tightly.  A  fissure  bur  or  a  finishing  bur  may  often  be  used  to  advan- 
tage for  locations  which  it  is  almost  impossible  to  reach  with  any  thing 
else. 

In  the  low^er  jaw  where  the  first  molar  has  been  lost,  it  will  generally 
be  found  that  the  second  has  pitched  forward  so  that  its  only  point  of 
contact  with  the  upper  teeth  is  at  one  of  the  distal  cusps.  In  cases  of 
this  kind  there  will  be  little  or  no  cutting  on  the  distal  side  of  the  tooth : 
but  on  the  mesial  side  at  the  masticating  surface,  it  would  be  necessary 
to  cut  far  back  tow^ard  the  centre  of  the  tooth  in  order  to  make  it  nearly 
parallel  \^dth  an  anterior  abutment  as  in  (Fig.  609.)  The  cup-shaped 
disks  are  used  here  as  in  the  former  cases.  The  lingual  and  buccal 
sides  and  the  corners  are  to  be  treated  in  a  manner  already  described. 

Where  there  is  an  excessive  leaning  of  the  tooth  toward  the  tongue, 
85  in  Fig.  610,  there  will  be  no  cutting  at  all  on  the  buccal  side,  but  a 

Fig.   609 

Fig.  610 


great  deal  on  the  lingual,  the  most  of  which  can  be  done  in  one  cut  with 
a  thin  disk. 

It  is  far  better  to  trim  too  much  than  too  little.  If  a  tooth  is  cut  away 
more  than  enough  to  remove  the  contour,  the  band  can  rest  on  the  ledge 
or  shoulder  and  the  cement  may  be  entirely  removed,  so  that  there  will 
be  no  irritation,  but  if  enough  has  not  been  taken  away,  w^hen  the  crown 
is  in  place,  the  band  will  cut  into  the  gum  and  the  cement  presents  a 


680  ARTIFICIAL  CROWNS. 

rou^li,  jagfjed  surface  to  tlie  soft  tissues,  causing  irritation  and  inflam- 
mation which  will  eventually  result  in  the  loss  of  the  tooth. 

The  bicuspids  are  trimmed  in  the  same  manner  as  the  molars,  but 
in  most  cases  a  strai<i;ht  or  Hat  disk  may  be  used  on  the  mesial  and  dis- 
tal sides.  The  point  of  difficulty  here  as  in  the  molars,  is  the  mesio- 
linj^ual  corner  and  this  will  have  to  be  trimmed  largely  with  the  scaler. 

At  the  masticating  surface  of  the  teeth  enough  tooth  structure  should 
be  ground  away  to  permit  the  placing  of  a  strong  thick  cusp,  especially 
where  it  is  to  serve  as  a  support  for  a  l)ridge.  This  can  best  be  done 
with  a  very  coarse  grit  sqmire-edged  wheel. 

The  shape  of  the  upper  is  very  different  from  that  of  the  lower  molars. 
Observed  from  the  masticating  surface,  they  are  somewhat  diamond- 
shaped  with  the  corners  rounded,  the  greatest  diameter  being  from  the 
anterior  buccal  to  the  posterior  palatal  corner.  (Fig.  611.)  This  is 
generally  the  shape  of  the  third  molars,  but  these  teeth  are  subject  to 
more  frequent  variations  in  form  than  the  others  of  the  upper  series. 

The  typical  form  of  the  upper  molars,  after  being  prepared,  is  not  at  all 
like  that  of  the  lowers.  It  is  somewhat  triangular  in  shape,  with  the  long 
dimension  on  the  mesial  side.  (Fig.  612.)  It  is  broader  at  the 
buccal  side  than  at  the  palatal,  because  there  are  two  buccal  roots  and 
but  one  palatal.  This  shape  may  vary  at  times  and  the  palatal  be  as 
large  or  even  larger  than  the  two  buccal  roots,  but  this  is  an  abnormal 
condition  and  will  be  readily  discovered  by  the  use  of  the  explorer. 

It  infrequently  happens  that  the  first  or  second  molars  will  have  but 
two  roots  and  when  this  is  the  case,  they  will  both  be  of  about  the  same 
size.  Very  rarely  they  may  have  but  one  root.  The  third  molars  are 
more  uncertain,  as  there  may  sometimes  be  but  one  at  other  times  sev- 
eral roots. 

The  trimming  of  these  teeth  is  much  easier  than  that  of  the  lower 
molars.  The  bulk  of  the  cutting  will  be  on  the  mesial  and  distal  sur- 
faces, the  greater  part  of  which  can  be  taken  away  with  one  cut  of  the 
disk  already  described.     For  the  buccal  and  palatal  surfaces  and  for 

Fig.  611  Fir,.  612  Fig.  613 


0 


the  corners,  the  cup-shaped  disks  and  inverted  cones  are  indicated. 
The  coarse  emery  cloth  disks  will  be  found  almost  invaluable  in  round- 
ing the  corners,  especially  the  posterior  buccal  and  palatal. 

The  bicuspids  are  trimmed  in  the  same  manner  as  the  molars. 
These  teeth  after  being  prepared  are  somewhat  egg-shaped,  in  cross 
section,  being  long  and  narrow  from  buccal  to  palatal  side,  broader  at 
the  buccal  and  having  slight  depressions  on  the  mesial  and  distal  sides. 
(Fig.  613.)  This  description  applies  chiefly  to  the  second  bicuspid,  as 
it  is  seldom  that  a  full  gold  crown,  on  account  of  its  conspicuousness, 
should  be  placed  farther  forward  in  the  mouth  than  that  tooth. 


MECHANICAL   PREPARATION  OF  TKETII   AM)   ROOTS.        681 

We  now  come  to  the  eight  anterior  teeth.  All  crowns  for  these 
teeth  shonld  be  of  porcelain  or  porcelain  faced.  The  method  of  their 
preparation  to  receive  a  band  is  somewhat  different  from  that  of  the 
other  teeth,  the  work  being  done  almost  entirely  with  enamel  cleavers 
and   scalers. 

The  typical  shape  of  the  roots  in  the  npper  jaw,  anterior  to  the  mo- 
lars, the  centrals  excepted,  after  being  prepared  for  the  reception  of  the 
band,  is  oval,  being  broadest  at  the  labial  side  and  narrow  at  the  palatal. 
This  must  of  necessity  be  the  case,  in  order  that  they  may  be  properly 
accomodated  in  the  arch.      (Fig.  614.) 

The  first  bicuspid  has  very  much  the  same  shape  as  the  second.  The 
shape  of  the  canines  and  laterals  is  almost  a  true  oval,  but  the  central 

Fig.  6U 


roots  while  of  the  same  general  ovoid  form,  are  more  distorted,  being 
somewhat  triangular  in  shape.  The  longest  side  of  the  triangle  is  on 
the  mesial  and  the  shortest  on  the  distal  side  of  the  root.  The  labial 
side  is  somewhat  flattened  and  generally  inclines  outward  toward  the 
median  line. 


Fig.  615 


Fig.  61(3 


^ 


Fig.  617 


^ 


In  preparing  these  teeth,  they  should  be  left  about  one-sixteenth  of 
an  inch  above  the  gum  line  until  after  the  root  has  been  trimmed  and 
the  band  has  been  fitted.  It  will  be  found  that  the  greatest  sectional 
area  of  the  root  of  these  teeth  is  at  the  point  of  junction  of  the  enamel 


682 


ARTIFICIAL  CROWNS. 


with  the  dentine.  (Fig.  615.)  The  enamel  must  be  entirely  removed, 
and  if  this  is  properly  done,  unless  there  has  been  a  recession  of  the 
gum,  the  root  will  be  of  the  proper  shape  for  the  reception  of  the  band 


Fig.  618 


Fig.  619 


s 


(Fig.  616),  which  should  take  the  place  of  the  enamel  and  fit  the  root 

tightly. 

For  removing  enamel,  the  enamel  cleavers  (Fig.  619),  and  scalers 


SHAPING   FACE  OF  ROOTS  AND  ENLARGING  CANALS.       683 

are  best  adapted.  On  the  mesial  and  distal  sides  the  thin  disks  may 
often  be  used  to  advantage.  For  the  labial  and  palatal  sides,  the 
No.  3  (S.  S.  W.)  scalers  are  the  best  (Fig.  618),  as  the  curve  of  the 
instrument  adaptsjlseif- nicely  to  the  root.  These  instruments  should 
ha\'e  short  heafy  handles  so  as  to  afford  a  sure  grip  for  the  hand,  and 
should  be  held  in  such  a  guarded  and  protected  manner  that  there 
will  be  no  chance^jof" the  instrument  slipping  and  injuring  the  soft 
tissues.  For  the  approximal  sides,  where  the  teeth  are  very  close 
together,  the  No.  7  (S.  S.  W.)  scaler  (Fig.  620)  will  be  very  useful. 
xA.t  the  basilar  ridge,  where  the  enamel  is  very  thick,  the  enamel 
cleavers  can  be  used  to  start  it,  afterward  finishing  with  a  No.  3 
scaler.  Where  the  gum  has  receded  beyond  the  edge  of  the  enamel, 
the  root  is  trimmed  in  the  same  manner,  the  sides  being  made  parallel 
or  slightly  convergent. 

Fig.  620 


The  root  of  the  lower  anterior  teeth  are  the  same  general  shape  as 
those  of  the  upper,  with  the  difference  that  the  bicuspids  are  nar- 
rower bucco-lingually  and  the  incissors  are  flattened  mesio-distally. 
These  roots  are  trimmed  with  scalers  in  the  same  manner  as  the 
upper  teeth. 

SHAPING  THE  FACE  OF  THE  ROOTS  AND  ENLARGING  THE  CANALS. 


The  further  preparation  of  a  root  in  the  anterior  part  of  the  mouth, 
after  the  enamel  has  been  removed,  varies  according  to  the  style  of 
crown  which  is  to  be  used.  In  any  case  where  the  root  is  to  be  banded, 
it  should  be  left  standing  about  one-sixteenth  of  an  inch  above  the  mar- 
gin of  the  gum  until  after  the  band  has  been  fitted.  For  taking  the 
measurement  of  the  root.  Kirk's  dentimeter  is  the  most  suitable  instru- 
ment. The  wire  is  placed  over  the  end  of  the  root  and  forced  as  far 
under  the  gum  as  is  possible  and  twisted  until  it  hugs  the  root  tightly. 
It  is  then  removed,  the  loop  cut,  the  wire  straightened  out  and  the  band 
cut  to  the  measurement  and  united  either  by  sweating  or  soldering.  It 
should  be  festooned  to  follow  the  gum  line  perfectly,  so  that  it  will  go 
an  equal  distance  below  the  margin  all  around.  After  the  band  has 
been  fitted,  it  is  removed  and  the  root  cut  to  its  proper  length.  It 
should  be  cut  at  least  one  thirty-second  of  an  inch  and  in  many  cases, 


684  ARTIFICIAL  CROWNS. 

nearly  or  quite  oiie-sixtceiitli  of  an  inch  below  the  jijvnii  line  on  the  la- 
bial or  buccal  side,  so  that  when  the  crown  is  })laced  on  the  root,  the  band 
will  be  completely  hidden.  (Fig.  021. )  Where  a  Richmond  crown  is 
to  be  used,  the  root  is  left  standinii  out  from  the  gum  on  the  palatal  or  lin- 
gual side  as  in  Fig.  ()21.  If  porcelain  is  to  be  used,  it  is  necessary  to 
have  as  great  an  amount  of  body  as  possible  to  give  strength  to  the 
crown,  this  being  of  necessity  a  very  fragile  material.  In  this  case  the 
root  should  be  cut  so  as  to  follow  the  line  of  the  septum  of  the  aKeolar 
process,  leaving  it  higher  in  the  centre  and  low  both  labially  and  lin- 
gually  as  in  Fig.  022. 

In  opening  up  the  root  for  the  pin,  if  it  is  enlarged  on  a  line  with  the 
canal,  the  pin  will  in  most  cases  come  wholly  or  partially  under  the 
facing  (Fig.  623),  necessitating  the  cutting  of  the  facing  to  accommodate 
it,  or  if  the  facing  is  to  set  close  to  the  floor,  which  is  desirable  in  the  six 
anterior  teeth,  the  cutting  away  of  the  end  of  the  pin,  so  that  the  only 
attachment  it  will  have  to  the  crown  will  l)e  to  the  thin  floor  of  the  cap, 
as  in  Fig.  624.  This  applies  more  particularly  to  Richmond  crowns 
on  the  six  anterior  roots,  either  single  or  those  to  be  used  as  abutment 
pieces  for  bridges.  The  better  way  to  do  is,  after  the  canal  has  been 
enlarged  in  a  direct  line,  to  incline  the  reamer  towarfl  the  palatal  side  of 


Fig.  621         Fig.  622      Fig.  623   Fig.  624    Fig.  625   Fu;.  626   Fig.  627 


^ 


the  root,  thus  sloping  the  canal  in  that  direction.  Now  by  bending 
the  pin  slightly,  there  will  be  ample  room  in  front  of  it  for  the  facing, 
the  pin  coming  up  behind  it  as  in  Fig.  625. 

For  porcelain  crowns,  the  root  should  be  enlarged  only  on  a  line  with 
the  canal,  especially  in  the  upper  jaw  where  the  strain  is  all  outward, 
and  the  facing  grooved  to  receive  the  pin,  so  as  to  have  as  great  an 
amount  of  porcelain  on  the  palatal  side  of  the  crown  as  possible,  to  give  the 
needed  strength.  (Fig.  626,  627)  Iii  the  lower  jaw  where  the  .strain 
is  inward,  the  pin  may  be  set  farther  in  toward  the  lingual  side  of  the 
root. 

REQUISITES  OF  A  CROWN. 

Artificial  crowns  should,  as  nearly  as  possible,  restore  tlie  appearance 
and  function  of  the  natural  teeth.  Moreover,  by  their  presence  they 
should  afford  no  more  opportunity  for  the  action  of  disease-producing 
agencies  than  wdien  a  natural  crown  is  upon  a  pulpless  root.  This  rule 
is  impossible  of  exact  fulfillment,  but  it  is  possible  that  by  a  correct 
artificial  crown,  properly  placed  upon  a  healthy  root,  the  possibilities 
of  disease  processes  arising  may  be  reduced  to  a  minimum  and  by  an 


POST  AND   PLATE  CROWNS.  685 

impr()})LTly  made  or  placod  crown  the  probabilities  of  subsequent  dis- 
ease are  increased. 

All  crowns  must  rest  firmly  upon  the  face  of  the  root  upon  which 
they  are  placed.  The  contact  must  be  at  all  points  of  the  edge  of  a 
crown  with  the  tooth  surface.  If  of  porcelain,  it  must  correspond  in 
shape,  size,  shade,  and  position  with  its  fellows,  and  must  suljserve  the 
purposes  of  a  crown  in  mastication. 

There  should  be  at  no  part  any  projection  which  can  form  part  of  a 
pocket,  nor  any  point  which  can  act  as  an  irritant  to  vital  tissue.  The 
line  of  junction  l)etween  tooth  and  crown  should  be  clean  and  clear,  so 
that  neither  the  surface  of  the  root  projects  beyond  the  edge  of .  the 
crown  nor  the  edge  of  the  crown  beyond  that  of  the  root. 

If  a  barrel  or  collar  crown,  the  gingival  edge  of  the  collar  or  barrel 
must  be  in  close  contact  with  the  root  surface.  It  should  extend  far 
enough  beneath  the  margin  of  the  gum  to  grasp  the  root  firmly,  but 
should  not  extend  to  the  alveolar  border.  A  limited  portion  of  perice- 
mentum is  destroyed  in  trimming  a  root,  and  the  collar  should  not  ex- 
tend beyond  this  point,  as  the  collar  represents  or  replaces  the  upper 
border  of  enamel,  it  should  not  extend  much  beyond  the  depth  of  the 
enamel  line  unless  the  gum  should  have  receded  from  about  the  tooth. 

Porcelain  crowns  should  have  the  porcelain  protected  against  frac- 
ture, either  by  the  inherent  strength  of  all  porcelain  crowns  themselves, 
their  bulk  supplying  the  strength  required,  or,  if  a  porcelain  facing,  the 
facing  should  be  protected  by  a  metallic  backing  against  the  force  or 
shocks  of  mastication. 

For  posterior  teeth  the  details  as  to  correspondence  of  size  and  con- 
tour are  equally  important,  and  in  addition  their  articulating  surfaces 
should  have  such  an  arrangement  of  cusps  and  sulci  that  the  normal 
masticating  surface  is  restored. 

TYPE  SELECTED. 

As  a  general  rule,  no  root  anterior  to  the  second  bicuspid  should  be 
crowned  with  an  all-gold  crown.  None  of  the  incisors  or  canines 
should  show  any  but  a  porcelain  surface.  Healthy  roots  which  have 
not  been  invaded  by  caries,  if  of  good^ize  and  structure,  as  a  rule,  may 
be  fitly  crowned  with  some  form  of  the  pin  crown. 

Logan  crowns  are  adapted  when  the  root  is  of  good  structure  and 
when  form  and  color  corresponding  exactly  to  the  adjoining  tooth  can 
be  had,  and  when  the  bite  is  not  too  close  to  cause  weakening  of  the 
porcelain  by  the  necessary  grinding,  and  where  the  correct  cervical 
surface  outline  can  be  had. 

THE   POST    AND   PLATE   CROWNS. 

These  are  crowns  which  have  posts  fitting  the  enlarged  pulp-canal 
for  support.  The  proper  size  and  shape  of  this  post  are  about  those 
used  in  the  familiar  Logan  crown. 

A  root  which  has  lost  no  substance,  or  no  more  of  the  periphery  of 


686  ARTIFICIAL  CROWNS. 

its  pulp-canal  than  will  receive  a  post  of  this  size,  is  usually  a  fit  root 
for  the  application  of  a  post  crown.  Should  there  be  a  loss  of  sub- 
stance in  excess  of  this  amount,  a  supportin<^  band  is  advisable. 

The  size  of  the  post  may  also  be  had  in  a  flattened  wire  of  14  B.  &c 
S.  gauge  and  somewhat  tapered  toward  its  extremity.  The  flattening 
increases  the  resistance  in  the  long  diameter,  which  occupies  the  antero- 
posterior line  of  the  pulp-chamber,  the  line  of  greatest  strain.  Round 
and  square  posts  are  needlessly  strong  for  one  diameter,  insufficiently 
so  in  the  other.  When  the  pin  is  double,  as  in  bicuspids  and  molars, 
round  or  square  pins  may  be  employed. 

The  old  type  of  post,  the  wood  pivot,  has  been  so  entirely  suoer- 
ceded  that  it  scarcely  needs  description.  These  crowns  were  anchored 
by  means  of  round  hickory  sticks,  which  were  compressed  immediately 
before  using.  A  suitable  crown  selected  was  ground  to  the  root  face, 
the  compressed  wood  set  in  its  base,  and  then  the  post  was  thrust  into 
the  enlarged  pulp-canal.  Roots  have  been  split,  frequently,  through 
the  swelling  of  the  compressed  wood. 

Fig.  628  Fig.  629  Fig.  030 


A  form  of  made-up  post  crowns  commonly  employed  is  selected  as 
the  typical  form;  it  is  the  pin  and  plate  crown.  A  detailed  description 
of  this  will  serve  to  illustrate  many  of  the  principles  governing  the 
making  of  all  crowns. 

The  method  of  making  is  as  follows:  an  incisor  or  canine  root  which 
is  in  a  perfectly  healthy  state  is  thoroughly  sterilized,  and  the  apical 
foramen  hermetically  sealed  by  some  unchangeable  material  which  has 
been  coated  or  saturated  with  a  strong  antiseptic;  usually  a  gutta- 
percha point  is  used  for  this  purpose,  one  which  has  been  soaked  in  one 
of  the  antiseptic  oils. 

The  pulp-canal  is  enlarged  for  about  two-thirds  its  length,  in  such 
shape  as  to  receive  a  flattened  pin  of  iridio-platinum  wire  of  No.  14 
B.  &  S.  gauge,  which  is  to  fit  the  enlarged  canal  easily  enough  to  permit 
ready  removal. 

The  face  of  the  root  is  shaped  to  follow  the  outline  of  the  gum  margin, 
and  to  have  its  surface  about  a  line  below  this  margin  (Fig.  629.)  At 
its  anterior  aspect  the  cutting  should  be  a  trifle  deeper  than  at  the 
other  parts,  to  ensure  perfect  hiding  of  the  joint.  The  operator  may 
now,  if  he  prefers,  take  an  impression  of  the  face  of  the  root,  and  fit  the 
root -plate  on  a  model  prepared  from  it.     An  effective  method  is  as  fol- 


POST  AND     PLATE  CROWNS. 


687 


lows:  after  shaping  the  post-canal  and  face  of  the  root  and  fitting  the 
post,  Melotte's  moldine  is  placed  around  the  pin,  covered  by  damp 
tissue-paper,  and  inserted  in  the  root;  an  impression  in  moldine  is  then 
taken;  after  removing  from  the  mouth  the  post  is  witluh-awn  and  placed 
in  position  in  the  impression,  and  a  die  of  fusible  metal  made.  Should 
the  paper  and  moldine  be  scraped  from  the  post  in  removing  it  from  the 
canal,  it  is  to  be  again  covered  by  moldine  enclosed  in  the  paper  before 
placing  it  in  the  impression. 

The  thin  layer  of  moldine  covering  the  post  permits  its  withdrawal 
from  the  die.  A  small  piece  of  soft  platinum  plate  No.  31,  or  of  24-carat 
gold  plate  No.  30,  is  well  annealed  and  placed  upon  the  root  face  repre- 
sented on  the  die,  and  pressed  into  rough  adaptation  (Fig.  628) :  a  piece 
of  erasing  rubber  answers  well  as  an  elastic  counter-die  for  this  purpose. 
A  buckshot  or  a  small  piece  of  soft  lead  is  placed  over  the  root  face  on 
the  die,  and  struck  with  a  hammer  until  it  is  fit  to  serve  as  a  counter-die. 

The  small  plate,  again  annealed,  is  placed  between  die  and  counter- 
die  and  swaged  with  a  light  hammer.  A  hole  is  made  in  the  plate  to  un- 
cover the  root  opening,  small  enough  to  require  force  in  pushing  the 
post  through  it,  so  that  the  post,  when  in  position,  is  closely  embraced 


Fig.  631 


Fig.  632         Fig.  633 


Fig.   634 


on  all  sides.  The  post  is  then  withdrawn,  the  plate  coming  with  it; 
borax  is  applied  at  the  hne  of  junction,  and  if  the  plate  is  platinum  it  is 
soldered  with  a  small  piece  of  24-carat  gold,  or,  if  the  plate  be  of  gold, 
with  a  minute  piece  of  22-carat  solder.  The  plate  is  then  trimmed  to 
follow  the  root  outHne;  at  its  labial  aspect  it  is  filed  to  a  thin  edge  (Fig. 

The  post  and  plate  are  placed  in  position  on  the  natural  root,  and 
with  an  orange-wood  stick  and  a  light  mallet  tapped  at  all  points  until 
the  adaptation  is  perfect. 

A  bite  of  wax  which  includes  the  adjoining  teeth  is  now  taken,  re- 
moved, and  chilled. 

Next  a  plaster  impression  is  secured,  in  which  are  withdrawn  the 
post  and  plate;  if  not  withdrawn  in  the  impression,  a  depression  is  seen, 
in  which  the  top  of  the  pin  is  inserted. 

A  shade  tooth  is  selected  at  this  time.  The  impression  is  double 
varnished  with  thin  shellac  and  thin  sandarac,  allowing  each  varnish  to 
dry  well.  Pins  are  placed  in  the  impressions  of  the  teeth  adjoining  the 
root  to  be  crowned,  and  poured  carefully  with  rather  thin  plaster,  to  be 


688  ARTIFICIAL  CROWNS. 

sure  the  impressions  of  the  tips  of  the  teeth  nre  perfectly  filled.  Let 
this  set  well  before  separating  the  east  from  the  impression;  place  the 
wax-bite  in  position  on  the  model,  and  make  an  articulation  on  a  crown 
articulator. 

Varnish  with  thin  shellac  the  teeth  of  the  casts. 

Saw  off  the  ])rotruding  end  of  the  post  to  within  one-sixteenth  of  an 
inch  of  the  ])late;  the  anterior  edge  of  the  post  may  be  beveled  even 
with  the  plate;  removing  more  than  this  weakens  the  post  attachment 
to  the  plate. 

A  plain  plate,  straight  pin  tooth,  having  a  shape,  size,  and  color 
corresponding  with  the  adjoining  tooth,  is  then  selected.  Straight  pin 
teeth  are  stronger  than  those  with  cross  pins;  but  the  lower  pin  must  be 
in  such  situation  that  it  will  not  be  ground  out  in  the  fitting.  Grind 
the  tooth  with  fine  grit  corundum  wheels  until  the  cervical  portion  fits 
perfectly  the  outer  edge  of  the  plate  and  has  the  same  contour:  the  cut- 
ting edge  should  be  precisely  on  a  line  with  its  fellow  and  restore  the 
general  curve  of  the  incisors,  repairing  the  break  of  the  arch  line. 

Fig.  035 


Bevel  the  palatal  aspect  from  about  one-eighth  of  an  inch  beneath  to 
the  cutting  edge,  and  bevel  the  porcelain  beneath  the  lower  pin  to  ex- 
pose the  head  of  the  post  (Fig.  631.)  Make  a  small  plaster  wall  to  hold 
the  tooth  while  fitting  the  backing  stay.  Should  the  tooth  be  a  little 
blue  in  color,  use  24-carat  plate  for  backing;  if  a  trifle  yellow,  use 
platinum  plate.     (Fig.  632.) 

A  crown  which  consists  merely  of  post  and  plate  without  collar  or 
band  offers  no  reinforcement  to  the  root  to  which  it  is  attached,  and  frac- 
ture of  a  root  thus  mounted  is  very  liable  to  occur,  particularly  in  the 
lateral  incisor  teeth,  in  consequence  of  the  leverage  thnnvn  upon  them 
during  the  incision  of  resistant  articles  of  food  (Fig.  G35.)  Accidents 
of  this  nature  are  not,  however,  always  irremediable,  and  roots  thus 
broken  may  often  be  made  quite  strong  and  useful  again  by  forcing  a 
tightly-fitting  narrow  band  of  gold  around  the  root  at  the  gingival  mar- 
gin (Fig.  635.) 

Usually  when  such  a  fracture  occurs  the  artificial  crown  will  soon  drop 
off,  and  unless  the  band  or  collar  is  applied  within  a  few  days  of  the 
accident,  the  fractured  parts  of  the  root  will  be  separated  by  ingrowing 
gum  tissuse,  when  it  will  be  difficult,  if  not  impossible,  to  bring  them 
into  juxtaposition,  but  when  promptly  done  the  crown  may  be  reset 
with  oxy-phosphate  cement  with  satisfactory  results. 


COLLAR  CROWNS. 


689 


COLLAR  CROWNS. 


Fig.  6.36 


The  second  class  of  crowns  are  those  in  which  retention  is  by  means 
of  encirchno;  collars  or  bands.     As  the  band  is  the  distinctive 
feature  of  this  class,  it  will  be  first  described. 

The  first  requisite  of  this  band  is  that  it  shall  fit  absolutely, 
not  approximarely.  Faults  in  this  direction  are  the  most 
common  and  those  to  be  most  guarded  against.  The  second 
requisite  is  that  these  bands  shall  not  be  irritating  to  the 
vital  parts,  and  yet  shall  offer  a  perfect  protection  against 
the  ingress  of  pathogenic  organisms  or  their  products  to  the 
parts  we  design  to  protect.  This  implies  that  the  band  shall 
not  impinge  on  the  pericementum,  nor  must  it  have  any 
roughened  edge  or  surface  to  irritate  the  overlying  gum.  It 
should  extend  to  such  depth  beneath  the  gum  margin  that 
the  o-ingival  margin  shall  form  a  barrier  not  the  vrall  of  a 

•        •  •  n 

pocket.  The  band  should  grasp,  but  not  irritate;  a  trme 
over  one-sixteenth  of  an  inch  in  depth  will  be  sufficient  in 
the  majority  of  cases. 

A  method  of  fitting  tlie  collars  is  as  follows:  the  peri- 
meter of  the  root  is  taken  by  means  of  annealed  brass  wire 
of  No.  33  gauge.  The  ends  of  the  wire  are  passed  through 
the  end  openings  of  a  dentimeter,  one  end  being  caught  fast 
upon  the  side  pin  of  the  instrument,  and  by  drawing  upon 
the  loose  end  of  the  nose  of  the  dentimeter,  is  drawn  to  with- 
in an  eighth  of  an  inch  of  the  outer  face  of  the  root,  when 
the  instrument  is  turned,  twisting  the  "wire  and  drawing  it 
closely  about  the  neck  of  the  teeth.  The  opposite  edge  of 
the  wire  loop  is  held  down  by  means  of  an  instrument  to  pre- 
vent it  slipping  off  the  root. 

The  loop  is  removed  (Fig.  636)  and  di^^ded  at  a  point  op- 
posite the  twist,  and  straightened.  The  line  of  greatest  dis- 
ance  between  the  gum  line  of  the  root  to  be  crowned  and  the 
antagonizing  tooth  is  measured,  and  a  rectangle  of  plate  of 
that  -VNadth  and  the  length  of  the  straightened  wire  is  cut. 
In  the  making  of  a  gold  band  or  collar  for  a  tooth  or  root, 
it  is  better  to  make  a  lap-joint  than  an  abutted  joint,  as  the 
lap-joint  is  stronger  and  less  liable  to  separate  in  subsequent 
solderings.  ^Yhe^e  no  solder  is  used  and  the  sweating  pro- 
cess is  employed,  the  ends  of  the  band  may  be  lapped  or 
simply  abutted.  This  is  the  strongest  union  that  can  be 
made  and  the  parts  cannot  be  separated  by  any  amount  of 
heat.  It  is  well  to  have  the  point  of  union  come  on  one  of 
the  approximal  sides  of  the  tooth. 

If  the  operator  prefer  he  may  employ  a  seamless  gold 
collar,  procured  from  the  manufacturer,  and  form  this  upon 
a  mandrel.    Making  a  soldered  cylinder  for  each  case  is,  however,  a 

44 


Kirk's  den- 
timeter. 


090  ARTIFICIAL   CROWNS. 

more  precise  metliod;  moreover,  it  permits  of  making  tlie  cireiimferenee 
of  one  edfje  of  the  collar  jjreater  than  that  of  the  other  when  this  differ- 
ence in  the  sizes  is  demanded. 

'I'he  exact  neck  forms  may  be  given  in  the  following  manner:  lay 
the  wire  loop  as  it  comes  from  the  tooth  upon  a  smooth  flat  lead  surface, 
and  place  over  it  an  old  tool-handle,  sawed  square  and  given  a  smooth 
surface.  Strike  the  wood  a  hard  blow,  driving  the  wire  into  the  lead 
and  wood,  leaving  both  lead  and  wood  marked  by  the  outline  form  of 
the  wire.  The  wire  is  straightened,  the  gold  measured,  and  the  cylin- 
der made  as  described.  It  is  then  bent  to  fit  the  indentation  made  by 
the  wire  in  the  wood,  and  next  further  adapted  to  the  groove  in  the  lead. 
Tt  is  then  transferred  to  the  root  in  the  mouth,  the  outline  of  the  gum 
margin  marked  on  its  surface,  and  the  collar  trimmed  to  this  line. 

It  is  set  upon  the  root  until  one  portion  of  it  touches  the  gum,  when 
the  outline  to  which  the  edge  of  the  collar  must  be  cut  is  noted,  so  that 
it  shall  be  at  a  uniform  depth  below  the  gum  line.  The  collar  is  cut  to 
this  line,  transferred  to  the  root  or  tooth,  and  pushed  into  position. 

Subsequent  manipulations  depend  upon  the  class  of  tooth  to  be  re- 
placed, for  there  are  many  modifications  of  the  subsequent  operations 
depending  upon  whether  the  tooth  has  or  has  not  a  vital  pulp,  and 
whether  the  root  is  that  of  an  incisor,  canine,  bicuspid  or  molar. 

As  the  molar  is  the  commonest  of  full  gold  or  barrel  crowns,  it  w^ill  be 
described  first.  Many  time-saving  methods  are  recommended  and 
applied  in  the  making  of  these  crowns,  but  in  most  of  them  time-saving 
is  at  the  expense  of  aesthetic  results. 

FULL  GOLD  CROWNS. 

In  the  consideration  of  full  gold  crow^ns,  as  the  built  up,  solid-cusp 
crown  is  unquestionably  better  than  any  other  and  as  it  is  probably 
most  quickly  and  easily  made,  its  construction  will  be  described.  The 
measurement  of  the  root  is  taken;  the  band  is  made  of  No.  30  coin  gold 
and  fitted  to  the  stump,  following  the  gum  line  carefully  and  extending 
about  one-sixteenth  of  an  inch  below  it.  It  is  then  cut  down  a  little 
short  of  the  occlusion,  replaced  on  the  stump  and  the  impression  and 
bite  taken.  The  impression  should  always  be  taken  in  plaster  of  a  very 
fine  grade.  Modelling  composition  or  wax  should  never  be  used. 
If  there  are  dovetailed  spaces  or  under-cuts  to  be  secured,  modelling 
composition  will  not  give  an  accurate  impression,  but  whatever  the 
position  or  condition  of  the  teeth  may  be,  a  cast  made  from  a  carefully 
taken  plaster  impression  will  be  an  exact  reproduction  of  the  parts. 

The  bite  should  also  be  taken  in  plaster,  and  this  may  be  done  sim- 
ultaneously with  the  taking  of  the  impression.  The  advantage  of 
taking  the  bite  and  impression  at  the  same  time  in  plaster  is  the  abso- 
lute accuracy  of  the  relation  of  the  upper  and  lower  teeth  which  is  thus 
secured.     Where  the  bite  is  taken  in  this  way,  it  is  possible  to  make  and 


FULL   (I OLD   CROWNS.  601 

articulate  a  crown  or  a  l)ri(Ige  so  perfectly  that  when  it  comes  from  the 
cast,  it  is  finished  and  will  not  have  to  be  touched  to  correct  the  articu- 
lation when  it  is  j)laced  in  the  mouth.  When  a  tray  is  used  for  the 
plaster  i]n{)ression  and  the  bite  is  separately  taken  in  wax,  the  occlusion 
of  the  piece  will  invariably  have  to  be  readjusted  when  it  is  placed  in 
the  mouth.  It  is  then  sent  back  to  the  laboratory  for  a  second  finishing 
and  polishing,  or  if  it  is  finished  in  the  mouth,  the  polishing  can  never 
be  properly  done.  The  cusps  and  fissures,  which  are  necessary  for  per- 
fect mastication,  are  partly  or  wholly  obliterated  and  the  usefulness  and 
beauty  of  the  piece  is  destroyed  or  at  least  impaired. 

As  the  impression  and  bite  are  conjointly  taken  in  a  similar  manner 
for  a  single  crown  or  for  a  bridge,  the  description  of  one  will  answer  for 
both.  Suppose  it  to  be  a  bridge  case;  the  abutment  caps  having  been 
made,  they  are  placed  in  position  on  the  teeth  or  roots  and  the  patient 
instructed  in  opening  and  closing  the  mouth  so  that  the  correct  occlu- 
sion may  be  secured.  Every  one  knows  how  difficult  and  at  times 
almost  impossible  it  is  to  get  patients  to  close  the  mouth  properly. 
The  mandible  is  protruded  or  thrown  to  one  side  or  the  other  as  they 
l)ite  into  the  plaster  or  wax.  If  while  the  mouth  is  open,  the  patient 
is  told  to  place  the  tip  of  the  tongue  far  back  on  the  soft  palate,  and  to 
keep  it  there  while  the  mouth  is  being  closed,  it  will  be  difficult  for  the 
patient  to  give  the  wrong  bite,  as  when  the  jaw  is  thrust  forward  or  to 
one  side,  the  tongue  must  move  with  it.  In  any  but  large  cases,  a 
little  salt  or  potassium  sulphate  should  be  used  to  hasten  the  setting  of 
the  plaster,  but  in  very  large  cases,  nothing  should  be  used  for  this  pur- 
pose, as  the  plaster  is  likely  to  set  before  it  can  be  properly  distributed. 
The  plaster  should  be  thoroughly  mixed,  and  when  it  is  so  stiff  that 
it  will  not  fall  from  the  spatula  when  the  latter  is  inverted  or  turned  edge- 
wise, it  is  ready  for  the  mouth.  It  is  carried  in  on  the  spatula  and 
the  abutment  teeth  should  be  well  covered ;  a  few  of  the  adjoining  teeth 
are  included  in  the  impression  and  the  plaster  is  built  up  thickly  in  the 
space  intervening  between  the  abutments.  The  surfaces  of  the  oc- 
cluding teeth  in  the  opposite  jaw  are  also  covered,  and  the  patient  is  in- 
structed to  close  the  mouth,  to  bring  the  teeth  tightly  together,  and 
cautioned  not  to  move  the  jaws  until  the  plaster  is  well  set.  The  teeth 
which  are  not  included  in  the  impression  are  carefully  examined  to  see 
that  the  jaws  are  in  their  correct  occlusal  relation.  With  a  wet  spatula, 
the  plaster  may  be  smoothed  and  pressed  around  the  teeth  and  gums 
on  the  labial  and  buccal  sides. 

The  patient -is  requested  to  separate  the  jaws  slowly  and  carefully 
when  the  impression  is  hardened,  and  it  is  removed,  coming  away  gener- 
ally in  a  more  or  less  broKen  condition;  the  broken  parts  are  easily 
united  and  fastened  together  with  adhesive  wax.  The  abutment  caps 
are  then  removed,  if  they  have  not  come  away  with  the  plaster,  and 
placed  in  position  in  the  impression.  Their  inner  surfaces  are  to  be 
given  a  coating  of  melted  pink  wax,  enough  being  used  to  obliterate 
any  under  cuts.     The  impression  is  then  varnished  and  the  cast  run. 


692  ARTIFICIAL  CROWNS. 

In  extensive  cases  it  is  best  to  use  an  anatomical  articulator,  but  for 
most  small  bri(lg(\s  and  for  single  crowns  a  plaster  articulator  may  be 
used.  In  making  the  cast  from  a  bite  of  this  kind,  the  lower  half  of 
the  impression  is  run  first.  The  reason  for  this  is,  that  by  having  a 
regular  system  for  running  casts,  the  operator  always  knows  just  how 
to  separate  them  safely.  When  the  sides  of  the  casts  are  trimmed,  the 
grooves  in  their  posterior  extensions  (to  be  referred  to  presently),  will 
enable  him  to  distinguish  at  once  the  upper  from  the  lower  side  and 
to  know  just  how  to  cut  without  danger  of  injuring  the  cast.  The 
casts  should  be  well  trimmed  and  should  be  no  larger  than  is  necessary. 

Working  casts  should  always  be  made  of  the  harflest  plaster  obtain- 
able. Hard  plaster  is  always  coarse  and  can  be  distinguished  by  rub- 
bing a  small  amount  of  it  between  the  thumb  and  finger.  It  is  always 
slow  setting  and  nothing  should  be  used  to  hasten  this,  as  rapidity  of 
setting  is  gained  at  the  expense  of  hardness.  It  should  be  mixed 
with  cold  water,  and  if  stirred  at  all,  only  just  enough  to  secure  a  homo- 
genous mass.  Much  stirring  has  the  same  effect  as  the  use  of  salt  or 
warm  water,  making  the  plaster  set  more  quickly  but  reducing  its  hard- 
ness. 

For  a  separating  medium,  sandarac  varnish  gives  as  good  results  as 
any  thing  that  may  be  used.  It  is  first  colored  with  a  little  carmine, 
or  a  Uttle  of  the  crayon  of  an  indelible  or  of  a  copying  pencil  scraped 
into  the  varnish.  Only  a  little  of  the  crayon  is  needed  to  impart  a 
pinkish  or  purplish  tint.  The  impression  should  be  slighly  moist  for 
varnishing,  since  if  it  is  dry,  the  sandarac  will  soak  into  the  plaster  and 
will  not  give  a  glazed  surface;  while  if  it  is  too  wet,  the  varnish  will  not 
adhere  sufficiently  but  will  scale  off.  If  the  impression  has  dried  out, 
it  should  be  dipped  in  water  and  then  laid  on  blotting  or  bibulous  paper 
for  a  few  minutes  before  varnishing.  It  will  make  the  separation 
from  the  cast  easier  if  the  surface  of  the  impression  is  dusted  with  tal- 
cum powder,  the  excess  of  which  should  be  blown  out  with  a  chip  blow- 
er. Oil  should  not  be  used  as  a  separator,  as  it  has  a  tendency  to  make 
the  cast  soft.  A  soap  solution  makes  an  excellent  separating  medium. 
The  impression  is  coated  thoroughly  with  the  solution,  using  a  soft 
brush  to  apply  it,  after  which  it  is  well  rinsed  in  clear  water.  If  this 
is  not  done  and  any  of  the  suds  are  left  in  the  impression,  the  surface 
of  the  cast  will  be  covered  with  holes  and  bubbles. 

The  plaster  for  the  cast  should  be  mixed  a  little  stiffer  than  for  tak- 
ing impressions.  The  half  of  the  impression  which  is  to  be  poured 
first,  is  filled  with  water,  the  most  of  which  is  shaken  oui,  leaving  a 
little  in  the  bottom.  A  very  small  quantity  of  ])laster  is  now  placed  on 
the  edge  of  the  impression  and  worked  down  into  it  with  a  jolting  or 
jarring  motion,  adding  a  little  at  a  time  until  it  is  filled.  A  small 
camel's  hair  brush  may  be  used  to  work  the  plaster  in,  but  will  give  no 
better  results  than  the  method  described,  if  due  care  is  used  to  avoid 
the  confining  of  air. 

After  the  impression  has  been  filled,  the  remaining  plaster  is  scraped 


FULL   GOLD  CROWNS. 


693 


from  the  bowl  upon  a  glass  slab  and  the  filled  impression  inverted 
upon  this.  The  plaster  should  extend  an  inch  or  more  beyond  the  dis- 
tal side  or  end  of  the  impression  and  a  separating  plate  (Fig.  637) 


Fi(i.  037 


Fig.  638 


Fig.    639 


pressed  into  it,  the  ridge  side  down.  (Fig.  '638.)  This  is  allowed  to 
remain  for  a  few  minutes  until  the  plaster  has  set,  when  it  is  removed. 
The  cast  is  trimmed  and  the  surface  produced  by  contact  with  the 
separating  plate  is  varnished,  and  after  allowing  it  to  dry  for  a  few 
minutes,  the  upper  half  is  run  in  the  same  manner 
as  the  lower,  covering  the  varnished  extension  with 
plaster  and  pouring  the  surplus  on  the  slab,  the 
upper  half  being  pressed  into  it.  After  allowing  it 
to  harden  for  a  few  minutes,  it  is  removed  from  the 
slab  and  trimmed.  In  the  absence  of  the  separating 
plates,  the  plaster  may  be  smoothed  with  a  spatula, 
and  after  it  has  become  hard,  grooves  or  notches  may  be  cut  in  it  with 
a  knife,  after  which  it  is  varnished  as  before.  In  separating,  the  im- 
pression is  carefully  cut  away  from  the  sides,  until  the  purplish  tint 
from  the  varnish  shows  that  the  cast  is  near,  and  the  teeth  are  uncovered 
as  far  as  possible.  When  the  impression  is  nearly  all  cut  away,  the 
point  of  a  knife  is  introduced  between  the  articulating  surfaces  and  by 
a  little  careful  prying,  the  halves  are  separated,  after  which  the  remain- 
der of  the  impression  is  easily  removed.  The  casts  are  then  trimmed 
and  smoothed  and  if  they  are  rubbed  with  talcum  powder,  it  will 
give  them  a  beautiful  polished  surface. 

If  the  tooth  or  root  has  been  properly  prepared,  the  band  may  be 
made  and  the  crown  or  bridge  completed  without  the  band  having  been 
first  fitted  in  the  mouth,  the  whole  of  the  work  being  done  on  the  pre- 


694 


A  R riFICIA L   CRO WNS. 


Fig.  040 


parrd  cast.     In  prepariiiii;  the  cast  for  this  procedure,  it  is  first  drietl 
thoiouglily  and  then  trinniied,  cutting  down  on  a  Hne  with  the  sides  of 

ihe  tootli  to  nearly  one-sixteenth 
of  an  inch  below  and  parallel  to 
the  cervical  margin.  (Fig.  639.) 
After  the  trimming,  it  is  soaked 
with  thin  sandarac  varnish  and 
again  dried.  This  will  make 
the  cast  hard  enough  to  with- 
stand the  wear  incident  to  fitting 
the  bands.  The  sandarac  var- 
nish as  purchased  at  the  dental 
depots,  diluted  one-half  with  alco- 
hol, is  suitable  for  this  purpose. 
If  the  band  has  been  fitted  to 
the  tooth,  and  after  the  articula- 
ting cast  has  been  obtained,  it  is 
removed  by  grasping  it  with  a  pair 
of  slightly  heated  pliers,  which 
melts  the  wax  at  its  inner  surface: 
the  wax  is  burned  off  and  it  is 
cleansed  in  dilute  sulphuric  acid. 
The  contour  is  made  by  stretch- 
ing the  band  toward  the  occlusal 
portion.  This  may  be  done  on 
the  beak-iron  of  an  anvil  w4th  a 
small  hammer,  or  with  a  pair  of 
stretching  pliers  designed  especi- 
ally for  this  purpose.  (Fig.  640.) 
It  is  then  annealed  and  given 
the  desired  shape  with  the  fingers 
and  collar  phers.  The  band  is 
placed  on  the  cast  and  the  buccal 
and  lingual  sides  grasped  between 
the  thumb  and  finger  and  pressed 
in  until  they  are  on  a  line  with 
the  other  teeth.  The  plier'?  are 
then  used  to  make  the  buccal 
and  palatal  or  lingual  fissures 
and  to  remove  any  little  irregu- 
larities which  may  exist  in  the 
band.  It  is  now  cut  short  enough 
to  allow  the  placing  of  a  thick  solid  cusp  and  the  top  edge  filed  per- 
fectly fiat.  If  from  a  plate  or  buttons  a  suitable  cusp  can  be  selected,  a 
matrix  of  very  thin  pure  gold  is  made  from  it  by  swaging  into  a  Melotte's 
metal  die,  and  this  is  filled  with  coin  gold  and  the  under  surface  filed 
Hat  so  that  there  will  be  perfect  contact  between  its  periphery  and  the 


JACKET  CROWNS.  695 

band.  These  are  then  wired  together  with  iron  binding  wire,  the  wire 
being  twisted  at  the  under  side  of  the  band  as  in  Fig.  041,  and  a  little 
borax  or  soldering  fluid  placed  around  the  inside  at  the  pomt  of  contact 
with  the  cusp.  A  couple  of  pieces  of  solder  are  now  placed  on  the  in- 
side next  to  the  band  and  the  crown  held  over  the  flame  of  a  Bunsen 
burner  by  the  twdsted  wire  until  the  solder  has  flowed  all  around.  The 
wire  is  then  removed,  the  crown  cleansed  in  acid,  any  overhanging 
edges  of  the  cusp  ground  away,  and  the  crown  finished  and  polished. 

In  the  event  of  a  suitable  cusp  not  being  found,  the  top  of  the  band 
may  be  filled  with  soft  plaster  or  modelling  composition  and  the  oc- 
cluding teeth,  having  been  previously  covered  with  oil  or  talcum  pow= 
der,  pressed  into  it.     After  the  plaster  or  composition  has 
hardened,  the  cusp  is  carved  to  represent  as  far  as  possi-        Fig.  64i 
ble  a  typical  cusp  for  the  given  tooth,  and  a  die  of  fusible 
metal  made  and  solid  cusp  secured  as  already  described. 

A  much  better  way  of  making  these  crowns,  is  to  use 
no  solder  at  afl,  but  to  sweat  the  joints  throughout.  If 
solder  is  used,  it  is  sure  to  discolor  in  time  and  dark  lines 
will  indicate  the  several  joints.  The  sweating  of  the  band 
is  best  done  with  the  blowpipe.  The  band  is  placed  on  a  charcoal  block 
with  the  seam  to  be  united  uppermost,  covered  with  a  little  borax  or 
soldering  fluid.  The  flame  used  is  the  inner  blue  point  of  the  blowpipe- 
flame  and  should  be  from  an  inch  to  an  inch  and  a  quarter  in  length.  The 
whole  of  the  band  is  brought  to  a  very  bright  red  heat  and  the  point 
of  the  blue  flame  gently  passed  over  the  joint,  melting  the  gold  to- 
gether at  that  point  and  at  no  other.  This  makes  a  stronger  union  than 
can  be  made  with  any  solder.  The  higher  the  carat  of  the  solder 
used,  the  stronger  is  the  union  and  where  none  is  used,  the  band  will 
be  practically  seamless  and  as  strong,  or  stronger  at  that  point  than  at 
any  other.  The  band  is  then  festooned,  contoured,  and  filed  flat  as 
already  described.  The  cusp  is  made  and  wired  to  the  band  as  in  the 
soldered  crown.  It  is  then  fluxed  and  held  by  the  twisted  wire  with  a 
pair  of  light  pliers,  cusp  down  over  a  Bunsen  flame  well  toward  the  top, 
so  that  the  thick  cusp  will  be  heated  first  until  it  is  nearly  at  the  melting 
point.  The  crowm  is  then  lowered  a  little  in  the  flame  and  held  until  the 
gold  begins  to  melt  and  unite  the  band  with  the  cusp  after  which  it  is 
cleansed  in  acid  and  the  crown  finished  and  polished. 


JACKET   CROWNS. 

There  are  times  when  it  is  desirable  to  preserve  the  pulp  of  a  tooth 
anterior  to  the  molars  where  through  accident  or  decay  the  tooth  is  too 
far  broken  down  to  be  restored  with  inlays  or  fillings.  As  in  the  six  or 
eight  anterior  teeth  the  placing  of  a  gold  crown  is  out  of  the  question, 
it  becomes  necessary  to  make  a  shell  which  will  cover  the  stump,  and 
protect  the  pulp,  to  which  may  be  attached  a  porcelain  facing.     The 


69G  ARTIFICIAL  CROWNS. 

face  of  the  tooth  is  ground  away  as  much  as  possible  without  endanger- 
ing the  hfe  of  the  pulp,  cutting  well  under  the  gum  as  in  Fig.  642.  The 
sides  and  palatal  portions  of  the  tooth  have  their  enamel  removed,  so  that 
the  band  will  hug  the  root  tightl>-  under  the  gum.  (Fig.  ()43.)  The  baitd 
is  then  made  and  fitted  to  the  stump  and  cut  out  on  the  labial  side 
flush  with  the  tooth.  (Fig.  644.)  The  palatal  side  of  the  band  is  then 
pressed  in  close  to  the  stump  and  the  mesial  and  distal  sides  of  the 
band  spread  out  nearly  or  quite  to  the  width  of  the  facing  which  is  to 
be  usetl,  and  a  floor  of  coin  gold  sweated  or  soldered  to  it.  (Fig.  645.) 
A  thin  facing  is  then  ground  so  as  to  leave  a  little  space  between  it  and 

Fig.  642  Fig.  643  Fig.  644 


A 


the  cap,  touching  the  latter  only  at  the  tip.  (Fig.  646.)  The  facing  is 
now  backed  with  thin  platinum  or  crown  metal,  letting  it  extend  about 
one-sixteenth  of  an  inch  over  the  incisal  edge.  It  is  then  waxed  to  the 
cap,  invested  and  soldered,  flowing  the  solder  between  the  facing  and 
the  cap  and  if  necessary  over  the  palatal  portion  of  the  band.  (Fig.  647.) 
Another  way  of  making  this  crown  is  to  carry  the  band  to  the  full 
height  of  the  tooth,  to  contour  it,  and  cut  it  out  on  the  face  to  the  depth 
of  the  facing.  The  facing  is  then  ground  to  fit  the  edge  of  the  cap  so 
formed  and  a  backing  of  coin  gold  fitted  carefully  to  it.  This  is  then 
adjusted  to  the  cap,  waxed,  the  facing  removed  and  the  backing  sol- 
dered to  the  cap  with  22  carat  solder.     The  facing  is  then  put  in  place, 

Fig.  645  Fig.  646  Fig.  647 


the  pins  waxed  on  the  inside  of  the  cap,  and  the  crown  invested.  The 
crown  is  invested  face  down  and  covered  but  lightly,  leaving  the  opening 
fully  exposed  as  in  Fig.  648.  It  is  thoroughly  dried  out  and  flux  placed 
on  and  around  the  pins.  A  piece  of  18  or  20  carat  solder  is  then  placed 
over  the  pins,  the  whole  brought  to  a  bright-red  heat,  and  with  the  fine 
blue  point  of  the  blowpipe-flame  thrown  on  the  inside  the  solder  is 
melted,  uniting  the  facing  to  the  cap. 

In  the  making  of  a  porcelain  faced  crown  for  a  bicuspid  having  a 
vital  pulp,  the  tooth  is  prepared  in  the  same  way  as  in  the  anterior 
teeth,  cutting  it  well  out  on  the  buccal  side  and  grinding  away  the  inner 
cusp.  (Fig.  649.)  The  band  is  then  made  as  for  a  full  gold  crown, 
and  cut  even  with  the  cusp  at  the  top  and  enough  on  the  buccal  side  to 


JACKET  CROWNS.  697 

allow  for  the  facing.  (Fig.  650.)  The  facing  is  then  ground  to  fit  the 
edges  of  the  cap  (Fig.  651)  and  a  backing  of  coin  gold  fitted  to  it.  (Fig. 
652.)  The  backing  being  fitted  to  the  facing,  it  is  placed  in  position  on 
the  cap  and  waxed  and  soldered  with  22  carat  solder.  The  backing  is 
then  cut  off  e\-en  with  the  rest  of  the  band  and  filed  flat.  (Fig.  653.) 
The  tip  of  the  facing  is  then  ground  on  a  bevel  with  an  angle  of  about 
forty-fi\-e  degrees,  the  lower  edge  of  the  bevel  being  on  a  line  with  the 
top  of  the  cap.  (Fig.  654.)  A  cusp  is  then  selected,  the  under  surface 
filed  flat  and  the  buccal  side  beveled  to  meet  the  bevel  of  the  facing. 
(Fig.  655.)  The  cusp  is  then  wired  to  the  cap  and  soldered  with  22 
carat  solder,  the  facing  having  first  been  removed.     The  cap  is  then 

Fig.  649  Fig.  650  Fig.  651  Fig.  652 


cleansed  in  acid  and  the  facing  replaced  in  position  and  waxed.  It  is 
then  invested  and  soldered  from  the  inside  as  already  described. 
(Fig.  648.) 

Another  method  of  attaching  porcelain  facings  to  the  gold  barrel 
crown  is  by  first  making  the  entire  crown  of  gold,  the  barrel  and  articu- 
lating surface  being  completed.  The  external  wall  of  the  crown  has 
the  segment  made  visible  by  the  movements  of  the  lips  sawed  out,  and 
the  cut  edges  of  the  metal  beveled.  A  porcelain  facing  is  selected  of  a 
size  to  fit  the  space  with  the  minimum  grinding.  It  is  to  be  ground  in 
until  all  of  its  edges  fit  those  of  the  barrel.  A  stay  of  No.  34  pure 
gold  is  burnished  over  the  back  of  the  porcelain  tooth.     The  edge  of 

Fig.  653  Fig.  654  Fig.  655 


the  stay  should  be  accurately  adapted  to  the  barrel.  The  crown  ana 
facing  are  cemented  together  with  adhesive  wax,  covered  by  a  thin 
investment,  and  soldered  by  means  of  a  blowpipe-flame  directed  against 
the  portion  of  the  investment  covering  the  facing. 

The  buccal  and  articulating  faces  of  molars  and  bicuspids  may  be 
made  of  porcelain,  the  attachment  of  the  crown  to  the  root  being  secured 
by  means  of  a  gold  barrel.  The  barrel  is  made  as  for  an  all-gold 
crown.  A  wax-bite  and  impression  are  taken,  and  an  articulation 
mounted.  Before  cutting  away  the  buccal  wall  of  the  barrel  for  the 
reception  of  the  porcelain,  measure  by  means  of  a  ^dre  and  dentimeter 
the  circumference  of  the  upper  portion  of  the  barrel.  The  loop  made 
is  taken  to  the  depot,  and  a  saddle-back  or  a  plain  rubber  tooth  is 


Gds 


ARTll'ICIAL  CROWNS. 


Fig.  656 


selected,  the  eircumference  of  which  agrees  with  that  of  the  barrel  (the 
wire  loop).  The  tooth  should  have  but  little  thickness  of  porcelain 
above  the  pins  (Fig.  ()5());  the  S.  S.  \V.  cusp  crowns  are  designed  for 
this  special  use.  A  scratch  is  made  along  the  buccal  portion  of  the 
barrel,  marking  it  slightly  above  the  gum  line  and  between  the  adjoin- 
inii;  natural  teeth  along  the  line  of  exposure.  A  fine  saw  is  used  to  cut 
away  the  buccal  walls  to  these  lines.    The  palatal  wall  of  the  barrel  is 

cut  down  if  necessary  to  admit  the 
face,  so  that  it  will  articulate  with 
the  antagonizing  teeth.  Should  there 
be  any  lack  of  correspondence  be- 
tween the  outlines  of  the  barrel  top 
and  the  cusp  crown  or  tooth,  the 
gold  is  bent  to  fit  the  latter  accurately.  Ey  means  of  fine-grit  corun- 
dum wheels  the  edges  of  the  porcelain  are  closely  adapted  to  the  cut 
eclges  of  the  gold  at  the  cervical  and  approximal  borders,  and  articu- 
lated perfectly  with  the  antagonizing  teeth.  The  tooth  and  barrel  may 
now  be  set  with  cement:  it  is  preferable,  however,  to  solder  the  porce- 
lain to  the  barrel.  A  piece  of  24-carat  gold  No.  33  is  fitted  as  a  stay  to 
the  under  surface  of  the  porcelain  and  burnished  into  accurate  contact. 
The  tooth  and  stay  are  set  in  the  barrel,  and  the  latter  is  cut  away  at 
points  interfering  with  its  correct  placement.  It  is  boiled  in  the  acid 
solution,  and  invested  so  that  the  interior  of  the  barrel  and  the  stay  ex- 
posed form  a  concavity.    Borax  is  painted  around  the  line  of  junction  and 


Fic.  657 


- — 4--^' 


Cusp  crowns. 


over  the  pins,  a  small  piece  of  solder  placed  over  each  pin,  and  three  or 
four  pieces  around  the  joint,  and  the  piece  is  graduall}  raised  to  a  high 
heat;  a  fine  flame  directed  into  the  concavity  fuses  the  solder,  uniting 
the  piece;^  perfectly. 

In  finishing  the  crown  the  gold  should  be  dressed  down  to  the  porce- 
lain, making  a  perfectly  smooth  joint.  No  projection  of  the  gold  be- 
yond the  surface  of  the  porcelain  should  remain. 

Fused  porcelain  may  be  used  in  lieu  of  solder  to  attach  the  crown 
to  the  barrel,  as  described  by  Dr.  Robert  Huey:  "The  barrel  is  fitted 
and  cut  out  as  descrilied.  One  of  Ash  &  Sons'  diatoric  teeth  is  selected 
and  fitted  to  the  barrel.  Openings  are  drilled  through  the  mesial  and 
distal  walls  of  the  barrel,  which  shall  exactly  uncover  the  openings  of 
the  tube  in  the  tooth.  A  piece  of  platinum  wire  is  thrust  through  holes 
and  tube,  holding  the  porcelain  to  the  gold.     The  platinum  wire  is  now 


PORCELAIN  JACKET  CROWNS.  699 

either  riveted  or  soldered  to  the  barrel  The  hue  of  jiinetioii  between 
o-old  and  porcelain  is  painted  with  a  paste  of  dental  glass,  which  is  then 
fused  in  a  Downie  furnace." 

Dr.  W.  A.  Capon  claims  excellent  results  for  a  platinum  and  porce- 
lain jacket  crown,  the  details  of  the  construction  of  which  are  as  follows: 

"This  crown  is  made  by  fitting  a  platinum  band  (gauge  No.  31)  to  the 
root  of  prepared  tooth  (Fig.  658)  in  the  same  way  as  with  gold  cap  work, 
except  that  the  joint  must  have  overlapping  instead  of  abutting  edges. 
The  lingual  and  labial  outlines  of  the  adjacent  teeth  are  marked  on  the 
tube  (Fig.  659),  as  a  guide  to  grinding  those  portions  away  to  gain  shape 
instead  of  cutting  with  scissors.  The  lingual  side  is  shaped  with  a 
wheel  on  the  lathe  and  a  piece  of  the  same  gauge  platinum  soldered  to 
fit  it  with  very  small  amount  of  pure  gold.     (Fig.  660  and  661.)     After 

Fig.  658     Fig.  659       Fig.  660        Fig.  661      Fig.  662      Fig.  663 


trimming  and  fitting  to  the  root,  the  labial  surface  is  ground  thin  enough 
to  burnish  and  fit  over  the  tooth  (Fig.  662),  after  which  a  thin  porcelain 
veneer  is  fitted  and  held  in  position  by  the  porcelain  paste.  It  is  care- 
fully dried  and  baked  in  the  same  way  as  other  porcelain  crowns.  The 
crown  is  now  fitted  to  the  root  and  its  requirements  noted,  such  as  pro- 
per size,  shape  and  thickness.  If  the  surface  of  the  veneer  requires  grind- 
ing, it  should  be  done  at  this  stage,  so  that  it  will  be  glazed  again  by  the 
last  heat,  which  should  be  strong  and  of  uniform  degree.  After  final 
baking  the  platinum  portion  is  polished  and  the  crown  is  ready  for  set- 
ting, using  thin  cement  and  very  gentle  pressure  (Fig.  663.)  The  crown 
should  fit  easily,  as  there  is  danger  of  breaking  the  thin  porcelain  on 
the  sides  of  the  crown,  or  of  even  checking  the  veneer  itself. 

The  joints  are  lapped  and  made  as  close  as  possible,  so  that  great  and 
frequent  heating  will  not  entirely  destroy  the  union ;  any  excess  of  sol- 
der will  flow  over  the  surface  of  the  platinum,  and  destroy  the  porcelain 
adhesion,  which  may  not  be  noticed  at  the  time  of  the  operation,  but  will 
be  more  forcibly  noted  later  on.  The  lingual  surface  is  ground  thin  to 
give  shape,  so  that  there  may  be  two  flat  surfaces  to  hold  porcelain. 
When  finished  it  gives  the  proper  tooth  contour." 


7QQ  ARTIFICIAL  CROWXS. 


BAND  AND  PIN  CROWNS. 

While  a  pin  and  plate  crown  or  any  of  the  manufactured  crowns  are 
especially  adapted  for  temporary  work,  where  permanent  oj)erations 
are  desired,  the  root  should  always  be  banded  so  as  to  reduce  to  a  min- 
imum the  possibility  of  a  fracture.  It  is  always  best  to  be  on  the  safe 
side  in  the  beginning  and  to  treat  a  root  so  that  there  is  no  possibility, 
or  at  least  a  very  remote  one,  of  trouble  of  this  kind.  Of  all  the  crowns 
placed  in  the  anterior  part  of  the  mouth  in  which  the  roots  are  banded, 
the  Richmond  crown  is  the  one  which  is  most  frequently  used  and  is 
made  as  follows: 

The  root  having  been  properly  prepared  as  already  described  and  the 
band  fitted  to  it,  the  latter  is  marked  around  its  inside  and  cut  off  flush 
with  the  top  of  the  stump,  which  should  be  about  one  thirty-second  of 
an  inch  under  the  o-um  on  the  labial  side  and  about  one-sixteenth  of  an 

Fig.  664  Fig.  665  Fig.    666  Fig.  667 


inch  above  it  on  the  palatal.  A  floor  of  No.  30  coin  gold  is  then  sweated 
or  soldered  to  the  band.  It  is  now  replaced  on  the  root  and  a  hole 
made  in  the  floor  over  the  enlarged  root-canal  for  the  reception  of  the 
pin,  which  latter  is  preferably  made  of  platinized  gold.  This  is 
placed  in  position  and  fastened  with  adhesive  wax  (Fig.  664),  removed, 
invested  and  soldered.  It  is  then  put  back  on  the  root  and  the  impres- 
sion and  articulation  taken,  after  which  the  cast  is  prepared  in  a  manner 
already-described.  After  separating,  the  cap  is  removed  from  the  cast 
with  a  pair  of  heated  pliers  and  the  floor  on  the  labial  side  of  the  pin  is 
ground  or  filed  perfectly  flat.  It  is  then  replaced  on  the  cast,  and^a 
suitable  facing  selected  and  ground  to  fit  the  floor  of  the  cap.  (Fig.  665.) 
A  backing  of  thin  platinum  or  crown  metal  is  then  made,  extending 
from  the  floor  of  the  cap  to  about  one  sixteenth  of  an  inch  above  the  tip 
(Fig.  666.)  The  facing  is  then  waxed  in  place  with  adhesive  wax,  and 
when  this  is  nearly  hard,  it  is  pressed  tightly  against  the  backing  to  bring 
them  into  close  contact.  The  crown  is  now  removed  from  the  cast,  in- 
vested and  solderefl.  The  investment  should  be  made  to  cover  the 
band  partly  and  take  in  the  backing  which  expends  beyond  the  cutting 
edge,  thus  holding  it  down  and  preventing  it  from  drawing  away  from 
the  facing  in  soldering.     (Fig.  667.) 

A  favorite  and  easy  way  of  setting  in  the  facing,  is  to  grind  it  away 
so  that  only  the  tip  of  it  touches  the  floor  of  the  cap  at  its  outer  edge,  and 
then  to  let' the  backing  extend  all  the  way  to  the  end  of  the  facing,  and 


BAND  AXD  Piy  CROWNS. 


701 


fill  it  in  with  solder.  (Fig,  668.)  The  principal  objection  to  this 
method,  is  that  in  many  cases  the  gold  can  be  seen  from  the  front  or 
side  of  the  mouth,  or  there  is  a  dark  shadow  between  the  teeth  toward 
the  gingival  portion  of  the  crown,  which  renders  it  unsightly  and  un- 
natural in  appearance. 

In  the  making  of  the  so-called  Downie  porcelain  crown,  where  a 
facing  is  used,  the  band  and  cap  are  made  in  the  same  way  as  for  a 
Richmond,  with  the  exception  that  iridio-platinum  plate  No.  32  gauge, 


Fig.   668 


Fig.  669 


is  used  instead  of  gold  and  the  band  is  cut  lower  on  the  palatal  side. 
For  these  crowns  it  is  well  to  have  only  the  tip  of  the  facings  touch  the 
outer  edge  of  the  cap,  as  this  permits  the  porcelain  body  to  be  worked 
under  the  facing  better  than  when  it  is  close  to  the  floor.  (Fig.  669.) 
The  Half-cap  Crown.— While  the  full  Richmond  crown  in  point  of 
strength  and  impermeability,  may  justly  be  considered  as  the  ideal 
crown,  the  one  serious  objection  to  it  is  the  difficulty  of  conceahng  the 
labial  portion  of  the  collar.     No  method  of  crown  construction  can  be 


Fig.  670 


Fig.   671 


said  to  be  perfect  which  allows  any  of  the  metalhc  portion  to  be  visible 
after  it  is  permanently  fixed.  For  this  reason  a  large  number  of  crowns 
which  are  set  on  upper  anterior  roots  are  constructed  on  the  half-cap 
plan.  When  the  half-cap  is  accurately  fitted  at  the  lingual  aspect,  it  is 
nearly  as  strong  as  would  be  a  full  cap  or  collar.  An  additional  advan- 
tage will  also  be  found  in  the  fact  that  the  use  of  the  half-cap  ob\dates 
the  necessity  of  forcing  the  collar  under  the  gingival  margin  at  the 
labial  portion  to  such  an  ex-tent,  in  orderto  get  it  out  of  sight,  that  perios- 
teal disturbances  may  result.     As  shown  by  Fig.  670,  in  the  absence  of 


702 


ARTIFICIAL  CROWNS. 


liiiijual  ivinf()rccment,the  post  bocomos  a  lever,  and  its  foree  is  exerted 
from  the  centre  of  the  root  and  falls  upon  its  labial  or  bueeal  half,  re- 
sultino-  eventually  in  splitting  of  the  root.  The  half-cap,  as  shown  by 
Fi'i-.   671,  places  the  reinforcement  where  it  is  most  needed,  while  it 


Fig.  672 


admits  of  so  nice  an  adjustment  of  the  porcelain  facing  that  its  neck 
may  be  made  to  pass  far  enough  under  the  gum-margin  to  simulate 
closely  the  appearance  of  the  adjoining  natural  teeth.     Much  of  the 


Fig.  673 


preliminary  work  in  the  construction  of  such  a  crown  may  be  done  on  a 
good  ]:>hister  cast.  The  root  should  first  be  prepared,  including  the 
enlargement  of  the  canal  for  the  reception  of  the  post;  the  latter  is  then 
placed  in  position  and  a  plaster  impression  obtained.     The  plaster 


READY-MA DE  CRO WNS. 


7u:i 


cast  re(iuircs  no  modification,  except  that  the  phister  should  be  cut  away 
at  the  gum-margin  of  the  hngual  aspect,  as  shown  by  Figs.  672  and  673, 
to  enable  the  operator  to  carry  the  half-collar  slightly  under  the  gum 
(Fig.  674.)  The  half-collar  should  be  accurately  fitted  to  the  convexity 
of  the  remaining  portion  of  the  crown  and  as  much  of  the  root  as  it 
embraces;  the  floor  of  the  cap  is  then  made  and  soldered  to  the  pin. 
The  collar  portion  of  the  cap  is  then  to  be  tacked  to  the  floor  by  a  minute 
particle  of  solder,  as  shown  by  Fig.  675;  the  cap  should  then  be  tried 
upon  the  root  to  ascertain  whether  the  adjustment  is  perfect,  and  to  im- 
prove it,  if  necessary,  by  pressing  the  edge  of  the  collar  to  complete  con- 
tact with  the  root  at  the  gingival  margin  with  a  burnisher.     After  which 


Fig.  674 


Fig.  675 


Fig.  676 


the  collar  and  flat  piece  with  the  post  are  united  by  the  smallest  amount 
of  solder  practicable.  The  selecting  and  fitting  of  the  porcelain  tooth  to 
the  cap  and  the  subsequent  soldering  and  finishing  are  the  same  as  in 
the  full  Richmond  crown.     Fig.  676  shows  the  completed  crown. 

READY-MADE   CROWNS. 


Of  the  ready-made  porcelain  crowns  there  are  two  varieties — first, 
those  designed  for  fixation  upon  a  post  which  is  previously  fastened  in 
the  root;  second,  those  having  a  pin  baked  in  them.  To  the  first  class 
belong  the  Bonwill,  the  Davis,  the  S.  S.  White  detachable  pin  crown, 
the  Fellowship  and  various  others  on  the  market :  in  the  second  class 
are  included  the  Logan,  the  Brewster  and  several  others.  Crowns 
which  are  formed  and  adapted  by  means  of  sets  of  ready-made  appli- 
ances, such  as  the  Hollingsworth  and  the  mandrel  systems,  belong  to 
the  class  of  built-up  crowns. 

Of  the  ready  made  porcelain  crowns,  the  Davis,  and  S.  S.  White  de- 
tachable post  crown  are  those  having  the  widest  range  of  usefulness. 
The  methods  of  fitting  and  mounting  them  are  similar,  and  as  a  de- 
scri])tion  of  the  technique  of  these  operations  would  applv  equally  well 
to  all,  the  following  is  quoted  from  Dr.  G.  W.  Schwartz  concerning  the 
use  of  the  Davis  crown. 


704 


ARTIFICIAL   CROWNS. 


Rapid  Method  of  Setting  Davis  Crown. — "We  shall  first  consider  the 
easiest  and  most  rai)i<l  nirthod  of  setting  the  Davis  crown,  which  is  as 
follows:  ha\ing  the  root  properly  prepared  to  crown,  grind  it  even 
with  the  gum  line  and  enlarge  the  canal  to  receive  the  post.  Next, 
cement  it  in  place  in  the  root.  Now  select  a  suitable  crown  and  cement 
it  to  the  post  as  shown  in  Figs.  677  and  678.  If  you  prefer,  you  may 
cement  the  post  in  the  crown  first  and  then  the  crown  and  post  may  be 
cemented  to  the  root,  or,  you  may  cement  the  crown  to  the  post  and  the 


Fig.  677 


Fig.   678 


Fig.  679 


post  in  root  at  the  same  time  if  you  choose,  with  results  shown  in  Fig. 
678. 

If  you  wish  to  follow  a  more  conservative  method  of  setting  this  crown 
without  banding  the  root,  I  would  suggest  that  the  root  be  ground  at  a 
bevel  from  the  lingual  margin  to  the  centre  of  the  root,  as  shown  in  Fig. 
()79.  This  preparation  of  the  root,  by  reason  of  the  bevel  from  the 
lingual  margin  to  the  centre  of  the  root,  prevents  liability  to  displace- 


Fig.  680 


Fig.  681 


Fig.  682 


Fig.  683 


ment  from  stress  of  mastication  or  incising  force;  also  any  possibility 
of  splitting  the  root  from  the  same  cause.  The  concavity  from  the 
labial  margin  of  root  to  the  centre  gives  plenty  of  room  for  thickness  of 
porcelain,  thus  insuring  its  color. 

The  next  step  is  to  cement  the  post  in  place  to  the  root  and  select 
your  crown.  After  the  cement  has  set  sufficiently  not  to  disturb  the 
post,  you  can  begin  grinding  your  porcelain  in  place.  This  may  be 
done  as  follows:  first,  grind  it  to  fit  as  nearly  as  possible,  then  insert  a 
thin  piece  of  carbon  paper  around  the  post  so  that  it  will  come  between 


READY-MADE  CROWNS.  705 

the  root  and  porcelain,  as  shown  in  Fig-.  OSO;  by  nsin<;-  a  Httle  rotary 
pressure,  the  carbon  will  leave  little  marks  on  the  porcelain  wherever 
it  touches  it.  Grind  until  the  surface  is  evenly  marked  by  the  carbon. 
With  a  little  care  a  very  close  adaptation  can  be  had  by  this  method. 
When  the  porcelain  is  properly  ground,  dry  the  post  and  root  and  cement 
in  place,  which  completes  this  operation,  as  shown  in  Fig.  G81. 

Gold  Banded  Roof. — Grind  the  root  evenly  to  the  gum  margin,  remov- 
ing all  enamel  from  it,  thus  giving  the  labial  portion  of  the  root  a  slight 
bevel.  This  bevel  is  for  the  purpose  of  covering  the  band  by  closely 
grinding  the  porcelain  crown  to  it,  as  shown  in  Figs.  682  and  683. 

Having  the  root  prepared  and  the  canal  enlarged,  take  a  measure- 
ment of  the  root,  cutting  the  band  snug  that  it  may  take  the  beveled 
shape  when  fitted  on.  After  the  band  has  been  properly  fitted,  solder 
the  cap,  then  fit  the  post  in  and  solder  them  together  as  in  Fig.  682. 
Now  replace  the  cap  on  the  root  and  you  are  ready  to  grind  in  the  porce- 
lain. Another  way  is  to  take  an  impression  at  this  point  and  run  a 
model  with  the  cap  in  place,  using  the  model  to  work  with  rather  than 

Fig.  6S4  Fig.  6S5 

A 


the  patient.  In  this  case  grinding  in  the  porcelain  gives  the  dentist  a 
chance  of  showing  his  skill.  It  is  a  clever  piece  of  work,  requiring  some 
patience  when  neatly  ground  in,  but  one  which  repays  in  satisfactory 
results.  I  use  small  corundum  stones  of  difterent  grits  to  do  my  first 
grinding.  The  fine  grinding  is  done  with  a  rubber  corundum  point 
mounted  with  jeweler's  cement  in  a  smooth  porte  polisher.  After  the 
porcelain  is  correctly  ground,  cement  the  crown  to  its  place  on  the  cap 
allowing  it  to  set  out  of  the  mouth.  Finally  cement  it  to  the  root  in  the 
usual  manner  or  set  it  with  gutta-percha.  Fig.  683  shows  this  crown 
finished. 

In  Porcekiin. — Platinum  Matri.v  Without  Band. — Prepare  root  as 
shown  in  Fig.  689,  Take  a  piece  of  soft  platinum  plate,  36  gauge  or  less, 
and  burnish  this  over  the  root  until  its  margins  are  distinctly  outlined. 
(Fig.  684.)  Punch  a  hole  in  this  matrix  where  the  post  should  go,  using 
a  plate  punch.  Take  an  iridio-platinum  post  and  push  it  into  place  in 
the  root-canal  through  the  hole  made  in  the  matrix.  Now  remove  the 
matrix  and  post  together,  and  solder.  Pure  gold  will  do  to  solder  in  this 
case.  Replace  matrix  on  root  and  burnish  to  place  again.  By  trim- 
ming oft'  all  excess  platinum,  you  will  have  a  matrix  following  the 
marginal  outline  of  the  root.  (Fig.  685.)  You  are  now  ready  to  select  the 
porcelain  crown  to  be  baked  to  this  post  and  matrix.  Grind  the  porcelain 
to  fit  matrix  as  shown  in  Fig.  686.    Put  some  thin  body  in  the  post  hole 

45 


706  ARTIFICIAL  CROWNS. 

of  the  crown,  being  careful  to  work  it  to  place  on  the  pin.  Let  it  dry. 
Then  put  the  crown  on  a  crown  tray  with  two  small  rolls  of  asbestos 
under  the  matrix  as  shown  in  Fig.  687 ,  These  rolls,  one  on  each  side 
of  the  post,  prevent  the  matrix  from  coming  in  contact  with  the  tray  and 
to  obviate  the  danger  of  its  changing  shape  or  fusing  to  the  tray.  You 
are  now  ready  to  put  it  through  its  first  baking.  This  should  not  be 
carried  beyond  a  good  biscuit.  After  the  first  bake,  try  it  in  the  mouth 
to  see  that  it  is  correct.  If  the  porcelain  needs  grinding  to  conform  to 
the  outline  of  the  matrix,  as  it  usually  does,  do  so  before  the  second 
baking  and  polish  the  ground  surfaces  with  disks;  remove  all  foreign 
substances  from  the  case  by  careful  cleansing  and  after  filling  the  spaces 
beneath  the  matrix  with  porcelain  body,  bake. 

If  the  work  has  been  thoroughly  done,  this  should  complete  it  and  it 
should  come  out  of  the  furnace  a  beautiful  piece  of  work.     As  the  ma- 

FiG.  6S0 .  Fig.  687 .  Fig. 688 . 


trix  has  now  served  its  purpose  it  should  be  removed.  If  it  were  left  on 
the  crown,  it  would  have  a  tendency  to  produce  a  blue  shade  at  the  neck 
which  is  to  be  avoided.  To  remove  the  matrix,  take  a  small,  round  bur 
and  drill  through  it  close  to  and  around  the  post.  Next,  take  a  sharp 
pointed  excavator  and,  beginning  at  the  lingual  margin,  continue  to 
raise  the  matrix  up  until  the  entire  matrix  comes  away  from  the  crown. 
This  crown  should  resemble  Fig.  688  when  cemented  in  place. 

Platinum  Band,  Iridio-Platinvm  Post.  Prepare  the  root  for 
this  crown  in  the  manner  illustrated  in  Fig.  682.  The  metal  work 
is  done  by  the  same  method  but  with  the  following  difference  in 
materials :  platinum  is  used  instead  of  gold  for  the  cap  and  band  and 
an  iridio-j)latinum  post  is  substituted  in  this  case  for  the  Davis 
post  used  in  the  other.  The  reason  for  this  substitution  of  plat- 
inum is  obvious.  This  crown  is  to  be  put  through  the  furnace.  Hav- 
ing proceeded  to  the  point  of  having  the  platinum  cap  and  post  in  place 
on  the  root,  take  the  bite  and  a  plaster  impression,  melt  a  small  quantity 
of  wax  in  the  platinum  cap  and  run  the  casts.  This  placing  of  wax 
in  the  cap  facilitates  the  removal  of  the  latter  from  the  cast.  Before 
going  farther  it  is  well  to  see  that  the  wax  is  out  of  the  cap  and  that  the 
cap  goes  on  and  comes  off  the  cast  easily.  After  placing  the  cap 
again  on  the  cast  you  may  proceed  to  grind  in  the  crown. 


READY-MADE  CROWNS. 


707 


Fig.  689 


For  the  purpose  of  getting  porcelain  body  in  for  the  last  baking,  two 
V-shaped  spaces  should  be  ground  in  the  crown,  one  mesially  and  one 
distally;  Fig.  689.  When  properly  ground  and  ready  for  the  first  bake, 
the  crown  should  touch  the  cap  at  a  labial  and  at  a  lingual  point. 

To  fasten  the  crown  and  cap  together  for  the  first  bake,  put  some 
thin  body  in  the  post  hole  of  the  crown,  carefully  letting  it  settle  to  place 
on  the  post  and  cap.  After  allowing  this  to  dry,  gently  remove  it  from 
the  cast,  place  it  on  a  crown  tray  for  the  purpose  and  biscuit  it  in  the 
furnace. 

When  it  has  gone  through  the  furnace  for  the  first  time,  try  it  in  the 
mouth   and   then  do  the   necessary  grinding  and  polishing. 
Before  baking  for  the  last  time   it   should    be   thoroughly 
cleansed  and  the  porcelain  body  packed  into  the  case  in  such 
a  manner  as  to  give  it  the  proper  contour. 

There  are  two  strong  points  in  favor  of  these  crowns  which 
it  might  be  well  to  mention.  The  first  is,  there  is  no 
soldering  to  be  done  where  there  is  danger  of  checking 
porcelain.  The  second  is,  they  are  easily  repaired  when 
broken  in  the  mouth. 

Lastly,  when  a  patient  comes  to  you  with  a  Logan  post 
fast   in   the    root,  grind  in  a  Davis  crown  and  cement  it  in  place." 

The  system  of  porcelain  and  jacket  crowns  of  Dr.  C.  H.  Land  of 
Detroit,  Mich.,  is  similar  to  the  above,  only  in  that  the  pin  is  first  per- 
manently fastened  into  the  root;  in  other  respects  it  admits  of  more 
precise  adjustment  and  is  more  durable.  The  principle  involved  in 
the  construction  of  a  Land  crown  differs  from  all  ordinary  methods  in 
the  following  particulars:  "The  post,  or  screw,  is  firmly  fixed  in 
the  root  by  cement  or  amalgam  (A),  then  a  tube  with  flange  (B)  is  put 


Fig.  690 


on  the  post  and  the  flange  burnished  or  malleted  to  conform  to  the  sur- 
face of  the  root,  and  trimmed  to  its  exact  contour  (C).  A  pinless  veneer 
(D)  is  then  baked  on  this  'matrix'  or  tube.  This  makes  a  tube  tooth  in 
fact  which  is  cemented  on  the  post  and  root.  Flat  back  teeth  or  facings 
may  be  used  instead  of  the  pinless  veneers  and  the  pins  soldered  to  the 
tube  (E).  F  and  G  show  finished  crowns.  In  case  of  breakage,  the 
porcelain  crown  can  be  removed,  leaving  the  post  in  the  root,  a  new 
facing  can  be  baked  on  and  contoured  and  cemented  on  the  root  as  be- 


708  ARTIFICIAL  CROWNS. 

fore.  This  avoids  tlie  necessity  of  removing  tlie  post  from  the  root." 
The  Custer  or  Downie  furnace  may  be  used  in  fusing  the  porcehiin  in 
the  construction  of  these  crowns. 

The  next  class  of  crowns  is  composed  of  those  having  their  platinum 
posts  baked  in  them :  they  are  the  Logan,  the  Brewster  and  several 
others  of  this  type. 

The  first  of  these  has  the  widest  range  of  application,  and  is  the  form 
in  most  general  use.  Being  composed  of  porcelain  alone,  and  having 
no  underlying  mass  and  backing  of  metal,  they  present  a  translucent 
appearance  not  to  be  had  with  those  forms  of  crown  which  are  built  up 
in  part  of  metal.  An  excellent  method  of  selecting  and  adapting  these 
crowns  is  as  follows:  the  root  face  is  trimmed  by  means  of  rotatory 
files  or  the  Ottolengui  root-facers,  to  the  level  of  the  gum  margin.  The 
canal  is  sterilized,  and  the  upper  third  hermetically  sealed,  the  remain- 
der of  the  canal  enlarged  to  about  one-sixteenth  of  an  inch  in  diameter. 
A  wax-bite  is  taken,  including  several  of  the  adjoining  teeth.  A  piece 
of  iron  wire  one-half  of  an  inch  longer  than  the  reamed  portion  of  the 

canal,  and   small    enough  to  slip  very 
^'^  ^'-^i  freely  in  it,  has  its  end  bent  into  a  loop 

and  the  canal  portion  covered  with 
gutta-percha,  wdiich  is  then  oiled  and 
slipped  in  the  root  A  plaster  impres- 
sion is  taken  in  which  the  coated  wire 
is  withdrawn, and  a  cast  made  of  fusible 
metal  melting  at  about  150°  F.  A 
shade  tooth  and  a  crown  corresponding 
with  the  natural  teeth  are  selected.  The 
direction  of  the  axis  of  the  root-canal 
is  noted,  and  the  angle  which  it  makes 
with  the  root  face  compared  with  the  direction  of  the  axis  of  the 
selected  crown :  not  infrequently  it  is  necessary  to  bend  the  pin  at  an 
angle  with  the  axis  of  the  crown  itself  (Fig.  691).  The  opening  in  the 
root,  made  by  withdrawing  the  gutta-percha  and  wire,  is  enlarged 
sufficiently  to  receive  the  post  of  the  crown. 

The  pin  is  bent,  if  necessary,  so  that  the  axis  of  the  crown  is  parallel 
with  that  of  the  natural  fellow,  bringing  the-cutting  edge  of  the  artificial 
crown  in  the  arch  of  the  natural  teeth.  The  })oints  of  contact  between 
the  edges  of  the  crown  and  the  face  of  the  root  represented  in  the  me- 
tallic cast  are  ground  from  the  porcelain  until  there  is  a  uniform  con- 
tact throughout  the  crown  edge.  The  grinding  is  done  by  means  of 
square-edged  corundum  wheels  on  a  laboratory  lathe  or  by  an  engine 
wheel,  as  shown  in  Fig.  692.  The  cutting  edge  of  the  artificial  crown 
should  exactly  repair  the  break  in  the  arch.  Its  palatal  surface  is  cut 
away,  if  necessary,  to  articulate  with  the  antagonizing  teeth,  in  which 
event  the  cut  surface  should  be  smoothed  and  polished.  The  canal  is 
enlarged  by  means  of  fissure  burs  or  Ottolengui's  reamers  (Fig.  603) 
until  the  pin  slips  readily  into  place  and  the  surfaces  of  crown  and  root 
are  in  contact.     Should  either  the  edge  of  the  crown  or  the  edge  of  the 


READY-MADE  CROWNS. 


709 


root  project  beyond  the  coininou  line  at  any  point,  it  is  to  be  trimmed 
down  until  the  line  of  junction  is  uniform.  Any  slight  imperfections  of 
contact  are  to  be  remedied  by  means  of  the  carbon-paper  test:  small 
pieces  of  this  mateial,  large  enough  to  cover  the  face  of  the  root,  are 
pressed  to  its  surface  and  perforated  by  the  crown  post.     The  crown 


Fig.    692 


Fig.  693 


S 


is  now  pressed  firmly  into  position  and  withdrawn :  should  there  be  any 
breaks  in  the  black  line,  the  crown  is  dressed  down  at  all  parts  marked 
until  there  is  a  continuous  black  line  at  the  outer  edge  of  the  crown. 

The  crowns  may  be  accurately  adapted  to  the  roots  without  the  use 
of  a  model,  but  as  it  is  desirable  to  make  a  model  to  serve  as  a  guide  in 


Fig.  694 


Fig.  695 


Prepared  articulating  paper. 


selecting  a  crown  of  the  proper  size  and  form,  the  same  model  may  fur- 
nish a  base  and  guide  for  adapting  it.  The  operation  described  in  real- 
ity saves  time. 

In  fitting  these  crowns  without  a  model  the  canal  is  enlarged  suf- 
ficiently to  receive  the  metallic  post,  the  root  surface  trimmed  to  the 


710  ARTIFICIAL  CROWNS. 

proper  form  by  means  of  the  root-facers,  and  the  crown  is  fitted  as 
follows : 

Dr.  E.  C.  Kirk's  Method  of  Fitting  a  Logan  Crown  to  a  Tooth-root.* 
— Cut  several  small  pieces,  about  one-cjuarter  inch  square,  from  a 
strip  of  thin  articulating  paper.  In  the  centre  of  each  punch  a  hole 
with  the  tool  shown  in  the  margin.  Having  prepared  the  root-end, 
slip  the  perforated  piece  of  articulating  paper  over  the  pin  of  the  Logan 
crown  and  press  it  firmly  into  position,  in  contact  with  the  root.  Upon 
withdrawing  the  crown  and  removing  the  articulating  paper,  the  points 
of  contact  will  be  found  to  be  marked  black.  Grind  these  off  carefully, 
readjust  on  the  root  as  before,  grind  again,  and  continue  the  operation 
of  fitting  and  grinding  until  the  mark  made  by  the  articulating  paper  on 
the  contact  surface  of  the  crown  presents  as  a  uniformly  unbroken 
black  ring.  When  this  has  been  accomplished,  the  crown  will  be  found 
to  fit  the  root-end  with  the  utmost  accuracy.  The  advantages  of  fitting 
a  crown  directly  to  the  root  are,  it  would  seem,  self-evident  from  the 


mechanical  standpoint,  and  involve  besides  the  least  expenditure  of 
time.^ 

A  Method  for  Perfectly  Adjusting  the  Logan  Crown. — "By  making 
a  considerable  change  in  the  present  form  of  the  Logan  crown,  as  shown 
in  Fig.  696, 1,  A  and  B,  we  have  a  crown  that  can  be  adjusted  in  a  few 
minutes,  and  with  a  degree  of  perfectness  not  yet  obtainable  by  any 
crown  on  the  market,  nor,  within  my  knowledge,  by  any  so  far  sug- 
gested method. 

"The  manner  of  making  the  adjustment  is  certainly  as  simple  as 
could  be  desired. 

"After  preparing  the  canal  for  the  reception  of  the  'Logan  pin,'  select 
a  tooth  in  the  usual  way,  having  regard  to  correct  length,  width,  and 
color,  and  if  care  has  been  exercised  to  select  one  as  near  the  right  length 
as  possible,  it  will  only  be  necessary  to  touch  the  buccal  ar  labial  point 
of  the  neck  of  the  crown  a  few  times  with  the  corundum  wheel,  and  the 
proper  length  or  bite  will  be  obtained.  Next  take  a  disk  or  small  piece 
of  thin  platinum  foil,  about  No.  50,  and  push  through  this  the  pin  of 
the  tooth,  carrying  the  disk  up  against  the  porcelain,  as  represented  in 
Fig.  969,  3.  With  a  little  drop  of  Parr's  fluxed  wax  dropped  in  the 
triangular  space,  formed  by  the  backing  and  the  pin,  the  disk  is  held 

'  Dental  Cosmos,  June,  1894. 


READY-MADE  CROWNS.  711 

securely  in  place,  and  the  platinum  is  trimmed  around  with  small  scis- 
sors, that  there  may  not  be  any  overlapping.  Now  place  around  the 
pin  on  the  platinum  a  ball  of  Parr's  wax,  stick  the  pin  through  the  sec- 
ond disk  of  the  foil,  and  rub  the  platinum  with  a  hot  instrument,  that 
the  wax,  and  disk  may  be  sealed  together,  as  shown  in  Fig.  69G,  4. 
Place  this  in  ice-water  to  harden  the  wax,  so  as  to  resist  pressure.  It  is 
now  ready  to  insert,  and  by  pressing  the  tooth  up  until  the  labial  sur- 
face strikes  the  end  of  the  root,  and  having  the  patient  to  close  the  jaws, 
the  correct  bite  will  be  secured  with  the  opposite  tooth.  It  will  be  found 
on  the  removal  of  the  crown  that  the  platinum  next  the  root  has  been 
perfectly  swaged  to  the  root-end.  This  second  disk  is  now  trimmed 
according  to  the  outlines  of  the  root.  When  it  is  so  desired,  the  pala- 
tal side  of  the  root  having  been  left  a  little  high,  or  just  above  the  gum, 
the  platinum  can  be  split  with  scissors,  lapped,  and  burnished  around 
the  exposed  side  of  the  root,  to  form  a  partial  band  (Fig.  696,  5). 

"After  having  dried  the  wax  with  bibulous  paper  and  shaped  up  the 
approximal  sides,  these  sides  are  covered  with  small,  triangular  pieces 
of  platinum  (Fig.  696,  6)  by  lapping  the  platinum  on  the  wax  and  rub- 
bing over  it  a  hot  burnisher.  The  crown  is  now  ready  to  invest,  an 
the  investing  mixture  is  poured  on  a  small  piece  of  wire  netting,  which 
will  prevent  its  cracking  during  the  soldering  operation.  The  wax  hav- 
ing been  burned  out,  this  triangular  box  is  filled  flush  with  solder  in  the 
usual  way  and  polished.  The  result  is  a  beautiful  and  perfect  crown, 
in  every  respect  the  most  substantial  porcelain  crown  w^e  have. 

"I  frequently  make  the  crown  without  using  the  triangular  piece  of 
platinum  to  form  the  box  (Fig.  696,  5),  relying  on  the  investment  to 
form  the  sides.  This  saves  a  little  time;  but  it  frequently  happens,  un- 
less care  has  been  taken  to  make  the  wax  flush,  that  the  approximal 
surfaces  are  not  well  rounded,  and  consequently  do  not  finish  well.  It 
is,  therefore,  safer  to  use  the  triangular  pieces  of  platinum  foil  to  form 
the  sides  of  the  box,  as  described,  before  filling  with  solder.  This  plan 
is  particularly  adaptable  to  those  cases  of  fracture  wdiich  have  resulted 
in  a  rough  root-end,  and  where  it  is  often  next  to  impossible  to  get  them 
smooth. 

"Where  it  is  convenient  or  if  it  is  desired,  the  triangular  box  can  be 
filled  with  'body',  and  baked  in  a  Parker  furnace  from  six  to  eight 
minutes.  This  gives  us  an  all-porcelain  crown  which  fits  perfectly  to 
the  end  of  the  root.  In  this  case  the  first  disk  next  the  porcelain  is  left 
off  entirely."  ' 

Caution. — The  Logan  crown  contains  a  large  tapered  pin  wath  its 
large  end  baked  in  the  tooth,  and  when  heated  to  flow  solder  over  or 
around  it,  care  must  be  taken  that  the  porcelain  is  made  as  hot  as  or 
hotter  than  the  pin,  thus  preventing  uneven  expansion  and  cracking  of 
the  porcelain. 

These  crowns  may  be  adapted  upon  frail  roots,  which  demand  the 
supplementary  support   of  a  band  encircling  their  necks.      It  is  a 

^Gordon  White,  D.  D.  S.,  Dental  Cosmos,  January,  1893. 


712  ARTIFICIAL  CROWNS. 

matter  of  but  little  practical  moment  whether  the  collar  is  or  is  not 
attached  to  the  crown:  the  object  sought,  the  protection  of  the  root 
against  lomntudinal  fracture,  is  secured  by  banding  the  root  first,  form- 
inf  an  artificial  root  face  by  moans  of  metal.  The  root  face  is  trimmed 
as  for  a  collar  crown;  the  collar  is  fitted  and  a  cap  soldered  to  it,  the 
edo-e  of  the  top  being  hidden  at  its  labial  aspect  by  the  gum.  While 
the  cap  is  on  the  root  an  opening  is  made  in  it  considerably  larger  than 
the  size  of  the  crown  post.  A  piece  of  metal  longer  than,  and  slightly 
larger  on  its  sides  than,  a  full  Logan  post  is  greased  with  vaseline;  the 
root  is  dried,  zinc  phosphate  is  packed  into  it  for  more  than  half  its 
lenoih,  the  ferrule  partly  filled  by  the  same  mixture  and  pressed  into 
position.  AVltile  the  cement  is  soft  the  metal  wedge  is  thrust  into  the 
cement  as  deep  as  a  I>ogan  pin,  and  left  until  the  cement  hardens,  when 
it  may  be  readily  mthdrawn.  The  crown  is  now  adjusted  to  the  canal 
in  the  cement  and  to  the  edges  of  the  ferrule  top.  The  gold  of  the  cap 
mav  be  dressed  away,  together  with  a  portion  of  the  cement,  until  but  a 
narrow  retaining  rim  of  gold  is  left. 

Fig.  697  Fig.  698  Fig.  699 


Logan  crowns  adapted  after  this  manner  are  to  be  cemented  into 
position  as  follows:  an  appropriate  root  clamp  (Ottolengui's)  is  placed 
on  the  root,  and  the  rubber  dam  slipped  over  several  adjoining  teeth  and 
the  clamp.  The  root  is  well  dried  by  means  of  alcohol  and  the  hot 
blast;  the  canal  is  wiped  with  a  pellet  or  cone  of  paper  saturated  with 
the  cement  fluid  to  facilitate  the  flow  of  the  cement.  A  paste  of  cement 
is  made  just  thick  enough  to  be  formed  into  perfectly  plastic  pellets; 
one  of  these  is  rolled  into  a  cone,  and  before  the  latter  bends  by  its  own 
weight  it  is  carried  into  the  canal;  another  is  pressed  into  the  concavity 
in  the  base  of  the  tooth;  the  grooves  in  the  post  are  filled;  the  crown  is 
then  thrust  into  position  and  pressed  home,  when  the  cement  will  ooze 
from  the  edges,  and  the  joint  should  be  a  very  thin  line.  The  crown  is 
left  undisturbed  for  at  least  fifteen  minutes,  when  the  cement  will  be 
found  hard  enough  to  resist  fracture. 

Dr.  Hollingsworth's  Method  for  Accurately  Adapting  and  Mounting  a 
Logan  Crown  with  a  Band.. ^"Prepare  the  root  in  the  usual  way  for 
banding.     (See  Fig.  697,  front  view,  and  Fig.  698 .side  \'iew.) 


BEAD  Y-MA BE  CR 0  WNS. 


713 


"Grind  the  abiittiiifi;  surface  of  the  crown  to  fit  the  root  under  the 
free  margin  of  the  gum,  along  the  labial  face  only.  (See  Figs.  097  and 
698,  a  tob.) 

"  Cut  the  crown  away  slightly  at  the  lingual  surface,  so  as  to  leave  a 
space  between  it  and  the  end  of  the  root.     (See  Fig.  699,  c.) 

"INIake  a  band  only  wide  enough  to  give  a  good  ho  d  on  the  root,  but 
not  to  extend  beyond  margin  of  gum,  to  fit  the  root  and  trim  off  even 
with  the  end  of  it.  (See  Fig.  699,  d.)  After  fitting  the  band  properly 
remove  it  and  solder  a  piece  of  pure  gold  plate,  say  about  No.  34,  on 
the  outer  end.  (See  Fig.  699,  e.)  This  can  be  done  quickly  by  placing 
the  plate  in  the  hand  and  pressing  the  band  on  it  with  the  thumb  for  a 
fit,  then  soldering  in  the  flame  of  a  Bunsen  burner.  Punch  a  small 
hole  through  the  plate  to  take  the  pin  in  the  crown,  and  replace  in  posi- 
tion on  the  root  after  trimming  off  the  exposed  edges.  Now  take  a 
piece  of  thin  pure  gold,  say  No.  34  or  36,  with  ears  as  shown  in  Fig. 
700;  punch  a  hole  through  it,  slide  it  over  the  pin  of  the  Logan  crown, 


Fig  700 


Fig.  701 


Fig.  702 


and  burnish  tightly  to  the  base  of  the  crown.  (See  Fig.  700.)  Next 
warm  the  pin  and  place  a  sufficient  quantity  of  Parr's  fluxed  wax  around 
it  as  shown  by  dotted  lines.  Fig.  700.  Replace  the  Logan  crown  on  the 
root  (with  the  cap  in  position),  force  home  until  the  labial  edges  of  root 
and  crown  meet,  obtain  the  proper  alignment,  and  cool  and  harden  the 
wax  by  using  a  napkin  with  ice-water.  Then  remove  the  crown  and 
cap  together,  held  in  proper  relative  position  by  the  wax.  (See  Fig. 
70L)  Trim  off  the  surplus  wax  and  invest.  (See  Fig.  702.)  Remove 
all  the  wax  possible  between  the  crown  and  the  band,  and  flow  20-carat 
gold  solder  into  the  space.  The  wax  which  will  necessarily  remain, 
being  fluxed,  vdW  carry  the  solder  into  every  cre\H[ce  and  give  the  crowTi 
great  strength.  Finish  the  band  and  the  soldered  edges,  and  the  result 
will  be  a  strong  and  perfectly  aligned  crown. 

The  Hollingsworth  System  of  Orown-and  Bridge-work. — A  system  which 
affords  greater  range  of  ready  application  than  any  of  its  predecessors 
is  that  known  as  the  "Hollingsworth."  Its  claims  and  description  are 
thus  given  by  its  inventor : 

"This  system  supplies,  in  the  first  place,  a  variety  of  forms  for  the 
various  teeth  great  enough  to  cover  almost  anv  case  and  for  the  rare 
cases  which  cannot  be  suited  direct  it  affords  a  ready  means  of  making 


714 


ARTIFICIAL  CROWNS. 


1  lo.  703 


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m 


'T\  'T^  ^  N^  -^  )  *^i  w      ^    ^^      — .      _ 


:7  9. 


^^ii;#il: 


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THE  CASTING  PROCESS  IN  CROWN    WORK.  715 

the  exact  form  reciuired.  There  are  in  the  set  two  hundred  and  four 
forms  of  cusps  and  thirty-six  of  facings  for  bicuspids  and  molars,  and 
forty  forms  for  incisors  and  canines.  Tliese  last  give  both  the  labial  and 
lino-ual  faces.  All  the  forms  are  exact  facsimiles  from  nature,  selected 
with  great  care  to  cover  the  widest  range  possible.  They  are  made  of 
metal,  and  are  used  as  patterns  from  which  to  make  dies  or  molds,  as 
may  be  required,  for  the  swaging  of  gold  cusps  or  crowns.  There  is, 
therefore,  no  wear  upon  them,  and  they  retain  their  shapes  and  sizes  un- 
altered. 

"The  outfit  for  working  these  forms  consists  of  a  molding  plate, 
three  rubber  rings,  a  sheet  of  asbestos  10  by  7  inches,  a  carbon  stick  for 
use  in  casting,  and  a  box  of  Hollings worth's  annealed  copper  strips  for 
measuring  roots. 

"This  system  permits  cusps  to  be  made  either  hollow  or  soHd.  Scrap 
gold  can  be  used  for  casting  solid  cusps,  and  porcelain  facings  can  be 
quickly  inserted  in  crowns  without  investing;  but  perhaps  its  most  im- 
portant advantage  is  the  exactness  Tvnth  which  the  fit  and  articulation 
of  bridges  are  obtained  and  maintained." 

THE  CASTING  PROCESS  AND  ITS  AVAILABILITY  IN  CROWN  WORK. 

The  introduction  of  this  method  has  opened  up  a  large  field  in  this 
branch  of  prosthesis,  but  it  must  be  employed  with  a  full  recognition  of 
its  limitations.  Cast  gold  is  not  as  strong  as  rolled  gold,  and  a  bridge  of 
the  former  not  so  strong  as  one  built  up  and  soldered.  The  shrinkage 
of  the  metal  in  cooling  must  also  be  taken  into  account  or  failure  on  that 
score  is  sure  to  result. 

The  metal  used  for  this  vrork  should  be  of  high  carat  and  of  as  great 
tensile  strength  and  rigidity  as  possible.  It  should  not  be  overheated. 
Coin  gold  seems  to  be  well  adapted  for  this  purpose,  as  it  possesses  the 
qualities  above  mentioned  and  gives  a  good  sharp  casting. 

All  Porcelain  Crown  With  Cast  Base. — ^This,  being  one  of  the  simplest 
and  easiest  crowns  to  make,  will  be  first  considered.  The  root  for  a 
crown  of  this  kind  requires  little  preparation,  as  compared  with  one  for 
a  Richmond  or  other  banded  crown.  The  face  of  the  root  may  be  irregu- 
lar from  decay  or  fracture,  or  it  may  have  been  ground  down  to  meet  the 
requirements  of  the  case.  In  any  event,  it  should  be  cut  well  beneath  the 
gum  line  on  the  labial  side,  and  on  the  lingual  side  enough  to  suit  the 
requirements  of  articulation.  The  lingual  side  should,  if  it  is  possible, 
be  beveled  so  that  the  base  will  overlap,  thus  gi"ving  additional  support 
to  the  crown,  and  at  the  same  time,  serving  to  strengthen  the  root  and 
overcome  the  liability  of  fracture.  (Fig.  704.)  The  crown  is  then 
ground  to  conform  to  the  size  and  shape  of  the  root,  and  to  touch  it  only 
at  the  labial  side,  lea^^ng  plenty  of  room  between  the  balance  of  the 
face  of  the  root  and  the  crown  to  allow  of  a  heavy  base,  as  in  Fig.  705. 

The  dowel,  or  pin,  which  is  preferably  made  of  iridio-platinum  or 
platinized  gold  wire,  is  then  adjusted  and  should  be  of  sufficient  length  to 
go  nearly  or  quite  to  the  bottom  of  the  hole  in  the  base  of  the  crown  and 


716  ARTIFICIAL   CROWNS. 

into  the  root  to  a  depth  at  least  equal  to  the  length  of  the  crown.  (Fig. 
705.)  It  is  well  to  fiow  a  little  sticky  wax  around  the  post,  between  the 
base  of  the  crown  and  the  face  of  the  root,  at  point  a  in  Fig.  705,  as  the 
wax,  of  which  the  base  is  to  be  made,  will  adhere  to  the  post  l)etter  than 
it  would  otherwise. 

The  base  of  the  crown  is  then  lightly  oiled,  or  coated  very  thinly  with 
cocoa-butter  to  prevent  the  wax  from  sticking,  and  the  base  wax,  which 
should  be  a  little  softer  and  tougher  than  the  ordinary  inlay  wax,  is  soft- 
ened and  pressed  around  tli(.'  i)in  at  the  base  of  the  crown,  which  is  then 
forced  on  the  root  and  carefully  adjusted  in  position.  After  the  wax 
has  been  chilled,  the  surplus  is  carefully  trimmed  away,  until  it  is  perfectly 
smooth  and  flush  with  the  sides  of  the  crown  and  root.  (Fig.  700.)  The 
crown,  together  with  the  pin,  is  then  removed  from  the  root  and  the 
sprue  wire  attached,  as  in  Fig.  706,  by  heating  it  just  enough  to  imbed  it 
slightly  in  the  wax.  It  may  be  more  firmly  fixed  by  flowing  a  very  small 
amount  of  wax  around  it  at  the  point  of  entrance,  after  which  the  crown 
is  removed. 

The  sprue  wire  is  now  placed  in  the  base  of  the  flask  (Fig.  707),  and 
the  crown  base  is  invested  in  the  same  maimer  as  an  inlay,  painting  the 


Fig.  705  Fi«-  700 


investment  very  carefully  so  that  there  may  be  no  air  bubbles,  which 
would  be  reproduced  in  gold  in  the  casting  and  interfere  with  the  fit  of 
the  base.  After  casting,  it  is  cleaned  and  polished  and  adjusted  to  the 
crown  and  root.  The  base  is  first  cemented  to  the  crown,  and  after  the 
cement  has  thoroughly  hardened  it  is  cemented  in  the  mouth. 

This  makes  a  lasting  crown  when  used  singly,  but  it  is  not  to  be  used 
for  a  bridge,  as  all  bridge  abutments  should  be  banded. 

Banded  Crowns. — The  caps  for  these  crown  can  be  made  in  the  same 
way  as  for  a  Richmond  crown,  being  carried  well  beneath  the  gum 
labially.  The  impression  is  taken  and  the  model  prepared  in  the  usual 
way. 

The  crown  is  ground  in  the  same  manner,  as  already  described  in 
treating  of  the  crown  with  the  cast  base,  being  beveled  lingually  and 
mesially  and  distally  about  half  way  to  the  labial  face.  (Fig.  708.) 
This  allows  a  sort  of  a  socket  for  the  crown  to  set  in  and,  at  the  same 
time,  insures  the  correct  position  of  the  crown  on  the  base. 

The  base  of  the  crown  is  lubricated,  so  that  the  wax  will  not  stick  to  it, 
and  the  wax  is  flowed  in  between  the  crown  and  the  cap,  until  it  is  well 


THE  CASTING  PROCESS  IN  CROWN    WORK. 


717 


filled,  after  which  it  is  carved  flush  with  the  crown  and  the  band  and  the 
sprue  wire  attached,  as  in  Fig.  706.  The  crown  is  now  removed,  leaving 
a  wax  base  attached  to  the  cap.  It  is  then  set  in  the  flask  base  and  in- 
vested and  cast  in  the  usual  manner.  The  base  should  be  polished  with 
the  crown  in  position,  after  which  the  crown  is  cemented  to  the  base  and 
kept  under  pressure  until  the  cement  has  hardened.  It  is  then  ready  for 
the  mouth. 

This  method  of  procedure  may  be  followed  in  making  any  crown  of  this 
type  from  molars  to  incisors. 

Crown  With  Porcelain  Facings. — In  crowns  of  the  Richmond  type,  where 
a  porcelain  facing  is  used,  the  cap  and  pin  are  made  and  fitted  to  the 


Fig.  708 


Fig.  709 


Fig.   710 


Fig.  711 


root,  and  the  facing  ground  to  place,  sloping  it  slightly  more  than  the 
floor,  so  as  to  allow  the  gold  to  flow  under  the  facing.  (Fig.  709.)  If 
there  has  been  much  recession  of  the  gum,  so  that  the  band  has  to  be 
sloped  greatly,  labially  (Fig.  710),  it  is  well  to  grind  a  step  in  the  bottom 
of  the  facing,  so  that  there  may  be  a  good  base  for  it  to  rest  on,  thus 
rendering  it  less  liable  to  be  forced  down  the  incline  and  fractured. 
(Fig.  710.)  The  facing  is  then  lubricated  on  the  hngual  side,  and  held 
in  place  with  a  little  sticky  wax  on  the  labial  side,  or  a  light  wall  of 


Fig.  712 


Fig.  713 


Fig.  714 


"^ 


plaster  or  modelling  composition,  and  the  lingual  side  is  built  up  with 
hard  inlay  wax  and  carved  and  smoothed  carefully.     (Fig.  711.) 

It  should  be  remembered  that  the  better  it  is  finished  in  the  wax,  the 
easier  it  will  be  to  finish  the  completed  crown.  The  sprue  wire  is  at- 
tached, as  shown  in  Fig.  711,  the  facing  carefully  removed  and  small  pins 
of  graphite  inserted  in  the  holes  left  by  the  tooth-pins,  leaving  them  long 
so  as  to  be  gripped  in  the  investment.  (Fig.  712.)  Another  way  is  to 
enlarge  the  pin-holes  in  the  wax  after  removing  the  facings  and  dovetail 
them  on  the  inside,  as  in  Fig.  713.  This  x?an  be  easily  done  \^^th  a  small 
coarse  bur.     It  is  then  invested,  care  being  taken  to  fill  the  pin-holes,  if 


718  ARTIFICIAL   CROWNS. 

they  have  been  enlarged,  and  cast.  After  the  casting  has  l)een  made,  the 
graphite  pins  are  removed,  the  sides  of  the  holes  roughened,  and  the 
piece  cleansed  and  polished.  The  tooth-pins  are  then  lightly  threaded 
or  roughened  and  the  facing  cemented. 

If  the  holes  were  enlarged  and  dovetailed,  the  pins  may  be  flattened 
a  little  and  then  bent  at  right  angles,  as  shown  in  Fig.  714,  and  cemented 
in  place. 

Casting  Directly  on  the  Facings. — In  making  a  single  crown  or  a  small 
bridge,  where  it  is  intended  to  cast  directly  against  the  facings,  great 
care  must  be  used  that  the  wax  does  not  overlap  the  porcelain  at  any 
point.  This  is  of  the  utmost  importance,  as  if  the  wax  is  extended  so  as 
to  grip  the  facings,  the  contraction  of  the  metal  on  cooling  will  be  certain 
to  crush  them.  The  wax  should  be  carefully  trimmed  to  the  edges  of  the 
porcelain,  and  it  is  a  good  plan  to  clean  them  well  by  rubbing  the  edges 
with  a  piece  of  tape  or  cloth  before  investing. 

Drying  Out  and  Heating  Up  the  Flask.— The  flask  should  be  dried  out 
carefully  and  then  brought  to  a  very  high  heat  throughout  so  that  the 
facing  will  be  red  hot  when  the  gold  comes  in  contact  with  it.  If  the 
facing  is  cold,  or  but  slightly  heated,  when  the  casting  takes  place,  the 
rapid  expansion  of  the  platinum  pins,  taking  the  heat  so  much  more 
quickly  than  does  the  porcelain,  would  fracture  the  facing.  After  cast- 
ing, the  flask  should  be  allowed  to  become  perfectly  cold  before  opening, 
after  which  the  piece  is  cleansed  and  is  ready  for  finishing. 

The  crown,  or  the  bridge,  which  has  been  made  in  this  way  will  be 
satisfactory,  providing  there  is  little  or  no  strain  on  the  facings,  but  unless 
this  is  the  case  the  method  is  decidedly  objectionable. 

In  a  facing  which  is  reheated,  in  soldering  or  otherwise,  the  strength 
of  the  porcelain  is  diminished,  and  especially  is  this  so  if  a  mass  of  gold  is 
forced  upon  it  in  a  molten  state.  The  piece  may  come  out  with  the  fac- 
ings seemingly  intact,  but  they  have  been  weakened  and  in  the  majority 
of  cases,  if  examined  under  a  microscope,  will  show  innumerable  fine 
checks  running  all  through  them.  It  is  far  better  not  to  subject  the 
facings  to  this  refiring,  if  it  is  possible  to  avoid  it,  as  they  are  thereby 
rendered  much  more  serviceable  than  they  would  be  otherwise. 

REPAIRING    OF    CROWNS. 

When  from  any  cause  it  is  found  necessary  to  remove  a  full  gold 
crown  from  a  tooth,  if  the  crown  has  been  properly  fitted  and  cemented, 
it  will  generally  be  necessary  to  cut  the  band  in  order  to  get  it  off.  This 
may  be  easily  done  with  one  of  the  crown  slitters  which  are  made  for 
this  purpose,  as  illustrated  in  Fig.  715.  With  one  beak  resting  on  the 
cusp  and  the  other  caught  under  the  edge  of  the  crown  the  forceps  are 
closed,  dividing  the  band  all  of  the  way  to  the  cusp,  when  by  giving  a 
slight  rocking  movement,  the  crown  may  generally  be  easily  lifted 
off.  Should  this  not  be  the  case,  an  instrument  is  passed  under  the  flap 
and  worked  around  the  tooth  to  ^emo^•e  the  cement  and  the  band  grad- 
ually loosened.  A  hatchet-shaped  excavator  can  be  used  to  do  the 
cutting,  the  blade  being  drawn  from  the  cervical  edge  to  the  cusp,  until 


REPAIRING  OF  CROWNS. 


719 


the  band  is  divided.     A  small  wheel  bur  will  do 
the  cervix  to  the  cusp  in  the  same  way  as  with 

In  repairing  the  crown,  the  cem- 
ent is  thoroughly  removed  and  the 
edges  of  the  break  brought  into  close 
contact  and  soldered.  If  there  is 
much  loss  of  material  at  the  site  of 
the  cut,  a  narrow  strip  of  thin  plati- 
num or  of  pure  gold  is  waxed  over 
the  line  of  division  on  the  inner  side 
of  the  cap,  which  is  then  filled  with 
investing  material  and  the  broken 
edges  united  with  solder. 

The  repairing  of  a  porcelain  faced 
crown  is  a  much  more  difficult  oper- 
ation. If  the  crown  has  been  set 
with  gutta-percha,  it  may  be  easily 
removed  by  grasping  it  with  a  heated 
pair  of  pliers  or  forceps,  having 
first  protected  the  lips  and  gums  of 
the  patient  with  napkins.  If  it  has 
been  set  with  oxyphosphate  of  zinc 
much  more  trouble  will  be  experi- 
enced in  getting  it  off.  It  will  be 
necessary  first  to  separate  the  cap 
from  the  pin.  This  may  be  done 
by  passing  a  drill  from  the  lingual 
side  through  the  base  of  the  back- 
ing and  the  floor  of  the  cap  to  one  side 
of  the  pin  and  then  cutting  the  pin 
through  with  a  very  small  fissure  bur, 
after  which  the  cap  is  easily  pried  off. 
To  remove  the  post,  the  cement 
must  be  cut  away  from  around  it 
until  it  has  become  loosened.  A 
very  fine  spear-pointed  drill  will  do 
this  best.  The  shank  of  one  of  the 
finest  burs  or  af  a  Gates-Glidden 
drill,  flattened  on  two  sides  and  then 
ground  to  a  spear  point  makes  an 
excellent  drill  for  this  work,  being 
smaller  than  any  obtainable  at  the 
dental  depots.  The  cement  is 
drilled  away  close  to  the  pin  all 
around,  inclining  the  drill  toward 
the  post  at  all  times  so  as  to  weaken 
the  root  as  little  as  possible  by  cut- 
ting into  it.     From  time  to  time  an 


the  work,  cutting  from 
an  excavator. 

Fig. 713 


^siaiiC/' 


720  ARTIFICIAL  CROWXS. 

effort  may  be  made  to  loosen  tlie  pin  by  grasping  it  with  a  pair  o^ 
strong  small  nosed  pliers  and  trying  to  rotate  it.  If  it  will  not 
loosen,  the  drilling  is  to  be  carried  deeper  until  it  can  be  removed. 
The  remainder  of  the  cement  is  then  removed  from  the  canal  and 
a  new  pin  fitted  to  it.  The  palatal  portion  of  the  crown  with  the 
backing  is  then  cut  away  (Fig.  710),  the  cap  placed  on  the  root  and 
the  pin  waxed  in  place.  The  cap  and  pin  are  now  removed,  invested 
and  soldered,  after  which  the  facing  is  ground,  backed  and  the  crown 
soldered. 

There  are  several  ways  of  replacing  a  facing  in  the  mouth  without 
removing  the  cap  and  pin  from  the  root.  A  good  way  to  do  this  where 
the  remaining  metal  portion  of  the  crown  has  sufficient  thickness,  is 

Fig.  710  Fic.  717  Fic.  718  Fig.  719  Fig.  720 


as  follows:  the  remnants  of  the  pins  are  first  cut  off  and  ground  flush 
with  the  backing  and  an  impression  taken  covering  the  backing  and 
floor  of  the  cap,  and  a  cast  made  of  plaster,  cement  or  Spence  metal.  A 
hole  is  then  cut  in  the  back  of  the  cast  large  enough  for  the  pins  to  enter 
freely.  (Fig.  717.)  The  facing  is  then  selected  and  ground  to  fit  the 
cast  accurately.  The  backing  of  the  crown  in  the  mouth  is  then  cut 
out  to  accommodate  the  pins,  care  being  used  not  to  come  through  on 
the  lingual  side.  The  cavity  is  then  deeply  undercut  all  around,  mak- 
ing it  strongly  retentive  in  shape.  (Figs.  718  and  719.)  The  pins  of 
the  facing  are  then  flattened  at  the  ends  and  bent  at  right  angles,  one 

Fig.  721  Fig.  722  Fig.  723  Fig.  724 


being  cut  off  so  that  it  is  a  little  shorter  than  the  other  so  that  when  the 
long  pin  is  inserted  and  the  facing  pressed  as  far  to  that  side  as  it  will 
go,  the  short  pin  will  just  pass  through  the  opening  in  the  backing. 
(Fig.  720.)  The  cavity  is  now  filled  with  cement  and  the  backing  and 
floor  covered.  The  long  pin  is  first  introduced,  the  facing  carried  to 
that  side  until  the  shorter  one  will  enter.  It  is  now  pressed  tightly  in 
place  and  then  forced  back  until  the  sides  of  the  facing  are  even  with 
the  backing.  Tliis  will  bring  the  ends  of  both  the  short  and  long  pins 
under  the  ledge  of  the  cavity  and  when  the  cement  has  hardened,  it  will 
be  impossible  to  remove  the  facing  except  by  breaking  it.  (Fig.  721.) 
Another  method  of  repair  in  the  mouth  is  by  riveting  a  facing.  It 
should  first  be  fitted  to  a  cast  as  described  and  a  backing  of  tin  foil  or 


RETAIXIXG  MEDIA.  721 

paper  fitted  to  it  and  trimmed  carefully  to  the  edge  of  the  facing  all 
around.  This  backing  is  then  removed  and  placed  in  position  over  the 
gold  backing  of  the  crown  in  the  mouth,  (Fig.  722.)  The  holes  in 
the  backing  will  now  show  the  exact  position  of  the  pins  of  the  facing, 
and  the  holes  may  be  drilled  with  a  small  spear-pointed  drill  the  exact 
size  of  the  pin.  The  holes  are  then  countersunk  from  the  palatal  side 
and  the  pins  cut  off  so  that  they  will  project  only  a  slight  distance 
through  the  backing.  (Fig.  723.)  The  riveting  is  done  with  a  plate 
punch.  The  facing  is  removed  and  the  backing  and  floor  of  the  cap 
covered  with  cement  of  about  the  same  consistence  as  that  used  in  set- 
ting a  crown.  A  piece  of  lead  or  a  thickly  folded  napkin  is  placed  over 
the  facing  with  the  die  side  of  the  punch  resting  on  this,  and  while  the 
cement  is  yet  soft,  the  pin  is  riveted  by  rubbing  and  burnisliing  with  the 
punch  end  of  the  forceps  until  the  countersink  is  entirely  filled.  (Fig. 
724.)  After  riveting,  any  excess  platinum  of  the  pin  may  be  ground 
away  and  the  back  polished.  If  a  facing  is  carefully  riveted,  the  holes 
not  being  too  large,  as  strong  a  repair  as  can  be  made  by  any  method 
is  obtained.  If  the  cement  has  been  allowed  to  harden  before  the 
riveting  is  done  it  will  be  broken  and  crumble  away. 

Dr.  Emory  A.  Bryant^  describes  a  novel  method  of  attaching  a  new 
facing.  A  tap  and  die  the  size  of  the  tooth  pins  are  necessary,  together 
with  a  special  countersinking  tool  and  a  screw-driver.  The  pins  are 
cut  from  the  old  backing  and  holes  are  drilled  the  size  of  the  pins  of  the 
new  facing,  and  in  the  proper  positions.  With  the  countersinking  tool 
held  in  a  right  angle  hand  piece,  the  holes  are  countersunk  exactly  to 
the  outer  wall  of  the  backing.  The  nuts  are  made  the  size  of  the  coun- 
tersink. By  means  of  the  oiled  die,  a  thread  is  cut  on  each  pin  of  the 
tooth,  and  continued  to  the  back  of  the  facing,  exercising  great  care 
that  the  pins  are  not  twisted.  The  facing  is  set  in  position  and  each 
nut  is  loosely  adjusted,  then  alternately  screwed  into  place,  drawing 
the  facing  close  to  the  backing.  The  protruding  portions  of  nuts  and 
pins  are  then  ground  down  and  polished. 

This  method  of  replacing  broken  facings  is  very  ingenious,  but  it  is 
a  question  whether  the  cutting  of  a  thread  on  such  a  small  pin,  will 
not  weaken  it  to  such  an  extent  as  to  render  it  of  little  value  where  much 
strength  is  required.  It  is  better  if  the  full  strength  of  the  pin  can  be 
preserved. 

RETAINING  MEDIA. 

The  two  materials  commonly  used  as  retentive  media  for  artificial 
crowns  are  gutta-percha  and  the  phosphate  of  zinc. 

Each  of  these  substances  possesses  properties  which  govern  their  em- 
ployment. Oxy phosphate  is  adhesive,  extremely  hard,  therefore,  diffi- 
cult of  removal,  and  is  more  or  less  soluble  in  the  fluids  of  the  mouth. 
The  greater  the  amount  of  acid  present  in  the  saliva,  the  greater  the 

/  The  Dental  Cosmos.  Vol.  xxxvi.,  p.  469,  et  seq. 
46 


722  ARTIFICIAL  CROWNS. 

solubility  of  the  cement.  It  disintegrates  most  (juickly  at  the  cervical 
margin,  where  acid  formations  are  in  greatest  amount,  and  is  somewhat 
porous.  Protected  from  contact  with  the  oral  fluids,  it  lasts  indefinitely. 

Gutta-percha  is  almost  unchangeable  in  the  mouth,  is  plastic,  is 
softer  than  zinc  phosphate,  and  loses  substance  by  attrition.  It  may  be 
resoftened  by  heat,  but  softening  becomes  more  difficult  with  age. 

Therefore,  zinc  phosphate  is  selected  for  the  retentive  medium  when 
it  is  protected  from  the  fluids  of  the  mouth,  where  such  space  exists  as 
demands  more  rigidity  than  could  be  furnished  by  a  mass  of  gutta- 
percha, and  where  adhesiveness  is  a  desideratum,  where  support  is  to 
be  furnished  for  a  metal  surface  susceptible  to  change  of  shape,  as,  for 
instance,  in  a  thin  gold  crown,  where  gutta-percha,  if  used,  would  by  its 
elasticity  permit  change  of  shape  in  the  band. 

Gutta-percha  is  to  be  employed  where  the  fluids  of  the  mouth  have 
access,  where  such  a  thin  layer  of  retentive  medium  is  required  that  its 
pHal)ility  does  not  affect  its  fixation,  or  where  it  may  be  desirable  to 
furnish  means  for  removal  of  a  crown  should  this  ^ver  become  necessary. 

Thus  in  all  crowns  supported  by  bands  or  barrels  which  extend 
beneath  the  edge  of  the  gum,  zinc  phosphate  is  the  proper  retaining 
medium. 

Also  in  cases  where  a  large  space  exists  between  crown  and  root; 
that  is,  an  interior  space  not  marginal,  for  marginal  adaptation  in  all 
crowns  must  be  perfect. 

In  those  crowns  which  are  placed  upon  posts  which  have  been  fixed 
in  roots  to  serve  as  supports  to  porcelain  crowns  or  faces,  the  retentive 
medium  becomes  practically  part  of  the  crown. 


SETTING  CROWNS  WITH  ZINC  PHOSPHATE. 

The  zinc  phosphate  employed  in  the  setting  of  crowns  should  possess 
the  characteristics  which  would  recommend  the  specimens  to  be  used  as 
filling  material.  It  should,  however,  flow  freely,  and,  as  the  difficulty 
of  maintaining  dryness  is  increased,  it  should  set  promptly  ami  yet 
with  sufficient  deliberation  to  permit  the  accurate  adaptation  of  the 
crowns.  The  operator  should  by  actual  test  determine  precisely  the 
peculiarities  of  the  particular  cement  he  is  to  employ.  Specimens  of 
zinc  phosphate  differ  so  markedly  in  their  behavior  that  it  is  always 
wise  to  make  preliminary  tests  of  each  package. 

It  is  advisable  to  set  all  pin  crowns  so  that  they  can  be  removed  with- 
out mutilating  them,  if  at  some  future  time  it  should  be  desirable  to  do 
so  for  the  purpose  of  repairing  them,  or  in  case  they  should  be  needed 
as  anchorages  for  a  bridge.  An  excellent  method  of  setting  them  so 
that  they  will  be  perfectly  rigid  and  at  the  same  time  render  them  easily 
detachable,  is  first  to  give  the  pin  and  the  inside  of  the  cap  and  band  a 
coating  of  chlora-percha.  A  solution  may  not  always  be  at  hand,  and  a 
convenient  way  to  do  this  is  to  take  a  fine  camel's  hair  brush,  dip  it  in 
chloroform  and  then  rub  it  on  base-plate  gutta-percha  and  paint  the 


RET  A  rX  IXC  MEDIA. 


723 


cap  and  pin  The  solution  will  drv  very  quickly  and  the  crown  is  then 
set  with  oxyphosphate  of  zinc.  If  at  any  time  it  is  desired  to  remove 
the  crown  it  can  be  easily  done  with  a  pair  of  heated  forceps  or  pliers. 
The  Critenden  cement  syringe  (Fig.  725)  is  a  most  useful  aid  in  ce- 
menting crowns  or  bridges,  especially  where  several  pin  crowns,  either 
single  or  as  abutment  pieces  are  to  be  set  at  one  time.  It  consists  of  a 
nickle  plated  brass  cylinder,  with  the  needle  or  tube  small  enough  to 
enter  the  enlarged  canal,  and  a  brass  plunger.     There  is  an  opening  in 

Fig.    725 


the  side  of  the  cylinder  for  the  introduction  of  the  cement.  The  root 
is  thoroughly  dried  and  the  cement  mixed  to  the  consistence  of  thick 
cream  and  placed  in  the  cylinder.  The  piston  is  then  put  in  and  the 
end  of  the  needle  carried  to  the  end  of  the  canal  and  the  cement  forced 
into  it,  -u-ithdra^-ing  the  needle  slowly  at  the  same  time.  In  this  way, 
the  apical  extremity  of  the  canal  is  filled  first  and  any  air  which  may  be 
in  it  is  forced  out.  A  number  of  roots  may  be  filled  in  this  way  in  a  few 

Fig.    726 


seconds  and  there  will  be  ample  time  to  put  the  crowns  or  bridge  in 
place  before  the  cement  has  set. 

As  soon  as  the  piece  is  in  place,  the  syringe  is  plunged  into  a  basin  of 
cold  water  and  the  piston  worked  back  and  forth  to  free  it  from  the 
remaining  cement  while  this  is  still  soft.  If  the  cement  is  too  hard  to  be 
forced  out  it  may  be  removed  with  the  drill  which  comes  for  this  pur- 
pose. 

When  gutta-percha  is  to  be  employed,  it  is  necessary  that  the  several 
parts  shall  be  at  a  temperature  which  will  permit  the  ready,  deliberate 
and  accurate  adjustment  of  the  crown  and  gutta-percha  to  the  root. 

A  satisfactory  method  of  manipulation  is  as  follows:    a  napkin  is 


724  ARTIFICIAL  CROWNS. 

adjusted  so  that  the  root  is  protected  from  moisture;  the  canal  is  wiped 
out  with  caustic  pyrozone. 

The  crown  is  laid  upon  a  gutta-percha  heater  (Dr.  How's  steatite 
slab  is  useful  for  this  purpose),  a  piece  of  tough  gutta-percha  is  laid  be- 
side the  crown,  and  when  soft  is  pressed  out  between  the  fingers  into  a 
sheet,  which  is  wrapped  around  the  heated  post.  The  root-canal  is 
wiped  out  with  oil  of  cloves  or  water  so  that  gutta-percha  will  not  ad- 
here to  it,  and  the  heated  crown  and  softened  gutta-percha  are  pressed 
into  position.  If  an  excess  of  gutta-percha  has  l)een  applied,  the  sur- 
plus will  be  squeezed  from  beneath  the  outline  of  the  crown.  This 
excess  is  to  be  trimmed  away  by  means  of  sharp  scissors.  If  there  has 
not  been  sufficient  gutta-percha  attached  to  the  post,  more  is  to  be 
added  to  that  on  the  post  and  the  crown  reapplied,  and  then  the  excess 
trimmed  off.  The  crown  is  returned  to  the  heater,  which  is  ajjain  held 
over  the  flame  until  the  fusible  metal  melts.  A  fresh  napkin  is  placed 
in  position;  the  root  is  wiped  out  with  alcohol  and  dried  by  means  of  a 
hot  blast.  It  is  then  wiped  out  with  one  of  the  essential  oils.  A  small 
sheet  of  softened  gutta-percha  is  added  about  the  post,  and  when  the 
crown  and  gutta-percha  are  thoroughly  heated,  the  crown  is  seized  be- 
tween the  fingers,  protected  by  a  napkin,  and  pressed  into  position.  A 
heated  crown  adjuster  is  now  applied  to  the  crown,  and  it  is  forced  into 
position;  the  excess  of  gutti-percha  is  squeezed  out  at  the  margins  of 
the  crown. 


CHAPTER    XVII. 

AN  ASSEMBLAGE  OF  UNFILED  CROWNS  (BRIDGE-WORK). 
By  H.  H.  Burchard,  M.D.,  D.D.S.  and  F.  A.  Peeso,  D.D.S. 

A  DENTAL  bridge  is  essentially  a  continuous  masticating  surface 
anchored  to  supporting  abutments  at  two  or  more  points  of  its  length, 
the  fixation  and  retention  of  the  device  depending  upon  anchorage  on 
or  in  the  natural  teeth;  any  support  derived  through  contact  of  the 
appliance  with  the  natural  gum  is  purely  secondary.  The  method  and 
variety  of  support  are  the  direct  reverse  of  those  of  an  artificial  denture 
mounted  upon  a  plate,  for  here  the  primary  support  is  by  the  natural 
gum,  and  any  further  support  derived  through  attachment  to  the  nat- 
ural teeth  is  merely  adjunctive.  The  term  "removable  bridge"  is 
gradually  being  extended  to  include  devices  which  receive  their  support 
both  from  the  membrane  and  from  the  teeth  or  roots. 

The  appliances  in  contemporary  use  which  are  included  under  the 
head  of  "dental  bridges"  comprise  a  multitude  of  defaces,  the  con- 
struction and  support  of  which  depend  upon  a  few  principles.  The 
many  different  forms  are  modifications  of  a  limited  number  of  types, 
the  differences  between  many  of  apparently  diverse  types  being  merely 
technical  and  not  those  of  mechanical  principles. 

The  natural  teeth  or  roots  supporting  the  bridge  are  called  its  "abut- 
ments," the  crowns  placed  over  them  or  the  bars  anchored  in  them,  the 
"abutment  pieces."  The  intervening  portions  of  the  fixture  are  known 
as  "the  body  of  the  bridge,"  and  the  several  pieces  of  which  it  is  com- 
posed, "the  dummies." 

History. — Devices  which  might  be  classed  as  dental  bridges  are 
probably  as  old  as  the  earliest  attempts  at  dental  prosthesis.  The  plac- 
ing of  a  band  of  metal  about  one  natural  tooth  is  the  simplest  means  for 
supporting  an  additional  tooth,  and  probably  the  first  attempted. 

Ajnong  the  archcieological  remains  of  the  Etruscan  life  are  found  de- 
vices which  bear  a  family  resemblance  to  bridge-work. 

The  present  varieties  included  in  the  generic  name  of  dental  bridges 
are  the  evolution  of  processes  and  type  suggested  and  made  early  in 
this  century.  As  an  example  of  an  early  device  bearing  a  close  resem- 
blance to  a  contemporary  appliance,  Dr.  W.  F.  Litch  ^  gives  a  cut  from 
the  work  of  F.  jNIaury  (1S28),  showing  six  anterior  teeth  anchored  in 
the  roots  of  the  canines  by  means  of  two  posts  placed  in  the  enlarged 
pulp-canals. 

'  American  Svstem  of  Dentistrs'  vol.  ii.,   Fig  758. 

725 


■26 


AX  ASSEMBLAGE  OF  VXITEI)  CROWXS. 


Ill  April,  1835,  Dr.  Win.  II.  Dwindle  NlcscrilH'd  the  profj^enilor  of 
the  inoderii  pin  and  plate  bridge,  together  with  the  prototype  of  another 

form  of  bridge  in  present  use:  "After  the  root  is  filled  with  gold 

and  properly  finished,  an  impression  of  its  surface  is  taken  in  wax,  from 
which  castings  are  made,  and  from  these  plates  are  swaged.  These  are 
adjusted  to  the  tooth  and  a  gold  pivot  soldered  to  the  upper  surface. 
A  plate  tooth  is  now  skilfully  adapted  to  the  fixture,  when  it  is  ready 
for  use.  In  this  way  a  plate  may  be  carried  across  an  intervening  space 
unoccupied  by  roots,  and  an  unbroken  row  of  teeth  mounted  upon  it." 
In  January,  1S71,  Dr.  Benj.  J.  Bing  applied  for  a  patent  for  a  bridge 
devic  to  be  anchored  Ijy  wire  extremities  into  cavities  in  the  natural 
teeth. 

A  form  of  removable  bridge  was  introduced  by  Dr.  W.  G.  A.  Bonwill 
in  1873  (Fig.  727). 

The  revival  of  bridge  work,  or  the  modern  ideas  of  these  forms  of 
appliance,  arose  with  the  advent  of  the  barrel  and  collar  crowns.     This 

variety  of  crown  made  and  applied  early  in 
the  century,  appears  to  have  had  very  lim- 
ited em})loyment  until  its  elaboration  by 
Dr.  C.  ]M.  Richmond.  The  primary  prin- 
ciple involved  was,  as  stated,  known  and 
applied  for  many  years;  it  is  but  thirty 
years,  however,  since  the  general  adoption 
of  the  idea. 

In  its  simplest  form  a  dental  bridge  con- 
sists of  two  or  more  crowns  bearing  between, 
\  •  and  rigidly  attached  to  them,  substitutes 

for   the  crowns  of  the  intervening  natural 
teeth  which  have  been  lost.     The  primary 
object  sought  has  been  disuse  of  a  plate,  and  such  firmness  and  immo- 
bility as  would  furnish  a  better  means  in  mastication  than  is  possible 
with  a  plate  denture. 


Fi(^.  727 


CLASSIFICATION  OF  BRIDGES. 

Dental  bridges  may  be  divided  into  two  primary  classes — fixed  or 
removable. 

Fixed  bridges  are  those  which  are  so  attachefl  to  the  abutments  that 
removal  of  a  properly  fitted  and  adjusted  piece  is  not  practicable  with- 
out more  or  less  mutilation  of  the  abutment  crowns  (Fig.  728  ). 

Removable  bridges  are  those  the  supporting  crowns  of  which  may 
be  detached  from  the  abutments  without  disturbing  the  integrity  of  the 
appliance. 

Class  1  may  be  subdivided  into  sub-classes  according  to  the  method 
and  means  of  anchorage: 


^  American  Journal  (jf  Dental  Science 


CLASSIFICATIOX  OF  BRIDGES.  727 

Sub-class  1 :  Those  attached  to  the  abutments  by  means  of  collar 
or  barrel  crowns  (Fig,  728  ). 

Sub-class  2:  Those  in  which  fixation  is  secured  by  means  of  metallic 
bars  anchored  in  the  crowns  or  roots  of  teeth. 

The  features  of  both  sub-classes  may  be  combined  in  one  piece,  a 
bar  anchorage  at  one  extremity  and  a  collar  or  barrel  crown  at  the 
other  (Fig.  729  ).  Devices  of  the  varieties  of  Dr.  Litch's  pin  and  plate 
bridge  belong  to  sub-class  2;  the  open-cylinder  partial  crown  terminals 
to  sub-class  1. 

The  usual  forms  of  removable  bridges  have  abutment  crowns  made 
of  cylinders,  which  telescope  over  metallic  ferrules  which  have  been  per- 
manently attached  to  the  abutments.  This  form  of  bridge  was  devised 
to  facilitate  removal  when  repair  of  the  piece  became  necessary;  to  per- 
mit of  occasional  removal,  so  that  the  bridge  might  be  perfectly  cleansed; 
to  furnish  a  method  of  attachment  when  the  abutment  teeth  were  in 
such  malposition  that  a  fixed  bridge  could  not  be  attached  without  un- 
due mutilation  of  natural  crowns. 

Fig.  728 


The  introduction  of  the  removable  bridges  has  negatived  several  of 
the  objections  urged  against  the  practice  of  this  work.  First,  the  want 
of  perfect  cleanliness,  since  removable  bridges  may  be  detached  when 
necessary  and  receive  a  perfect  cleansing.  In  case  of  repair  being  neces- 
sary^  the  piece  may  be  removed  without  mutilation  of  the  abutment 
crowns.  It  furnishes  a  means  for  bridging  spaces  enclosed  by  over- 
hanging teeth.  These  bridges  possess  so  many  advantages  over  the 
fixed  variety  that  it  is  probable  they  will  largely  supersede  the  latter. 

A  type  of  device  somewhat  resembling  a  bridge  has  been  constructed 
and  described,  which  combines  some  of  the  features  of  both  bridge  and 
plate.  Extending  from  the  terminal  abutment  pieces  of  a  fixed  bridge 
are  arms  or  wings  resting  upon  the  gum  and  supporting  one  or  more 
artificial  teeth  on  each  of  them.  The  mechanical  principle  involved 
in  this  device  is  faulty.  The  plate  pieces  to  furnish  any  material 
support  must  be  of  such  size  as  to  render  the  appliance  highly 
objectionable  hygienically;  and  if  too  small  to  serve  as  effective  aux- 
iliary supports,  the  abutments  are  overstrained. 

In  judging  of  the  merits  and  demerits  of  this  phase  of  prosthesis,  it 


728  AX  ASSEMBLAGE  OF   VXITEI)  CROWNS. 

would  Ik*  manifestly  improper  to  acee])t  all  the  claims  of  llie  enthusias- 
tic advocates,  or  to  be  governed  hy  the  oj)iiiions  of  its  pronounced 
opponents. 

The  advantages  claimed  for  bridge-work  are  the  removal  of  many  of 
the  deficiencies  associated  with  plate  dentures.  First,  the  bridge  is  im- 
movable; second,  there  is  no  interference  with  articulation;  third,  teeth 
may  be  replaced  without  the  necessity  of  wearing  a  cumbrous  plate. 
The  several  advantages  enumerated  by  advocates  may  be  all  summed 
up  under  these  three  headings. 

The  objections  urged  against  bridge-work  in  the  past  have  l)een  in 
great  measure  removed;  others  remain.  It  does  not  restore  lost  gum 
contour,  except  wuth  those  devices  known  as  plate  bridges.  It  is  un- 
cleanly; the  space  existing  between  portions  of  the  V>ridge  surface  and 
the  natural  gum  are  fre(juently  inaccessible  to  the  tooth-brush  and  con- 
tain decomposing  food  debris.  Teeth  are  often  necessarily  mutilated 
to  serve  as  correct  abutments,  and  some  operators  advocate  the  de\dtal- 
ization  of  the  pulps  of  the  teeth  thus  prepared  for  abutment,  on  the 
ground  that  their  mutilation  and  the  fact  that  they  may  be  subjected 
to  a  greater  mechanical  stress  than  they  can  safely  bear,  is  liable  to  cause 
the  death  of  their  pulps  with  the  phenomena  which  usually  accompan- 
ies such  a  result,  and  which  would  be  more  difficult  to  relieve  and  treat 
after  the  bridge  was  permanently  fixed. 

The  intrinsic  merit  of  properly  constructed  bridge-work  is  undoubted. 
Many  of  the  objections  stated  above  do  not  attach  to  properly  designed 
and  constructed  pieces;  they  are  based  upon  such  practice  of  bridge- 
work  as  is  now  regarded  as  unjustifiable. 

It  is  to  be  recognized  that  neither  bridge-nor  plate-work  is  of 
universal  application;  each  case  presents  indications  which  should 
determine  what  form- of  prosthesis  is  applicable. 

The  work  has  unquestionably  a  great  field  of  useful  application: 
cases  there  are  in  which  this  type  of  fixture  is  a  well-defined  need,  and 
others  in  which  it  is  clearly  contraindicated. 

The  first  incjuiry  of  the  operator  should  be,  Is  a  bridge  demanded  by 
the  conditions  present  ?  that  is,  Does  a  bridge  device  possess  for  the  case 
in  hand  sufficient  advantage  over  a  plate  denture  to  render  its  use  an 
imperative  indication  ?  Upon  this  point  turns  the  entire  subject  of  the 
wisdom  or  unwisdom  of  ])ridge-work. 

The  student  is  assured  that  in  the  practice  of  this  special  field  he  will 
find  application  for  an  exhaustive  knowledge  of  dental  pathology,  thera- 
peutics and  mechanics,  combined  w^ith  rare  manipulative  ability;  in 
point  of  fact,  the  work  should  not  be  done  unless  the  operator  possess 
this  degree  of  knowledge  and  skill. 

The  requisites  for  its  correct  practice  mark  the  mechanical  and  phys- 
iological  aspects  of  bridge-work. 

Mechanical  Aspects. — Under  the  mechanical  aspect  are  inchuled  all 
considerations  of  resistances  to  stress  and  the  effect  of  stress  as  expres- 
sed in  the  mobility  of  the  bridge,  of  any  part  of  it,  or  of  its  abutments. 
Vhe  same  considerations  governing  the  mechanical  resistance  of  roots 


MECHANICAL  ASPECTS.  729 

or  teeth  when  serving  as  bases  for  artlfieial  crowns,  apply  with  increased 
emphasis  when  they  are  to  he  the  al)utnients  of  a  bridoe  piece. 

The  student  is  presumably  famihar  with  the  anatomy  and  the  ana- 
tomical variations  of  the  teeth  as  to  their  forms,  structure,  and  positions. 

Any  stress  greatly  in  excess  of  the  amount  normally  borne  is  a  menace 
to  the  integrity  of  a  tooth's  retention.  The  increased  mechanical 
stress  reacts  physiologically,  and  by  a  pathological  process  the  tooth  is 
loosened  and  lost. 

The  vertical  is  the  only  direction  of  force  which  does  not  tend  to 
mechanically  dislodge  a  tooth,  and  it  is  one  to  which  teeth  are  rarely 
subjected  alone.  As  a  rule,  teeth  protest  against  stress  received  in  any 
direction  other  than  that  due  to  their  anatomical  forms  and  positions. 
Incisors  are  by  these  factors  designed  to  meet  and  resist  stress — to  move 
in  one  direction,  either  outward  or  inward.  The  broadest  aspect  of 
their  root  is  anterior,  offering  at  this  part  the  greatest  resistive  surface. 

The  canines  receive  the  force  in  two  directions,  each  at  an  angle  with 
the  axis  of  the  tooth :  the  resultant  of  the  forces  (the  direction  of  the 
movement  of  the  tooth)  is  between  the  two  forces.  The  movement  will 
be  according  as  the  greater  impact  is  anterior  or  posterior  (Fig.  730  ). 

The  bicuspids  normally  receive  three  main  lines  of  force — an  outward, 
an  inward,  and  a  vertical :  the  outward  and  inward  forms 
are  the  resultants  each  of  two  forces  acting  upon  the  cusps        ^^°-  '^^^ 
at  an  angle  with  the  axis  of  the  tooth. 

The  muscular  force  being  equal,  the  longer  the  cusps 
the  greater  will  be  the  lateral  stress;  also  the  broader  the 
cusps  (the  farther  -  their  external  walls  are  removed  from 
the  axes  of  the  teeth)  the  greater  stress  there  will  be  in 
all  three  directions. 

The  molars   also  receive  force  in  three  main  directions, 
but  the  lateral  forces  are  the  resultants  of  several  lines  of  force  accord- 
ing to  the  sizes  and  positions  of  the  cusps. 

The  resistances  to  these  stresses  are  through  the  forms,  number, 
sizes,  and  structure  of  the  roots,  and  also  of  their  supporting  structures. 

Dr.  Bonwill  has  demonstrated  a  relationship  between  the  lengths  of 
the  cusps  and  the  amount  of  over-bite,  and  as  a  consequent  the  extent 
of  the  contact  of  the  cusps  in  mastication.  The  greater  the  over-bite 
the  greater  surface  of  contact  there  must  be,  and,  other  things  being 
equal,  the  greater  mechanical  stress.  This  is  an  important  consider- 
ation, and  one  to  be  constantly  borne  in  mind  in  the  making  and  ad- 
justing of  crowns  and  bridges. 

No  absolute,  or  perhaps  even  approximate,  rules  can  be  formulated 
as  to  the  amount  of  strain  any  single  tooth  will  bear:  attempts  at  the 
formulation  are  delusive.  Given  two  central  incisors,  the  amount  of 
resistance  either  will  afford  depends,  first,  upon  the  anatomical  form 
and  support  of  each,  and  their  relative  positions  to  their  antagonists, 
and  is  governed  largely  by  the  physiological  condition  of  each.  Alter 
the  relations  in  any  particular,  and  the  resistance  Is  correspondingly 
modified. 


730  --l-V  ASSKMBI.AGK  OF   UXITED  CliOWXS. 

In  the  upper  jaw,  the  central  incisors  are  stronger  teeth  than  the 
laterals.  The  canines  are  more  firmlv  imj)lantecl  than  the  bicuspids, 
or  any  of  the  anterior  teeth  and  constitute  the  best  abutments.  The 
bicuspids  form  good  anchorages  if  too  much  is  not  expected  of  them. 
The  first  and  second  molars  are  very  strong  and  make  good  abutments, 
but  the  third  molars  are  more  uncertain  and  cannot  be  depended  upon 
to  the  same  extent  as  the  first  and  second.  There  are  many  times 
however,  when  these  teeth  are  exceptionally  firm  and  strong  and  will 
do  their  share  of  the  work  in  supporting  a  bridge;  but  they  should  be 
examined  carefully  before  deciding  to  utilize  them.  One  probable  rea- 
son for  their  frefjuent  failure  to  render  satisfactory  service  is  the  fact  that 
as  they  are  situated  so  far  back  in  the  mouth  and  are  consequently  so 
difficult  to  get  at  for  trimming,  this  latter  operation  is  not  thoroughly 
done  and  the  bridge  fails.  The  fact  of  their  difficult  accessibility 
should  make  the  operator  more  careful  and  painstaking  in  their  pre- 
paration. 

In  the  lower  jaw,  the  lateral  incisors  are  stronger  than  the  centrals 
which  are  the  weakest  teeth  in  the  mouth; notwithstanding  this  fact, 
the  centrals  are  frequently  of  great  value  as  abutments  in  those  cases  in 
which  the  placing  of  a  bridge  would  be  impossible  without  their  use. 
The  relative  strength  of  the  other  teeth  in  this  jaw,  is  about  as  in  the 
corresponding  teeth  of  the  upper  jaw. 

The  form  of  the  arch  has  a  great  deal  to  do  with  the  carrying  capacity 
of  the  teeth.  A  bridge  which  in  one  mouth  would  be  of  the  utmost 
value  to  the  patient,  in  another,  with  exactly  the  same  anchorages,  all 
in  an  equally  good  condition,  but  with  the  arch  differently  formed,  might 
prove  impractical  or  useless. 

By  uniting  or  splinting  together  several  teeth,  as  in  a  bridge  piece, 
the  movement  of  each  tooth  is  modified  or  restrained,  and  by  such 
fixation  two  natural  teeth  are  frequently  found  to  withstand  successfully 
more  force  than  the  sum  of  their  individual  resistances.  As  an  illustra- 
tion observe  a  common  condition  in  which  a  bridge  is  applied —  a  lower 
second  bicuspid  and  a  third  molar  serving  as  abutment  teeth.  If  these 
teeth  be  healthy  and  have  firm  attachment,  fixing  to  them  a  rigid  bridge 
piece  prevents  the  tendency  tow^ard  antero-posterior  displacement,  one 
of  the  strongest  elements  tending  toward  their  loss;  they  are  held  by  the 
bridge  so  that  the  only  possible  movement  is  lateral. 

If  the  lateral  stress  be  correctly  governed,  such  teeth  may  safely  bear 
crowns  upon  their  own  roots,  and  support  intervening  crowns,  filling 
the  space  betw^een  them,  for  a  longer  period  than  were  a  bridge  not  ap- 
plied. 

One  of  the  most  common  faults  of  bridge-work  is,  however,  increas- 
ing strains  w^ithout  due  regard  to  the  available  resistance. 

Using  the  same  bridge  for  illustration,  the  abutments  are  subjected  to 
the  amount  of  stress  normally  borne  by  four  teeth.  It  depends  upon  the 
directions  of  the  root-axes  whether  the  resistance  of  the  abutments 
when  barred  together  is  increased  in  the  same  degree  as  the  stress. 
Their  antero-posterior  movement  is  effectually  checked,  but  if  the  roots 


MECHA  MCA  f.  A  SPECTS. 


■:U 


of  the  teeth  have  parallel  axe.s,  both  are  free  to  react  upon  lateral  stress. 
While  abutment  teeth  submit  without  protest,  as  a  rule,  to  the  direct 
vertical  force  of  mastication,  occasionally  there  will  be  found  a  pro- 
gressive degeneration  of  the  pericementum,  which  causes  loosening  of 
these   teeth. 

The  lateral  stress  is  the  one  tending  to  dislodge  bridge  fixtures,  and 
the  tendency  to  displacement  is  increased  in  the  ratio  of  this  stress 
hence  the  longer  the  cusps,  and  the  more  accurate  their  occlusal  union 
with  the  antagonizing  teeth,  the  greater  the  stress  upon  the  abutments. 

Bridge-work  should  be  constructed  upon  sound  mechanical  princi- 
ples :  to  be  successful  as  a  piece  of  engineering  work,  all  designs  are  to  be 
founded  upon  those  principles.  These  fixtures  are  literally  bridges,  a 
continuous  surface  supported  by  rigid  abutments,  designed  to  bear 


Fig.  731 


i.c--     ^./^ 


safely  the  amount  of  stress  It  is  calculated  the  piece  will  be  subjected 
to.  The  calculations  involve  the  strengths  of  abutments,  crowns,  and 
body  of  the  bridge.  Violations  of  sound  engineering  principles  are 
common  in  suggested  dcA'ices:  the  students  should  examine  carefully 
all  proposed  designs  and  select  only  those  which  are  mechanically  good. 

An  engineer  recognizes  that  the  stability  and  permanence  of  his 
bridge  depends  primarily  upon  the  strength  and  position  of  its  abut- 
ments. If  these  be  badly  built  or  poorly  sustained,  the  bridge  fails; 
so  that  bases  are  selected  and  prepared,  abutments  built,  wdth  a  due 
regard  for  the  weight  they  are  to  sustain,  the  resistance  they  are  to 
afford. 

With  dental  bridges,  utilizing  any  but  sound  teeth  or  roots,  those  free 
from  pericementitis  or  abscess,is  equivalent  to  an  engineer  building  abut- 
ments in  a  marsh  wdthout  piles. 


732  AN  ASSEMBLAGE  OF  UNITED  CROWNS. 

In  (lesifjninf;  a  bridge  note  the  dirt'ctions  of  the  least  and  greatest  re- 
sistances, and  ai)|)l\'  the  strains  accor(lin^l\',  and  mold  the  artienlation 
so  that  the  i;reatest  force  shall  he  o])i)()sed  to  the  greatest  resistance  and 
vice  versa.  To  illustrate:  teeth  which  have  their  axes  i)arallel  and  in 
the  same  plane  (Fig.  731),  all  other  things  being  equal,  will  withstand 
less  stress  than  were  the  axes  not  parallel  and  in  different  planes  (Fig. 
732);  that  is,  when  the  teeth  in  l)oth  cases  are  serving  as  bridge  abut- 
ments: with  parallel  axes,  when  one  abutment  moves  in  the  direction  of 
least  resistance  its  fellow  abutment  moves  with  it;  but  if  the  axes  be  not 
parallel,  when  one  abutment  is  subjected  to  stress  iti  the  line  of  least  re- 
sistance its  fellow  is  receiving  the  stress  in  a  line  of  greater  resistance. 

Another  illustration  is  found  in  a  common  form  of  bridge — two  canine 
roots  supporting  artificial  crown  subsitutes  of  the  six  anterior  teeth 
(Fig.  733.).  With  all  of  the  posterior  teeth  in  position  the  amount  of 
strain  on  the  abutments  is  governed  first  by  the  lengths  of  the  crowns, 
the  leverage  on  the  roots;  next  upon  the  amount  of  over-bite  or  the  ex- 
tent of  incisive  action  occurring  before  the 
Fi<^-  '■^^^  occlusion    of  the    posterior  teeth    equalizes 

the  forces.  In  the  ratio  of  the  stress  is  the 
demand  for  increased  resistance:  such  cases 
form  bulkheads,  and  if  the  displacing  force 
be  great,  the  ends  of  the  bulkhead  require  re- 
inforcement through  additional  abutments. 
To  ensure  the  stability  of  a  bridge  it 
should  be  so  made  and  so  attached  to  its  abutments  that  neither 
bridge  nor  any  part  of  it  has  any  movement  independent  of  the  abut- 
ments. Violations  of  this  rule  are  found  where  caps  are  made  of  too 
thin  metal,  which  by  stretching  or  breaking  permit  slight  loosening  of 
the  piece;  the  retaining  cement  is  worn  away  piecemeal,  and  the  space 
left  is  filled  with  fermenting  debris:  decalcification  of  the  enamel  and 
caries  ensue. 

With  decreasing  amount  of  resistance  offered  by  the  abutments 
should  be  a  decrease  of  the  extent  of  masticating  or  incisive  surface; 
for  example,  two  abutment  crowns,  a  firmly  fixed  molar  and  canine, 
having  healthy  root  support,  may  have  the  original  amount  of  masti- 
catory surface  restored;  but  if  the  fixation  of  the  abutments  be  less 
rigid  or  not  in  so  good  a  physiological  condition,  the  amount  of  the  sur- 
face should  be  diminished. 

It  is  not  possible  for  one  to  specify  all  of  the  situations  for  which 
bridge-work  is  suitable,  but  we  can  endeavor  in  a  general  way  to  give 
an  idea  of  what  may  be  expected  of  the  different  teeth.  No  two  cases 
are  alike  and  each  one  should  be  studied  by  itself  and  a  judgment 
formed  according  to  the  conditions  existing  in  the  individual  case. 
We  shall  begin  at  the  anterior  part  of  the  mouth. 

Where  the  two  lateral  incisors  have  been  lost,  the  central  roots  may 
be  safely  trusted  to  support  both  lateral  dummies,  but  it  would  not  be 
reasonable  to  expect  them  to  do  more.  Where  the  centrals  are  mis- 
sing, the  lateral  roots  are  usually  sufficiently  strong  to  carry  a  bridge 


PHYSIOLOGICAL  ASPECT.  733 

restoring  the  former,  but  in  tlie  case  of  an  exaggerated  V-shaped  arch, 
the  leverage  of  such  a  bridge  might  cause  sufficient  strain  on  the  roots 
to  dislodge  them.  A  right  central  and  left  lateral  will  carry  the  left 
central  and  right  lateral  dummies  and  vice-versa.  Where  all  of  the 
incisors  have  been  lost,  if  the  arch  is  broad  and  the  canines  stand  well 
apart,  so  that  the  teeth  to  be  restored  may  be  placed  in  nearly  a  straight 
line,  a  serviceable  bridge  may  be  made  with  a  reasonable  expectancy 
that  it  will  last  for  many  years. 

Where  the  arch  is  very  narrow  or  V-shaped  and  the  canines  are  close 
together,  so  that  the  incisors  have  to  be  placed  in  a  marked  curve  out- 
ward, projecting  far  beyond  the  line  of  the  abutments,  it  would  be  risk- 
ing a  great  deal  to  trust  to  the  canines  alone  to  carry  such  a  bridge.  If 
the  bridge  is  extended  so  as  to  take  in  the  bicuspids,  it  will  make  a  much 
stronger  piece,  as  these  two  additional  anchorages  will  render  it  more 
rigid,  and  the  resistance  of  the  broad  masticating  surfaces  of  the  bicus- 
pids will  make  it  less  liable  to  tilt  upward  in  the  front.  These  condi- 
tions obtain  more  especially  in  cases  of  fixed  bridges. 

WQiere  the  six  anterior  teeth  are  lost,  it  is  perhaps  as  well  to  give  up 
the  thought  of  bridge-work  and  to  trust  to  a  plate;  however,  under 
certain  conditions  a  satisfactory  removable  bridge  might  be  made  for 
the  case. 

To  place  a  bridge  from  the  canine  to  the  first  molar,  or  even  to  the 
the  second,  is  good  practice,  and  at  times  it  might  even  be  extended  to 
the  third.  The  first  or  second  bicuspid  and  the  second  or  third  molar 
will  give  good  support.  Where  all  of  the  molars  are  lost,  they  can  only 
be  restored  with  the  removable  type  of  bridge. 

In  order  to  restore  the  full  set  of  teeth  in  the  upper  jaw,  there  should 
be  at  least  four  good  strong  roots  to  serve  as  abutments,  as  for  example, 
the  two  canines  and  a  first  or  second  molar  on  each  side.  Where  the 
two  central  roots  are  also  in  position,  of  course,  they  give  greater 
strength  to  the  piece  and  each  additional  root  adds  just  so  much  to  the 
chances  of  long  life  for  the  bridge. 

A  larger  bridge  may  be  placed  on  the  same  number  of  roots  in  the 
lower  jaw  than  in  the  upper,  as,  having  gravity  in  its  favor,  the  choice  of 
a  saddle  piece  is  possible,  which  could  not  be  thought  of  in  the  upper 
jaw.     Of  course,  it  must  be  made  removable. 

Physiological  Aspect. — The  physiological  aspect  of  bridge-work, 
although  belonging  properly  to  works  upon  dental  pathology,  must 
form  part  of  every  treatise  upon  such  a  combination  of  surgery  and 
mechanics  as  bridge-work  represents.  It  includes  the  consideration 
of  all  of  the  vital  relations  of  the  abutment  teeth,  the  contiguous  parts, 
and,  it  may  be,  of  more  general  vital  relations.  Anything  directly  or 
indirectly  bearing  upon  the  subject  of  dental  hygiene  is  an  item  for  con- 
sideration in  the  pursuit  of  this  work. 

The  first  question  is  that  of  the  physiological  resistance  of  the  abut- 
ments, and  the  danger,  immediate  or  remote,  of  any  disease  process 
occurring  in  or  about  them.  These  include  the  possibilities  of  enamel 
decalcification,  caries  of  the  dentine,  eburnitis,  any  stage  or  degree  of 


734  AX  ASSEMBLACE  OE   UMTElJ  CROWXS. 

pulp  irritation  or  inflammation,  and  any  variety  or  degree  of  perice- 
mentitis. The  possibility  or  probability  of  any  one  or  more  of  these  con- 
ditions arising  must  be  a  governing  factor  in  determining  the  form  of 
bridge  to  be  applied. 

Due  consideration  must  be  given  to  the  possibility  of  disease  process 
of  the  soft  tissues — whether  through  too  great  or  improper  character  of 
contact  the  gums  be  irritated  by  pressure  or  the  contact  of  sharp  edges, 
or  the  forming  of  spaces  in  which  decomposing  food  may  act  as  an  ir- 
ritant to  mucous  surfaces. 

The  decalcification  of  an  enamel  surface  embraced  by  a  portion  of 
the  bridge  arises  from  lactic  acid,  the  product  of  a  specific  fermentation 
of  starchy  foods  gaining  access  to  surfaces  from  which  it  is  not  removed, 
due  either  to  the  carelessness  of  a  patient  or  to  his  inability  to  remove 
it  owing  to  the  peculiar  situation. 

Undec  narrow  bands  or  where  the  retaining  cement  is  exposed  to  the 
access  of  the  fluids  of  the  mouth,  after  a  variable  length  of  time  it  is 
mechanically  dislodged,  or  it  may  be  dissolved,  leaving  a  space  which 
fills  with  fermenting  materials  inaccessible  to  the  tooth-brush.  Pock- 
ets made  by  some  surface  of  the  bridge  and  an  uncovered  enamel 
surface  become  filled  with  fermenting  deposits,  which  if  not  removed 
produce  decalcification  of  the  enamel  surface.  If  these  spaces  remain 
undetected,  caries  follows,  and  it  may  be  exposure  and  disease  of  the 
pulp,  and  subsequently  of  the  pericementum. 

Bridges  should  be  so  made  and  so  placed  that  even  less  opportunity 
is  given  for  the  action  of  the  products  of  fermentation  upon  tooth-tissues 
than  before  the  placement  of  the  bridge. 

Any  part  of  a  tooth's  surface  which,  through  the  fixing  of  a  bridge, 
is  placed  beyond  the  access  of  the  ordinary  cleansing  agents  employed 
by  patients  should  be  protected  from  the  ingress  or  contact  of  ferments 
or  fermentable  material  by  having  a  portion  of  the  bridge  act  as  an 
impenetrable  and  impermeable  shield. 

Another  possible  source  of  disturbance,  one  which  may  affect  the 
nutritive  functions  of  the  pulp,  will  be  found  in  teeth  which  have  been 
denuded  of  enamel  by  their  preparation  to  serve  as  abutments.  The 
pulp  may  receive  abnormal  stimulus  through  the  irritation  of  the  con- 
tents of  the  dentinal  tubuli  or  have  an  increased  conduction  of  thermal 
influence,  and  secondary  deposits  may  occur  in  the  pulp. 

The  question  of  subsequent  pericementitis  in  an  abutment  tooth,  if 
the  tooth  be  pulpless,  depends  largely  upon  the  thoroughness  with 
which  the  pulp-canal  and  dentine  have  been  sterilized,  and  the  com- 
pleteness with  which  an  impenetrable  barrier  has  been  placed  between 
the  pulp-canal  and  the  tissues  of  the  apical  region;  second,  upon  the 
former  condition  of  the  root,  as  a  part  once  inflamed  has  an  increased 
susceptibility  to  a  recurrence  of  inflammation;  third,  overstraining  the 
abutments,  causing  a  chronic  pericementitis  and  a  gradual  loss  of  the 
alveolar  tissues;  fourth,  the  existence  of  a  dyscrasia  which  may  in  the 
future  cause  phagedenic  pericementitis.  Should  any  of  the  pathologic 
states  be  present,  they  must  receive  appropriate  treatment  before  the 


PREPARATION  OF  ABUTMENTS 


7:]5 


fixation  of  the  bridge.  Should  they  arise  subsequently,  each  must  re- 
ceive therapeutic  aid. 

The  muco-periosteum  of  the  alveolar  ridge  most  suitable  for  the 
contact  of  bridge  pieces  is  that  exhibiting  firm  texture  and  pink  color. 
When  placed  in  mouths  exhibiting  a  catarrhal  condition  increased  care 
is  demanded  that  there  be  no  inaccessible  pockets  in  which  fermenting 
material  may  find  lodgement. 

When  the  retaining  medium  of  a  bridge  is  zinc  phosphate,  it  should 
be  so  protected  by  the  bridge  that  the  fluids  of  the  mouth  have  httle  or 
no  access  to  it. 

Contact  of  any  portion  of  a  bridge  with  the  natural  gum  should  be 
of  such  a  nature  that  there  is  established  no  source  of  irritation  to  it. 

Fig.  734 


either  through  roughness,  sharp  edges,  undue  pressure,  or  inaccessible 
pockets. 

Preparation  of  Abutments. — First  and  most  important,  any  root  or 
tooth  which  it  is  designed  to  make  the  abutment  of  a  dental  bridge 
should  have  such  preliminary  treatment  as  will  bring  it  to  a  condition 
of  health.  The  directions  given  as  to  the  preparation  of  roots  for  the 
reception  of  artificial  crowns  apply  with  redoubled  force  when  these 
roots  are  to  be  abutments.  The  same  requirements  as  to  perfect  adap- 
tation of  individual  crowns  also  obtain  when  such  pieces  are  to  serve 
as  the  abutment  crowns  of  bridges.  The  contact  of  every  crown  edge 
with  its  base  should  be  perfect,  and  each  crown  should  represent  as 
carefully  made  and  adjusted  a  piece  as  were  the  same  crown  to  stand 
alone. 

After  all  preparations  of  the  bases  have  been  made,  so  that  single 
crowns  may  be  properly  adapted,  there  arises  the  consideration  of  the 


736  AN  ASSEMBLAGE  OF   UNITED  CROWNS. 

mutual  relatious  botweeu  the  iudixidual  crowus.  It  is  evident  that  as 
these  pieces  are  to  be  rigidly  joined  to  one  immovable  piece,  the  abut- 
ments must  be  so  shaped  as  to  permit  placing  them  when  so  joined. 
The  next  consideration  is,  therefore,  the  dressing  of  the  walls  of  the 
abutments  until  they  are  parallel  or  less  than  parallel,  for  it  is  also  evi- 
dent that  if  the  distance  .1.1  be  less  than  B  Ji  (Fig.  734),  joined  cyl- 
inders which  shall  slip  over  A  A  will  not  be  in  contact  with  the  points 
B  B;  and  this  latter  is  an  essential  condition  in  properly  adapted  abut- 
ment crowns.  (See  also  Fig.  736.)  With  post  crowns  it  is  evident 
that  the  axis  of  the  root-canal,  the  root-walls  covered  by  the  collar,  and 
the  walls  of  the  other  abutment  must  all  be  parallel  or  they  cannot  be 
perfectly  set  when  rigidly  united.  The  placing  of  a  wire  in  the  ])rei)ared 
root-canal  will  assist  in  a  judgment  of  this.  The  lack  of  parallelism  is 
shown  in  F'ig.  735. 

The  extent  of  the  lack  of  parallelism  between  the  axes  of  the  abut- 
ments are  noted  before  preparing  the  latter  for  the  reception  of  the 

abutment  crowns.      A  pair  of  accurate 

^^°-  "^^^  callipers   will  be  found   useful  to  make 

1  !       measurements  to  determine  the  amount  of 

dressing  required.  Applied  first  to  the 
longest  distance  between  the  abutments, 
usually  at  the  necks  of  the  teeth,  this  length 
is  laid  upon  the  parts  with  shortest  dis- 
tance. The  portions  of  the  tooth  neces- 
sary to  equalize  the  lengths  are  then 
dressed  away.  Should  the  teeth  diverge, 
j  j       the  shortest  distance   is   first  measured, 

I       and  the  dressing  of  the  w^alls  proceeded 
with  as  before. 
To  allow  of  slight  aberrations  in  adjusting  it  is  usual  to  reduce  the 
walls  to  something  less  than  mutually  parallel  lines. 

Requisites  of  a  Correct  Bridge.— The  first  requisite  is  that  a  dental 
bridge  must  be  regarded  as  a  prosthetic  appliance  in  its  fullest  sense :  it 
should  restore  as  nearly  as  possible  lost  form,  appearance,  and  function. 
It  should,  therefore,  restore  the  general  contour  lost  through  the  loss  of 
the  teeth,  and  reproduce  the  forms  of  the  natural  crowns.  The  pieces 
should  be  constructed  for  aesthetic  effect  with  the  same  care  as  with  a 
plate  denture.  The  teeth  should  be  selected  with  the  same  regard  to 
their  proper  sizes,  shapes,  and  colors  as  with  plate  dentures.  The 
same  care  is  to  be  exercised  in  accurately  adapting  crowns  as  when 
these  fixtures  are  made  and  ^^^m\  as  single  crowns.     These  details  are 


sed  in  a 
ledf^ni 


frequently  ignored  or  deemed^^iinor  importance — a  view  to  which  the 
student  should  by  no  means  subscribe.  The  masticating  surfaces  are 
to  be  so  formed  that  they  wull  occlude  perfectly  with  the  antagonizing 
teeth ;  moreover,  so  that  they  shall  effectively  perform  the  work  of  actual 
mastication  to  an  extent  commensurate  with  the  resistance  of  the  abut- 
ments. 

It  is  unwise  to  make  the  restoration  in  this  particular  too  complete: 


MAXUFACTURER  OF  DEXTAL  BRIDGES.  737 

that  is,  by  restoring  full  cusp  lengths  and  full  occluding  surfaces,  as 
would  be  the  case  were  an  anatomical  articulator  used  and  the  teeth 
perfect  anatomical  representatives  of  the  lost  organs.  The  occluding 
surfaces  are  given  a  smaller  area,  and  the  cusps  made  shorter  than  with 
the  natural  teeth,  so  that  the  vertical  and  lateral  forces  upon  the  abut- 
ments are  lessened  to  the  recjuired  degree.  This  only  applies  to  cases 
where  all  of  the  posterior  teeth  on  both  sides  of  the  mouth  are  to  be  re- 
stored. If  the  natural  teeth  are  all  in  position  on  one  side  of  the 
mouth,  in  a  bridge  restoring  the  lost  molars  or  bicuspids  on  the  op- 
posite side,  the  cusps  should  be  made  to  correspond  to  the  cusps  of  the 
natural  teeth.  When  the  jaws  are  in  normal  closure,  however,  the  oc- 
clusion should  be  perfectly  accurate  or  else  the  usefulness  of  the  piece 
is  lessened. 

If  possible,  every  portion  of  the  bridge  and  abutments  above  the  gum 
line  should  be  easily  accessible  to  the  bristles  of  a  tooth-brush.  Tooth- 
substance  should  form  no  wall  of  a  pocket  inaccessible  to  the  same 
implement.  The  bridge  should  cover  and  seal  such  surfaces.  It  should 
be  sufficiently  rigid  in  all  its  parts,  and  be  so  firmly  attached  to  its  abut- 
ments that  abutments,  bridge,  and  all  its  parts  are  a  rigid  piece,  having 
not  the  least  movement  except  as  a  single  piece.  It  is  essential  that  the 
abutments  or  their  crowns  have  no  movement  upon  one  another.  This 
necessitates  that  each  crown  shall  be  in  itself  sufficiently  rigid  to  resist 
any  change  of  form  through  the  stress  of  mastication.  It  is  not  alone 
necessary  that  a  crown  shall  fit  an  abutment  perfectly;  it  must  continue 
to  do  so. 

As  stated  earlier  in  this  chapter,  there  should  be  in  the  placing  of  a 
bridge  a  diminution  rather  than  an  increase  of  the  opportunities  for 
disease  process  arising.  All  edges  which  come  in  contact  with  the  soft 
tissues  should  be  smoothed  and  rounded.  Every  surface  of  the  bridge 
should  be  free  from  inequalities  or  mechanical  blemish  of  any  kind. 

THE  MANUFACTURE  OF  DENTAL  BRIDGES. 

There  are  involved  in  the  making  of  a  bridge  three  sets  of  manipu- 
lations: first,  the  making  of  the  abutment  crowns;  second,  the  manu- 
facture of  the  intervening  dummies;  and,  third,  the  uniting  of  the 
several  parts  into  one  rigid,  highly  finished  piece.  From  beginning  to 
end  it  includes  a  series  of  small  but  important  details.  In  the  degree 
that  care  and  attention  are  devoted  to  these  minutiae  will  be  the  accuracy 
of  fit  and  finish  of  the  completed  bridge  y^k^t  of  them  may  be  followed 
by  blemish  or  even  by  disaster.  ^^^ 

.Esthetic  considerations  are  too  frequently  ignored  in  this  class  of 
work,  but  they  are  equally  important  in  this  as  in  any  prosthetic  opera- 
tion. The  completed  piece  should  present  a  restoration  as  nearly  as 
possible  of  the  forms,  color,  size,  and  positions  of  the  natural  organs, 
and  should  be  so  articulated  as  to  restore  the  lost  masticating  surfaces. 

Unnecessary  exposure  of  gold  is  to  be  avoided,  and  yet  the  several 
47 


7,38  AN  ASSEMBLAGE  OF  UNITED  CROWNS. 

porcelain  pieces  are  to  be  so  guarded  that  they  serve  merel}  for  the 
restoration  of  appearances,  receiving  tliemselves  no  direct  force,  the 
latter  bearing  only  upon  masticating  surfaces  of  gold.  By  this  means 
fracture  of  the  porcelain  becomes  a  remote  possibility. 

We  shall  now  consider  the  making  of  a  bridge  and  shall  select  as  a 
common  type,  one  of  two  full  gold  crowns,  or  of  one  full  gold  crown 
and  a  Richmond,  carrying  one  or  more  dummies.  The  abutment 
pieces  having  been  adjusted  to  their  respective  positions,  the  impression 
and  articulation  are  taken  and  the  cast  prepared  in  the  manner  already 
described. 

In  selecting  the  facings  for  the  case  it  is  desirable  to  choose  them  of 
such  length  that  when  they  are  ground  into  place,  the  necks  will  just 
touch  the  gum  lightly  and  the  occlusal  edges  will  be  in  contact  wdth 
the  antagonizing  teeth.  They  are  ground  to  follow  the  gum  line  and 
should  not  be  in  actual  contact  with  each  other.  After  they  have  been 
ground  into  place,  a  wall  of  plaster  is  built  up  on  the  buccal  side  of  the 
cast  to  retain  them  in  position.  After  the  plaster  has  hardened  the 
facings  are  removed,  and  their  occlusal  ends  ground  off  about  one  thir- 
ty-second of  an  inch  and  at  an  angle  of  about  forty-five  degrees  with  the 

Fig.  737  Fig.    738  Fig.  739  Fig.    740 


back  of  the  facing.  (Fig.  737.)  The  line  of  their  occlusal  ends  should 
be  continuous,  that  is,  the  bevel  of  one  facing  should  not  be  higher  than 
another.  The  facings  are  then  to  be  backed  and  for  this  purpose, 
platinum,  crown  metal  or  pure  gold  may  be  used.  The  gold  will  have 
a  tendency  to  lighten  the  color  of  the  facing  and  give  it  a  slightly  yellower 
cast,  wdiile  the  platinum  will  tend  to  darken  it  and  confer  a  bluish  tint. 
If  the  backing  is  of  platinum,  it  may  be  very  thin,  about  three  one- 
thousandths  of  an  inch.  It  should  extend  from  the  inner  edge  of  the 
bevel  at  the  occlusal  end,  to  and  about  one-sixteenth  of  an  inch  over 
the  lower  edge  where  it  has  been  ground  to  fit  the  gum.  (Fig.  73S.) 
The  backing  of  each  facing  should  touch  or  slightly  overlap  that  of 
the  one  next  adjoining  and  those  of  the  end  facings  should  be  in  contact 
with  the  abutment  crowns.  (Fig.  739.)  The  pins  are  flattened  with  a 
pair  of  pin-roughening  pliers,  and  are  bent  down  over  the  backing,  thus 
pressing  it  close  to  the  facing.  The  facings  are  then  waxed  together 
and  to  the  abutment  crowns  with  hard  adhesive  wax,  a  piece  of  oiled 
paper  being  placed  underneath  on  the  surface  of  the  cast  to  prevent 
their  attachment  to  it.  The  wax  should  be  built  up  high  enough  to 
support  the  cusps  for  the  dummies.    (Fig.  740.)     Suitable  solid  cusds 


SELECTION  OF  FACINGS. 


739 


are  then  made,  o-round  or  filed  to  fit  the  he\el  of  the  facings,  and  fast- 
ened in  phice  with  adhesive  wax.     (Fig.  741.) 

The  bridge  is  now  ready  for  investing  and  soldering.  It  is  taken 
from  the  cast,  the  inner  cap  being  removed  also  if  it  be  a  removable 
bridge,  and  the  inside  of  the  abutment  pieces  filled  with  the  investing 
material  and  the  whole  bridge  partly  imbedded  in  it  with  the  facings 
down.  The  in\estment  should  come  over  the  backings  which  extend 
beyond  the  lower  angle  of  the  facings,  holding  them  in  place  and  pre- 
venting their  springing  up.  (Fig.  742.)  The  investment  should  come 
nearly  to  the  lingual  edge  of  the  cusp  (Fig.  742),  and  should  be  small, 
and  only  large  enough  to  hold  the  parts  together.  The  abutment  crowns 
are  partly  covered  to  protect  them  from  the  flame. 

In  grinding  the  facings  for  the  dummies  for  any  of  the  six  anterior 
teeth  they  should  be  made  to  set  closely  to  the  cast,  and  after  they  are 
properly  fitted  a  wall  of  plaster  is  made  on  the  labial  side.  The  facings 
are  then  backed,  the  backings  extending  over  the  beveled  portion  at  the 
neck  and  about  one-sixteenth  of  an  inch  beyond  the  incisal  edge  (Fig. 
743),  and  the  pins  flattened  and  bent  toward  this  edge  close  to  the  back- 


Fia.  741 


Fig.  742 


Fig.  74^ 


Fig.  744 


ing.     In  investing,  the  investment  should  cover  the  extending  portion 
of  the  backing  to  prevent  its  warping.     (Fig.  744.) 

Bridges  of  three  or  four  teeth  may  be  soldered  in  one  piece,  but  large 
cases  should  be  soldered  in  sections.  This  is  because  the  contrac- 
tion of  large  masses  of  solder  when  the  piece  cools  has  the  effect  of 
disturbing  the  relation  of  the  abutment  pieces,  and  the  bridge  in  con- 
sequence has  its  fit  impaired.  A  full  bridge  of  twelve  or  fourteen  teeth 
should  be  soldered  in  three  or  four  sections.  If  in  three,  the  incisors 
may  be  soldered  in  one  piece,  and  the  sides  from  the  canine  back 
separately.  If  in  four  sections,  the  central,  lateral  and  canine  of  each 
side  separately  and  then  the  side  bridges.  The  different  sections  are 
then  finished  and  polished  except  where  they  are  to  be  united.  They 
are  then  replaced  on  the  cast,  waxed  together  with  adhesive  wax  and 
a  strong  iron  or  brass  wire  bent  to  conform  to  the  lingual  side  of  the 
bridge  and  waxed  firmly  to  the  different  parts.  This  will  hold  them 
firmly  in  their  proper  relative  positions  and  prevent  their  springing 
while  being  removed  from  the  cast  and  invested.  The  bridge  is  then 
invested,  the  di^^sions  between  the  several  sections  being  freely  ex- 
posed and  the  parts  united  with  the  same,  or  a  slightly  low^er  carat 
solder  than  has  been  used  in  the  previous  soldering.  \\Tien  the  invest- 
ment has  cooled,  the  bridge  is  removed,  pickled  in  dilute  sulphuric 
acid  and  finished. 


740  AN  ASSEMBLAGE  OF  UNITED  CROWNS. 

Selection  of  Facings. — In  choosing  the  facings  for  crowns  or  a  bridge, 
or  in  fact  for  any  form  of  partial  denture,  the  greatest  care  should  be 
used  to  select  those  of  proper  mold  and  shade.  If  it  is  impossible  to 
get  a  facing  to  match  exactly  the  shade  of  the  natural  teeth,  it  is  better 
that  it  should  be  slightly  darker  rather  than  hghter  than  these.  If 
a  crown  is  the  least  bit  too  light  in  color  it  is  conspicuous  and  is  the  first 
thing  seen  when  the  patient  opens  the  mouth,  while  if  it  is  but  slightly 
darker  than  the  neighboring  teeth  is  not  so  noticeal)le. 

In  restoring  the  six  anterior  teeth,  the  facings  should  never  be  bought 
in  sets  as  put  up  by  the  manufacturers.  In  the  human  mouth,  these 
teeth  are  never  all  of  the  same  shade.  The  central  incisors  have  gen- 
erally a  yellowish  cast.  The  laterals  are  of  a  bluish  tint,  especially  at 
the  incisal  edge,  while  the  canines  are  the  yellowest  teeth  in  the  mouth 
anterior  to  the  molars.  If  the  facings  restoring  these  teeth  are  all  of  one 
color,  they  will  never  present  a  natural  appearance  since  their  unifor- 
mity will  at  once  advertise  their  artificial  nature.  They  should  be 
selected  in  pairs,  the  centrals,  laterals  and  canines,  each  from  a  different 
set  in  accordance  with  the  natural  shading  of  these  teeth. 

As  we  go  farther  back  in  the  mouth,  we  find  the  bicuspids  have  a 
tendency  toward  blueness  again,  while  the  molars  are  yellow.  In  select- 
ing these  teeth,  the  bicuspids,  especially  the  first,  should  be  matched 
as  nearly  as  possible.  With  the  molars  there  is  not  the  same  neces- 
sity of  being  so  exact.  They  should  be  of  the  same  general  shade  and 
may  be  darker  than  the  natural  teeth,  but  certainly  not  lighter. 

The  shape  of  the  teeth  should  be  studied  carefully  and  the  form 
of  those  lost  should  be  reproduced  as  nearly  as  possible  by  their  sub- 
stitutes. A  flat  facing  should  never  be  used  to  restore  a  tooth  which 
had  a  rounded  face.  The  remaining  natural  teeth  will  here  again  serve 
as  an  index  for  the  form  of  the  selected  facings. 

Occlusion. ^In  addition  to  its  other  rec[uirements,  the  articulation 
of  a  bridge  piece  must  be  as  nearly  perfect  as  it  is  possible  to  make  it. 
This  is  a  most  important  consideration  and  one  to  which  there  is,  seem- 
ingly, yery  little  attention  given  in  this  work.  A  bridge  which  is  properly 
articulated  will  not  only  be  more  effective  than  one  faulty  in  this  regard 
but  its  use  will  be  attended  with  less  liability  of  loosening  or  injurng 
the  abutments. 

A  large  percentage  of  the  cases  of  bridge-work  are  for  the  posterior 
part  of  the  mouth  and  the  dentist  is  most  frequently  called  upon  to  re- 
store lost  molars  and  bicuspids.  Where  these  teeth  in  either  jaw, 
have  been  lost  for  any  length  of  time  their  opponents  in  the  opposite 
jaw  are  sure  to  have  elongated  to  a  greater  or  less  extent  (Fig.  745),  and 
if  no  measure  is  undertaken  to  prevent,  they  will  eventually  be  exfoli- 
ated. The  normal  line  of  occlusion  must  be  restored  in  a  case  of  this 
description,  if  a  satisfactory  denture  is  to  be  made  to  replace  the  lost 
teeth,  whether  it  be  a  plate  or  a  bridge.  If  a  bridge  is  constructed 
without  doing  this,  it  can  be  never  so  serviceable  to  the  patient  as  where 
the  occlusion  has  been  made  normal.  The  triturating  motion  so  neces- 
sary for  the  perfect  performance    of  the  masticatory    function,  is  in- 


BRIDGES  WITH  BREAKS  IN  THEIR  BODY. 


741 


terfered  with  or  prevented  altogether,  the  only  movements  possible 
being  the  opening  and  closing  of  the  jaws  in  which  the  food  may  be 
pressed  or  crushed,  but  not  ground.  The  moment  the  mandible  is 
thrust  the  least  bit  forward,  the  jaws  are  thrown  apart  and  the  only 
point  of  contact  is  the  distal  cusp  of  the  elongated  molar,  with  the  me- 
sial cusp  of  the  lower  molar  opposite.  (Fig.  746.)  Where  this  elon- 
gation of  the  teeth  has  taken  place,  the  cusps  must  be  ground  away  to 
the  normal  line  of  occlusion  and  the  teeth  carved  so  as  to  reproduce  as 


Fig.  745 


Fig.  746 


nearly  as  possible  the  original  cusps.  If  they  have  become  very  much 
elongated,  it  may  be  necessary  to  devitalize  and  crown  them,  or  to  re- 
store their  masticating  surfaces  by  building  up  with  gold. 


BRIDGES  WITH  BREAKS  IN  THE  CONTINUITY  OF  THEIR  BODY. 

Cases  present  which  may  exhibit  conditions  favorable  for  the  employ- 
ment of  bridge-work,  except  that  at  some  part  of  the  arch  there  is  a 
tooth  which  may  be  mechanically  unnecessary  in  the  support  of  a 
bridge,  and  which  it  is  the  part  of  wisdom  to  leave  out  of  the  bridge 
structure.  It  may  be  that  the  tooth  has  such  a  lack  of  parallelism  be- 
tween its  axes  and  those  of  the  abutments  that  its  utilization  is  imprac- 


FiG.  747 


Fig.  748 


ticable.     The  author  of  the  only  satisfactory  device  for  application  in 
such  cases  is  Dr.  J.  L.  Wilhams.  ^ 

The  connecting  bars  may  be  formed  by  anneahng  and  slightly  flatten- 
ing bars  of  iridio-platinum  wire  No.  14;  these  are  bent  about  the 
necks  of  the  teeth,  not  quite  touching  them,  their  ends  resting  solidly 
against  the  stays  of  the  dummies.  A  typical  case  is  illustrated  in  Figs. 
747-749.     A  modified  form  of  the  same  device  is  seen  in  Fig.  750. 

1  The  Dental  Cosmos,.  Vol.  xxvii,  p.  705. 


742 


AN  ASSEMBLAGE  OF  UNITED  CROWNS. 


The  device  proves  useful  in  such  cases  as  the   following:   a  crownless 
lateral  with  a  good  root;  an  unblemished  canine;  the  first  bicuspid  ab- 


FiG.  749 


sent  and  the  second  bicuspid  root  fit  to  serve  as  an  abutment.    A  bridge 
is  constructed,  the  lateral  and  second  bicuspid  having  abutment  crown.s 

Fig.  750 


adapted;  a  dummy  replaces  the  first  bicuspid,  and  the  connecting  bar 
passes  around  the  palatal  portion  of  the  canine,  resting  lightly  upon  the 
gum. 


REMOVABLE  BRIDGES.  74;J 

EXTENSION  BRIDGES. 

The  principle  of  construction  of  this  variety  of  bridge-work  is  that  of 
a  portion  of  the  body  of  a  bridge  extending  beyond  an  abutment,  and 
having  attachment  at  but  a  single  point.  It  will  be  seen  that  there  is 
involved  a  faulty  and,  it  may  be,  a  vicious  mechanical  principle.  It  is  a 
variety  of  structure  which  has  no  counterpart  in  bridges  as  the  engineer 
knows  them. 

The  danger  attending  or  following  its  employment  is  mechanical  dis- 
placement of  the  abutment  itself,  the  danger  being  in  the  direct  ratio  of 
the  amount  of  force  received  by  and  through  the  extension,  and  in  the 
inverse  ratio  of  the  number  and  strength  of  the  abutments. 

A  consensus  of  contemporary  opinion  places  these  devices  in  the  cate- 
gory of  abuses  of  bridge-work. 

The  mildest  form  of  the  above  is  seen  in  such  a  fixture  as  Fig,  752. 

Faulty  though  the  design  may  be,  it  cannot  be  denied  that  there  are 
cases  in  which  the  employment  of  the  work  is  justifiable. 

The  force  received  upon  such  a  fixture  as  Fig.  752  necessarily  tends 
to  rotate  the  abutment  crown  or  even  the  root  itself;  the  same  objection 
obtains  with  any  fixture  supported  by  but  one  abutment.  The  details 
of  construction  of  such  a  piece  and  of  Fig.  751  are  evident. 

Fig.  731  Fig.  7c? 


Figs.  753-755  (after  Dr=  Parr)  exhibit  a  case  in  which  the  exten- 
sive work  figured  has  its  justification  in  the  advantages  afforded  by 
such  a  piece  over  a  plate  denture,  so  long  as  the  abutments  maintain 
their  fixation.  It  is  to  be  recognized  that  this,  as  in  other  extreme  cases 
of  bridge- work,  is  governed  by  matters  of  economy. 

It  is  necessarily  doubtful  how  long  the  abutments  will  persist  in  a 
condition  of  secure  fixation,  so  that  the  question  concerns  the  purse  of 
the  wearer :  can  he  afford  (financially)  to  pay  the  fee  for  such  an  appli- 
ance for  the  term  of  service  it  is  likely  to  afford  him  ? 

The  proper  construction  and  adaptation  of  such  pieces  tax  to  the 
utmost  the  skill,  knowledge,  and  ingenuity  of  the  expert  mechanic; 
the  no\'ice  is  ^^'ise  in  avoiding  them. 

The  figures  illustrate  the  most  extensive  apparatus  anchored  to  abut- 
ments which  dental  literature  records.  The  crowns  and  dummies  of 
such  cases  are  constructed  after  the  methods  described.  Oval  plates 
of  gold  are  swaged  to  cover  a  greater  area  of  the  ridge  than  embraced 
by  the  base  of  the  teeth  they  are  to  support.  Upon  them  plate  teeth  or 
all-gold  cro^Tis  mav  be  fitted,  and  attached  to  the  terminal  dummies. 


744 


AN  ASSEMBLAGE  OF  UNITED  CROWNS. 


REMOVABLE   BRIDGES. 


These  are  devices  which  are  so  attached  to  abutments  that  they  may 
be  removed  by  the  operator  for  the  purpose  of  repair  or  to  gain  access 
to  abutments  which  might  possibly  retjuire  therapeutic  aid;  again,  as  a 
means  of  bridging  spaces  to  whicli,  owing  to  the  position  of  the  abut- 
ments, it  would  be  impracticable  to  properly  adapt  fixed  bridges.  Others 


are  designed  and  attached  so  that  the  patient  may  remove  them  for  hy- 
gienic considerations. 

The  first  consideration  is  the  perfect  protection  of  the  abutments 
themselves  against  the  entrance  of  fermentable  material,  otherwise  the 
spaces  existing  between  the  abutment,  crowns,  and  these  bases  them- 


FiG.  754 


Fig.    755 


selves  would,  by  being  accessible  to  the  causes  of  dental  caries,  bring 
about  the  dissolution  of  the  abutments. 

In  devising  this  variety  of  bridge  or  in  applying  devices  it  is  prefer- 
able to  select  those  whose  mode  of  retention  and  method  of  construction 
are  simple. 

The  means  of  anchorage  of  this  variety  of  bridge-work  is  either 
through  telescoping  barrels;    posts  fitting  in  sockets  anchored   in   the 


REMOVABLE  BRIDGES. 


745 


roots  of  teeth;  attachment  by  means  of  screw  sockets  in  prepared  abut- 
ments; by  variously  shaped  sockets  in  the  body  of  the  bridge  or  attached 
to  the  abutment  crowns,  in  which  closely-fitting  posts  are  sHpped.  Their 
degrees  of  simphcity  are  in  the  order  named. 

With  the  advent  of  removable  bridges,  the  possibilities  of  bridge 
work  have  been  greatly  increased.  In  many  cases  where  it  would  be 
inexpedient  to  put  a  fixed  bridge,  a  perfectly  satisfactory  and  lasting 
removable  bridge  may  be  placed.  This  is  true  for  instance  of  the  lower 
jaw  where  all  of  the  molars  have  been  lost.  These  teeth  may  be  re- 
stored by  the  use  of  removable  extension  saddles,  a  restitution  not  to 
be  thought  of  by  means  of  fixed  bridge- work. 

Fig.  756 


Aside  from  the  enlargement  of  the  field  of  usefulness,  there  are  many 
points  of  superiority  of  removable  over  fixed  bridge-work  and  one  of 
the  most  important  of  these,  is  its  hygenic  character.  It  is  absolutely 
impossible  to  thoroughly  cleanse  and  sterilize  a  bridge  which  is  per- 
manently fixed  in  the  mouth.  There  will  be  portions  of  it  which  can- 
not be  reached  with  the  tooth-brush,  and  any  antiseptic  solution  which 
would  be  strong  enough  to  disinfect  it  perfectly  would  be  injurious  to 
the  mucous  membrane.  In  the  case  of  a  removable  bridge,  however, 
it  may  be  taken  from  the  mouth  in  a  moment  and  sterilized  by  boil- 
ing, or  cleansed  by  other  approved  means  which  the  patient  is  capable 
of  using.  The  inner  abutments  are  then  easy  of  access,  and  being 
perfectly  smooth  on  all  sides  may  be  cleansed  with  very  little  trouble 
before  the  bridge  is  replaced. 


r46 


.l.V  ASSEMBLAGE  OF  VXITED  CliOWXS. 


Another  point  in  favor  of  removable  work,  is  the  ease  with  which  it 
may  be  repaired  in  case  of  accident.  After  many  of  the  accidents 
which  happen  to  a  bridge,  it  is  necessary  to  remove  it  in  order  to  repair 
it,  and  if  the  piece  be  fixed,  it  will  be  more  or  less  injured  in  its  removal 
from  the  mouth  and  the  removal  itself  will  be  a  matter  of  considerable 
difficulty.  In  a  large  piece  where  there  are  several  abutments,  if  one 
becomes  loosened,  in  order  to  re-cement  it, it  would  be  necessary  to  cut 
and  loosen  all  of  the  abutment  pieces  before  the  bridge  could  be  re- 
moved. In  many  instances  the  abutment  tooth  would  be  entirely 
ruined  before  it  was  discovered  that  there  was  anything  the  matter 
with  it  because  the  seat  of  the  difficulty  is  out  of  sight  beneath  the 
bridge.     With  a  removable  piece,  if  one  of  the  abutment  caps  becomes 

Fig.  757 


loose, it  will  be  instantly  discovered  and  may  be  re-cemented  at  once 
without  the  slightest  trouble  or  injury  to  the  bridge. 

Another  and  very  important  consideration  is  the  facility  with  which 
anv  of  the  teeth  adjacent  to  a  removable  bridge  may  be  treated  in  case 
of  accident, decay,  or  other  pathological  condition.  The  bridge  may  be 
taken  out,  the  rubber  dam  put  on  over  the  abutments  and  there  will  be 
ample  room  for  any  operation  without  further  separation. 

The  value  of  removable  bridge-work  depends  entirely  on  the  ac- 
curacy with  which  the  various  details  of  construction  and  adjustment 
are  done.  The  fitting  of  the  several  portions  of  the  bridge  to  the  abut- 
ments must  be  as  nearly  perfect  as  possible  or  the  work  cannot  be  sat- 
isfactorv. 

The  first  of  these  devices  was  that  of  Dr.  R.  W.  Starr' (Fig.  756.) 
The  abutment  teeth  were  trimmed  to  a  form  Avhich  permitted  the  ad- 
justment of  ferrules  which  were  cemented  to  their  bases. 

*     The  Dental  Cosmos   Vol.  xx^'iii,  p.  18. 


REMO  VA  n I. E  BRIDCIE. 


747 


Telescoping  barrels,  with  properly  occluding  caps,  are  fitted  over 
these,  being  cut  away  at  such  asi)ects  as  would  pre^'ent  their  })lacement 
in  a  common  piece.  A  tlummy  crown  is  fitted  between  and  attached  to 
tliem.     The  pieces  were  set  with  gutta-percha. 

The  same  principle  is  applied  in  Figs.  7G0-762. 


Fig.  75S 


Fig.  759 


The  illustrations  explain  in  themselves  the  methods  and  steps  of  the 
construction. 

Another  method  of  applying  a  removable  bridge  to  simliar  cases  is 
that  of  Dr.  R.  B.  Winder.  Collars  are  fitted  to  the  abutments,  to  which 
perfectly  flat  caps  are  soldered.  A  bite  and  impression  are  taken  in 
which  the  caps  are  withdrawn.     Occluding  caps  are  formed,  w^hich  are 


Fi6.  760 


Fig.  761 


/% 


0    w 


filled  flush  with  solder  and  ground  flat  to  fit  the  ferrule  tops.  Dummies 
are  constructed  and  united  to  one  another.  The  caps  are  to  be  attached 
either  by  screws  passing  into  the  crowns  of  the  abutments  .or  else  by 
nuts  passing  over  screws  which  have  been  attached  to  the  ferrule  tops, 
over  which  the  occluding  cap  is  set,  being  perforated  for  the  passage  of 
the  screws.     It  is  advised  that  the  pieces  be  now  placed  in  position  in 

Fig.  762 


the  mouth,  held  together  by  means  of  adhesive  wax.  Over  the  pieces 
sufficient  investing  material  is  placed  to  hold  them  together;  they  are 
then  encased  in  investment  and  the  caps  attached  to  the  dummy  block. 
Holes  may  be  drilled  through  the  deepest  part  of  the  cap  large 
enough  to  admit  the  screws,  and  continued  into  the  crowns  as  deep  as 


-48 


AN  ASSEMBLAGE  OF  UNITED  CROWNS. 


the  screws  are  long.  The  holes  in  the  crowns  may  be  enlarged  and  the 
screws  slightly  oiled.  Zinc  phosphate  is  placed  in  the  pits,  the  l^ridge 
is  set  in  position,  and  the  screws  thrust  in  to  the  cement  while  the  latter 
is  still  soft. 

These  forms  of  bridges  are  applicable  where  the  abutment  teeth 

Fig. 763 


incline  toward  one  another  at  such  an  angle  as  to  render  the  placing 
of  complete  cylinders  impracticable  or  impossible.  The  more  general 
employment  of  the  same  or  similar  methods  in  many  of  the  cases  which 
receive  fixed  bridges  would  remove  many  of  the  objections  urged  against 
the  latter. 

Fig.  764 


An  applicable  and  well-devised  appliance  is  shown  in  Fig.  763/ in 
which  fixation  of  the  bridge  to  the  abutments  is  secured  by  means  of  a 
telescoping  collar  placed  over  a  capped  root,  its  other  extremity  having 
a  socket  fitted  to  and  slipped  over  a  retaining  shoulder. 


1  Dr.  C.  L.  Alexander. 


ABUTMEXTS.  749 

A  bridge  heltl  by  two  similar  shoulders,  but  removal)le  outwardly, 
is  shown  in  Fig.  791:  it  is  designed  to  overcome  the  tendency  to  dis- 
placement by  the  stress  of  mastication  present  in  those  devices  which 
are  inserted  vertically. 

Dr.  Parr's  method  of  constructing  these  telescoping  ends  is  by  far 
the  simplest  ottered.  Two  pieces  of  platinum  plate  are  shaped  as  in 
Fig.  765,  so  that  one  shall  telescope  the  other:  the  inner  one  is  filled 
flush  with  wax  and  invested;  the  wax  is  removed,  the  space  is  filled  by 
melting  gold  plate  i:i  it.  The  outer  section  is  filled  with  invest- 
ment and  its  walls  are  made  rigid  by  flowing  gold  over  them,  or,  what 
is  preferable,  adding  thick  pieces  of  plate  to  each  side  and  joining  them 
by  means  of  22-carat  solder.  The  shoulders  are  soldered  to  the 
crowns,  the  slots  are  adjusted  to  the  shoulders,  their  ends  attached  to 
the  stays  of  the  dummies.  It  is  necessary  that  the  slots  should  be 
immovably  held  against  the  stays  to  ensure  their  correct  position  in 
the  finished  piece.  Soft  adhesive  wax  is 
placed  around  them,  attaching  them  to  ^^'^-  '^s 

the  backings,  an  unusually  large  amount 
of  the  wax  being  used.  The  piece  is  chilled 
and  the  dummies  and  sockets  with- 
drawn. If  both  sockets  come  away 
without  detachment,  the  piece  is  imme- 
diately invested;  if  one  or  both  have 
broken  away,  the  sharp  line  of  fracture 
of  the  brittle  cement  furnishes  the  guide  for  their  accurate  replacement. 

The  writer  adx-ises  that  the  free  ends  of  the  shoulder-piece  be  left  as 
extensions  which  are  adapted  to  the  wall  of  the  abutment  crown,  the 
socket  piece  to  have  similar  wings  which  shall  outhne  the  terminal  wall 
of  the  brido-e  bodv  in  its  finished  state. 


ABUTMENTS. 

Of  the  different  styles  of  abutments  which  may  be  utilized  in  remov- 
able bridge-work,  the  telescope  crown  is  probably  the  one  most  fre- 
quently indicated.  The  telescope  crown  should  not  be  confounded 
with  the  shell  crown.  The  shell,  or  full  gold  crown  simply  covers  the 
tooth  or  root  and  is  used  as  a  single  crown,  or  as  an  abutment  in  fixed 
bridge-v\-ork.  In  the  telescope  crown,  there  are  two  caps,  one  tele- 
scoping and  fitting  the  other  as  exactly  as  the  tubes  or  slides  of  a  tele- 
scope, the  inner  cap  of  which  is  cemented  to  the  tooth  serving  as  an 
abutment.  This  crown  is  only  used  in  removable  bridge-work.  It  is 
indicated  for  molars  and  bicuspids  where  a  full  gold  crown  can  be  used, 
but  should  never  be  employed  in  the  front  of  the  mouth.  The  tooth  for 
the  reception  of  a  telescope  crown  should  be  prepared  in  exactly  the 
same  way  as  for  a  full  gold  crown,  with,  the  exception  that  a  little  more 
of  the  tooth  structure  should  be  ground  away  from  the  occlusal  surface. 
The  sides  should  be  trimmed  so  that  the  tooth  is  very  slightly  conical, 


oO 


AX  ASSEMBLAGE  OF  UXITED  CliOWXS. 


its  greatest  circumference  being  about  one  sixteenth  of  an  inch  l)elow 
the  gum  hne. 

It  is  not  desirable  that  the  abutments  should  be  exactly  parallel,  but 
they  should  be  very  nearly  so.  Advantage  should  be  taken  of  the 
natural  inclination  of  the  teeth.  If  they  are  diverging,  they  should  be 
ground  so  that  when  the  bridge  is  put  in  place,  the  teeth  will  be  drawn 
together  slightly  and  spring  back  as  it  is  pressed  home.  If  the  teeth 
converge  they  will  be  forced  a  little  apart.  This  slight  natural  spring 
of  the  teeth  will  assist  in  holding  the  bridge  firmly  in  place,  but  it  must 
be  very  slight,  otherwise  the  removal  and  replacing  of  the  bridge  would 
have  a  tendency  to  loosen  the  roots. 

The  telescope  crown  should  be  made  of  coin  gold,  or  some  very  hard 
alloy  of  that  metal.  The  regular  tweniy-two  carat  plate  as  purchased 
at  the  dental  depots  is  too  soft  to  withstand  the  strain  and  wear  to  which 
it  will  be  subjected.  If  the  telescope  crown  be  accurately  made  of  a 
rigid  material  like  coin  gold,  there  will  be  practically  no  wear  on  it, even 
after  years  of  use.     The  fluids  of  the  mouth  seem  to  form  a  coating 


ri.;.766 


Fig.  707 


which  prevents  the  actual  contact  of  the  metal  in  the  two  caps,  however 
closely  they  may  fit, but  if  the  material  of  which  the  bands  are  made  be 
so  soft  as  to  allow  of  their  stretching  in  the  slightest  degree,  this  would 
render  the  piece  worthless  in  a  comparatively  short  time. 

The  band  of  coin  gold  No.  .30  gauge  is  made  to  conform  to  the  tooth, 
the  sides  being  nearly  parallel,  or  slightly  diverging  toward  the  neck, 
and  it  is  festooned  to  follow  the  gum  line  so  that  it  will  go  an  ecjual  dis- 
tance under  the  free  margin  all  around.  It  is  then  cut  off  even  with 
the  top  of  the  stump  and  filed  perfectly  flat  and  a  floor  of  No.  28  coin 
gold  is  sweated  to  it.  In  sweating  the  floor  to  the  band,  the  former  is 
first  flattened  so  that  there  will  be  close  contact  between  it  and  the  band 
all  around.  It  is  then  fluxed  and  held  by  one  corner  in  a  pair  of  finely 
pointed  pliers  over  a  Bunsen  flame  until  the  parts  are  united.  The 
surplus  gold  of  the  floor  is  then  trimmed  away  and  the  sides  of  the  cap 
polished.  We  now  have  what  is  practically  a  seamless  crown  and  are 
ready  to  make  the  outer  cap.  As  a  first  step,  the  inside  of  the  cap  is 
given  a  very  thin  coating  of  melted  wax  to  prevent  its  union  with  the 


TELESCOPE  CROWN.  751 

fusible  metal  which  is  to  be  poured  in  it.  It  is  then  pushed  into  a 
paper  tube,  which  can  be  made  by  rolling  a  piece  of  paper  around  a  lead 
pencil  or  stick  of  suitable  size,  held  together  with  a  small  gum  elastic 
band,  and  the  cap  and  the  tube  filled  with  fusible  metal.  (Fig.  766.) 
This  renders  the  cap  perfectly  solid  so  that  it  is  impossible  to  crush  it.  A 
new  measurement  is  taken  at  about  the  middle  of  the  cap  and  the  gold 
for  the  outer  band  is  cut  a  little  shorter  than  the  measurement  and  slightly 
tapering,  so  that  the  band  will  be  a  little  larger  toward  the  neck,  and  its 
ends  sweated  together. 

It  is  festooned  to  follow  the  lower  edge  of  the  inner  cap  and  forcibly 
driven  x>\ev  it  to  within  about  one-sixteenth  of  an  inch  of  this  edge. 
(Fig.  767.) 

The  band  is  then  cut  le\'el  with  the  floor  of  the  inner  cap  and  filed 
flush  with  it.  It  is  then  removed  and  a  floor  of  No.  30  coin  gold  is 
sweated  to  it.  The  extending  edges  of  the  floor  are  then  trimmed 
flush  with  the  sides  of  the  band  and  it  is  ready  for  the  contour. 

This  is  made  by  building  it  on  the  outside  of  the  band.  A  piece  of 
No.  28  coin  gold  is  cut,  its  width  being  about  the  same  as  the  width  of 
the  outer  band  and  its  length  about  twice  the  diameter  of  the  cap. 

Fig.  768  Fig.  769  Fig.  770  Fig.  771  Fig.  772 


(Fig.  768.)  The  lower  edge  of  this  is  then  bent  slightly  inward  as  it  is 
desirable  that  the  solder  used  should  not  unite  the  piece  all  the  way  up 
the  band,  but  should  catch  it  only  at  the  extreme  edge  as  in  Fig.  769. 
The  contour  piece  is  then  placed  on  the  band,  the  lower  edge  coming 
only  about  one-thirty-second  of  an  inch  from  the  lower  edge  of  the  band, 
fluxed  and  soldered  with  a  very  small  piece  of  22-carat  solder  (Fig.  770), 
using  the  small  blue  point  of  the  blowpipe-flame.  It  is  then  cleansed 
in  acid  and  another  piece  attached  to  the  opposite  side  in  the  same 
manner.  These  contour  pieces  are  always  attached  to  the  mesial  and 
distal  sides  of  the  cap.  The  cap  with  the  wangs  attached  is  placed  on 
the  inner  cap  and_the  wings  thrown  out  to  the  desired  angle,  as  in  Fig. 
771,  and  the  ends  turned  in  at  the  buccal  and  lingual  side  .so  as  to  give 
a  natural  contour  to  the  crown.  (Fig.  772.)  The  crown  is  then  well 
fluxed  between  the  contour  pieces  and  the  band  and  along  the  edges  of 
the  wings  and  the  whole  soldered  with  22-carat  solder,  partly  filling  the 
space  between  the  ^^ings  and  the  band. 

This  is  done  by  laying  the  crown  on  a  charcoal  block  and  placing 
the  pieces  of  solder  on  the  buccal  and  lingual  sides  between  the  ends  of 
the  two  plates  (Fig.  773),  and  drawing  it  down  on  each  side  with  the 
small  flame  of  the  blow^^ipe.  The  surplus  gold  of  the  contour  is  then 
cut  away  and  the  contour  flled  flush  with  the  floor  of  the  cap.  A  suit- 
able cusp  is  then  made,  and  its  under  surface  filed  flat  to  fit  the  top  of 


752 


AN  ASSEMBLAGE  OF   UNITED  CROWNS. 


the  cap.  The  cusp  and  cap  are  then  fluxed,  wired  together  anfl  sol- 
dered with  2()-carat  solder,  laying  the  crown  on  its  side  on  a  charcoal 
l)lock,  the  piece  of  solder  on  the  band  in  contact  with  the  cusp  and  sol- 
dering with  the  small  flame  of  the  blowpipe.     (Fig.  774.) 

Where  the  teeth  are  short  or  where  there  is  to  be  but  one  retaining 
abutment,  a  combination  of  the  telescope  cap  with  a  tube  and  split  pin 
forms  a  most  excellent  attachment.  The  inner  band  is  made  as  for  the 
regular  telescope  crown.  A  hole  is  then  made  in  its  floor  and  a  tube  set 
in,  resting  on  the  floor  of  the  pulp  chamber  and  waxed  firmly  in  place. 
(Fig.  775.)     In  adjusting  the  tube,  care  must  be  used  to  have  its  long 


Fig.  773 


Fig.  775 


axis  exactly  parallel  with  the  sides  of  the  band.  The  cap  is  then  filled 
with  investment  and  the  tube  soldered  in  place  with  20-carat  solder. 
The  tube  is  now  cut  off  flush  with  the  floor  of  the  cap  and  the  cap  pol- 
ished. The  inside  of  the  cap  is  now^  coated  very  thinly  with  wax  and 
it  is  filled  with  fusible  metal  as  already  described. 

The  outer  band  is  made  and  contoured  exactly  the  same  as  for  a  regu- 
lar telescope  crown  and  the  top  filed  perfectly  flat,  and  a  floor  of  No.  30 
coin  gold  sweated  to  it. 

The  position  of  the  opening  of  the  tube  is  a.scertained  by  placing  the 
outer  cap  in  position  on  the  inner  cap  and  with  a  soft  pine  stick  and 
hammer  tapping  the  floor  directly  over  the  mouth  of  the  tube. 


Fig.  776 


Fig. 777 


Fig.  778 


Fig.  779 


© 


When  the  outer  cap  is  removed  the  outline  of  the  hole  will  be  clearly 
defined  on  the  inner  side  of  the  floor  and  may  be  punched  or  drilled 
to  the  proper  size  for  the  reception  of  the  pin.  The  split  pin  is  then 
made  to  fit  the  tube  easily  but  not  loosely,  but  should  fit  the  hole  in  the 
.floor  of  the  outer  cap  tightly  and  be  fastened  to  it  with  hard  wax  while 
the  parts  are  in  position.  The  cap  is  then  removed,  filled  with  invest- 
ment and  the  pin  soldered  to  the  floor  with  a  very  small  piece  of  22-carat 
solder.  The  surplus  pin  is  cut  away  nearly  to  the  floor  of  the  cap. 
(Fig.  776.)  The  cusp  is  then  selected,  the  under  surface  filed  flat  and  a 
hole  drilled  through  it  to  receive  the  part  of  the  pin  which  projects 


KEY  AND  SHOE  ATTACHMENT.  753 

above  the  floor  of  the  cap.  They  are  then  wired  together  and  soldered 
in  the  same  manner  as  the  regular  telescope  crown.  This  attachment 
is  especially  useful  in  molars  or  bicuspids  where  the  crowns  are  very 
short. 

Another  form  of  anchorage  which  has  given  great  satisfaction  is  the 
inlay  attachment.  In  this  style  of  abutment  the  natural  crown  of  the 
tooth  is  preserved  and  it  is  especially  applicable  to  molars.  The  tooth 
is  devitalized  and  cut  out  on  the  occlusal  surface  from  one-third  to  one- 
half  the  length  of  the  crown,  and  down  on  the  mesial  side  far  enough  to 
allow  for  a  heavy  round  bar,  about  No.  13  gauge  and  a  sufficient  thick- 
ness of  gold  to  give  stability  lo  the  inlay.  (Fig.  777,  A  and  B.)  The 
■pulp  chamber  is  then  filled  with  gutta-percha,  the  cavity  being  made 
non-retentive,  leaving  the  sides  curved  or  straight  and  the  bottom 
rounded  or  flat  as  the  operator  desires.  Pure  gold  of  No.  34  or  No.  36 
gauge,  or  inlay  platinum  is  then  burnished  into  it  as  for  an  inlay,  great 
care  being  used  to  have  the  margins  perfect. 

A  hole  is  then  made  near  the  distal  end  of  the  matrix  and  through  the 
gutta  percha  to  the  floor  of  the  pulp  chamber  and  in  it  is  placed  an 
iridio-platinum  tube,  large  enough  to  take  a  pin  of  No.  13  or  14  gauge. 

Fig.  780  Fig.  781  Fig.  782 

1 T        O  A  B 


>i^ 


It  is  then  waxed  in  place  and  the  wax  packed  tightly  in  the  matrix  and 
around  the  tube.  It  is  now  removed,  invested  and  filled  with  coin  or 
pure  gold,  thus  making  a  perfect  inlay  with  a  tube  extending  through  it. 
(Fig.  778.)  A  groove  is  now  cut  from  the  tube  to  the  mesial  end  of  the 
inlay  with  small  round-edged  carborundum  wheels  or  fissure  burs  and 
finished  with  plug  finishing  burs,  of  the  same  size  or  slightly  larger  than 
the  inside  diameter  of  the  tube. 

The  bar  and  pin  are  made  of  platinized  gold  wire  left  open  for  about 
one-quarter  of  an  inch  from  the  end  and  bent  so  that  it  will  go  to  the 
bottom  of  the  tube  and  lie  closely  in  the  bottom  of  the  groove.  Fig. 
779  shows  a  section  of  the  tooth  with  the  inlay  and  tube  in  position 
and  the  bar  and  pin  in  place. 

The  articulation  is  taken  in  plaster  with  the  inlay  in  position  in  the 
tooth,  the  cast  prepared  and  the  bridge  made,  the  bar  being  soldered 
firmly  to  it. 

Another  style  of  abutment,  especially  adapted  to  bicuspids  and  molars 
having  long  crowns,  is  the  dovetailed  key  and  shoe  attachment. 

The  key  is  made  of  iridio-platinum  and  filed  smooth  to  form  a  dove- 
tail as  in  Fig.  780,  A  and  B.  A  strip  of  the  same  metal  No.  32  gauge 
is  bent  to  fit  the  sides  of  the  key  perfectly  and  filed  off  even  with  the 
face  or  broad  side  of  the  key,  and  a  floor  of  the  same  metal  fitted  to  it 
and  soldered  with  a  little  pure  gold.     (Fig.  781',  A  and  B.) 

48 


754 


AN  ASSEMBLAGE  OF  UNITED  CROWNS. 


In  usiiifi;  this  form  of  abutment  the  side  of  the  crown  to  which  the  key 
is  to  he  attached  should  be  straifjht  from  the  fjuni  hue  to  the  top  of  the 
cusp,  and  should  l)e  reinforced  with  a  piece  of  No.  28  gauge  coin  gold 
soldered  across  the  whole  face  of  the  crown.     (Fig.  782,  A  and  B.) 

The  key  is  then  put  in  place,  a  hole  drilled  through  it  and  the  side  of 
the  band,  and  it  is  fastened  with  a  small  platiiuim  rivet,  such  as  a  tooth 
l)in,  the  under  surface  of  the  key  having  first  been  covered  with  pure 

Fig.  784 


Fig.  785 


/^=^T^ 


gold,  as  the  union  between  iridio-platinum  and  the  solder  is  not  strong. 
It  is  then  soldered  to  the  cap,  using  very  little  solder.  (Fig.  783,  A  and 
B.)  The  female  part  of  the  attachment,  or  shoe,  is  then  slipped  over  the 
key  and  a  thin  piece  of  platinum  cut  out  to  slip  down  over  the  key  next  to 
the  crown  and  this  is  burnished  closely  to  it.  (Fig.  784.)  It  is  then 
waxed  to  the  shoe,  removed,  invested,  and  covered  A^th  pure  or  coin 
gold  (Fig.  785),  after  which  it  is  trimmed  to  its  proper  dimensions,  re- 


FiG.  786 


Fig.  787 


li 


placed  on  the  crown,  the  facings  ground  in,  and  the  bridge  con.structed. 
If  a  saddle  is  to  be  used,  it  is  first  waxed  carefully  to  the  shoe,  removed 
and  soldered,  after  which  it  is  replaced  on  the  model  and  the  bridge 
constructed   as  before. 

For  attachments  for  any  of  the  anterior  teeth  or  for  bicuspids,  where 
the  teeth  are  to  be  cut  to  or  below  the  gum  line,  the  cap  with  the  tube 
and  split  pin  will  be  found  to  be  most  generally  useful. 

The  tooth  is  cut  down,  the  band  made  and  fitted  in  the  same  way  as 


REMOVABLE  RICHMOND  CROWN. 


i  iy'o 


for  a  Richmond  crown,  being  carried  about  one-sixteenth  of  an  inch 
iintlor  the  gum,  after  which  it  is  removed  and  the  root  cut  down  just 
below  the  gum  hue  on  the  hibial  side,  but  not  so  low  as  for  a  Richmond 
crown,  and  leaving  it  high  on  the  palatal  or  lingual  side.  For  doing 
this,  the  Ottolengui  root  facers  (Fig.  786),  are  best  adapted  as  they  will 
take  the  root  down  quickly  and  evenly  and  with  less  mutilation  of  the 
gum  tissue  and  consequently  less  pain  to  the  patient. 

The  band  is  then  cut  flush  with  the  top  of  the  stump  and  the  floor 
sweated  or  soldered  to  it. 

In  enlarging  the  canal  of  a  root  to  receive  either  a  pin  or  tube,  spear 
pointed  drills  or  instruments  which  cut  on  the  end  should  never  be  used, 
as  there  is  danger  of  perforating  the  side  of  the  root. 

The  canal  is  first  opened  with  broaches,  these  are  followed  by  Gates- 
Glidden  drills,  beginning  with  the  small  and  working  up  to  the  large 
ones  and  enlarging  the  canal  to  within  about  one-eighth  of  an  inch  of 
the  apex.  These  are  followed  by  the  reamers  which  are  made  in  sizes 
to  coiTespond  to  the  size  of  the  tubes  or  pins  which  are  to  be  used. 
(Fig.   787.)     Both  these  and  the   Gates-Glidden  drills   ha\'e   smooth 

Fig.  788  Fig.  789  Fig.  790  Fig.  791  Fig.  792 


guide  points  which  will  follow  a  canal,  but  will  not  cut  on  the  end  and 
there  is  very  little  danger  of  perforating  a  root  in  using  them. 

The  canal  having  been  enlarged  to  the  proper  size,  a  hole  is  made  in 
the  floor  of  the  cap  which  is  placed  on  the  root,  the  tube  adjusted  and 
waxed  to  it  with  sticky  wax.  (Fig,  788.)  It  is  then  removed  with  the 
cap,  invested  and  soldered  the  same  as  a  pin  in  a  Richmond  crown. 

After  it  is  soldered,  the  tube  is  cut  off  flush  with  the  floor  of  the  cap 
and  the  cap  polished,  care  being  used  not  to  round  the  corners  f^Fig. 
789.) 

The  cap  is  then  placed  on  the  root  and  the  impression  taken  and  cast 
made.     The  subsequent  steps  are  done  on  the  cast. 

The  floor  of  the  outer  cap  is  made  of  No.  28  coin  gold,  a  hole  being 
drilled  through  a  piece  of  proper  size  for  the  case  so  that  the  pin,  \Yhich 
has  been  previously  fitted  to  the  tube,  will  fit  tightly.  They  are  then 
placed  in  position  on  the  inner  cap,  waxed  together,  removed  and  sol- 
dered with  a  very  small  piece  of  22-carat  solder.  (Fig.  790.)  The  pin 
and  floor  are  then  cleansed  in  acid,  replaced  on  the  inner  cap  and  the 
floor  trimmed  flush  with  it  all  round. 

A  half  band  is  of  No.  28  coin  gold  and  should  extend  about  half  way 
to  the  buccal  side  of  the  floor  as  in  (Fig.  791.)  It  should  extend  only 
to  the  gum  line  on  the  lingual  side  and  should  not  go  below  it.     It  is 


7'j(3 


AN  ASSEMBLAGE  OF  UNITED  CROWNS. 


then  waxed  to  the  outer  floor,  removed  and  soldered,  using  a  very  little 
22-earat  solder. 

Another  way  of  making  a  tube  and  split  pin  attachment  which 
is  especially  useful  in  cases  where  the  roots  stand  at  such  an  angle  that 
it  is  not  possible  to  insert  the  tubes  to  a  sufficient  depth  and  have  them 
parallel,  is  to  have  the  split  pin  attached  to  the  lower  or  inner  cap  and 
the  tube  imbedded  in  the  bridge.  Take  for  example  two  canine  roots 
in  the  lower  jaw,  standing  as  represented  in  Fig.  792. 

In  a  case  of  this  description,  the  roots  are  prepared  in  the  same  way 
as  when  they  stand  in  a  normal  position,  with  the  exception  that  the 
mesial  or  approximal  angle  is  cut  away,  in  order  that  the  bands  may  be 


Fig.  793 


Fig.   794 


adjusted  with  their  sides  nearly  parallel  to  each  other.  The  bands  are 
then  fitted,  the  roots  cut  down,  the  canals  enlarged  to  receive  a  strong 
pin  and  a  plaster  impression  taken  with  the  bands  and  pins  in  position 
as  in  Fig.  793.  A  cast  is  then  made,  the  bands  cut  flush  with  the  top 
of  the  stump  and  the  floor  of  No.  28  gauge  coin  gold  is  sweated  to  them. 
An  opening  is  then  made  through  the  floor  to  fit  the  pins  tightly  and  the 
pins  are  bent  just  beneath  the  floor  so  that  when  they  pass  through 
they  will  be  parallel  with  each  other  or  nearly  so.  (Fig.  794.)  They 
are  then  waxed  together  invested  and  soldered  from  the  under  side. 

In  making  the  outer  cap  the  floor  of  No.  28  gauge  coin  gold  is  drilled 
so  as  to  fit  the  pin  easily  but  not  loosely.  It  is  then  cut  flush  with  the  sides 


Fig.  795 


Fig.   796 


of  the  inner  cap  and  the  half  band  made  and  soldered  to  it,  after  which 
it  is  replaced  on  the  inner  cap.  The  tube  is  next  placed  over  the  pin 
and  is  made  to  set  down  closely  on  the  floor  all  around  and  is  waxed  to 
it  with  hard  tough  wax.  It  is  then  removed,  a  little  investing  material 
carried  into  the  tube  and  a  small  iron  wire  inserted,  letting  it  extend 
about  one  (piarter  of  an  inch  below  the  floor.  (Fig.  795.)  This  will 
hold  the  tube  in  position  and  is  imbedded  in  the  investment,  the  tube 
being  soldered  to  the  floor  with  22-carat  solder.  (Fig.  796.)  The  facing 
is  then  ground  to  the  floor  of  this  cap  and  when  the  bridge  is  invested 
for  soldering,  a  small  iron  wire  is  inserted  in  the  investment  to  pre- 
vent the  tube  from  shifting,  the  same  as  when  attaching  it  to  the  floor. 


COUXTERSUXK  SUPPORTIXG  ABUTMEXTS.  757 

The  abutments  which  liave  been  described  are  all  known  as  retain- 
ing abutments.  By  retaming  abutment  is  meant  one  wJiich  holds  the 
bridge  firmly  in  place  in  the  mouth,  preventing  its  shifting  or  dropping 
out,  such  as  a  telescope  cap,  tube  and  split  pin,  etc. 

A  supporting  abutment  is  one  which  supports  one  end  of  a  bridge, 
but  has  nothing  to  do  with  retaining  the  piece  in  the  mouth.  A  coun- 
tersunk gold  filling  in  which  a  spur  rests  is  an  example  of  this  latter 
style. 

Countersunk  Supporting  Abutments.— A  hookM  spur  resting  in  a  coun- 
ter sunk  gold  filling  forms  a  most  excellent  support  for  one  end  of 
a  bridge.  This  is  especially  the  case  in  the  lower  jaw,  where  it  will 
safely  support  a  bridge  of  two  or  three,  or  even  more  teeth  with  but  one 

Fig.  79S 


retaining  abutment.  In  the  upper  jaw,  with  a  crown  carrying  a  single 
dummy,  the  other  end  may  be  supported  by  the  counter  sunk  filling, 
and  it  is  often  useful  in  furnishing  additional  support  for  a  larger  bridge 
with  more  than  one  retaining  abutment. 

Where  a  spur  is  to  rest  in  a  filling  in  any  of  the  anterior  teeth  either 
upper  or  lower,  the  cavity  is  made  in  the  palatal  or  lingual  side  of  the 
tojth  toward  the  bridge  as  in  Fig.  797,  A  and  B.  Where  the  bite  does 
not  interfere  the  cavity  is  made  at  me  basilar  ridge  where  the  enamel 
is  very  thick,  and  should  be  of  good  size,  approximately  about  one- 
eighth  of  an  inch  in  diameter.  It  is  best  to  start  it  with  a  small 
carborundum  w^heel,  using  plenty  of  water,  And  cut  through  the  enamel 

Fig.  800  .  Fig.   801  Fia   802 


and  give  the  general  outline  to  the  cavity  before  putting  on  the  rub- 
ber dam.  The  rubber  dam  having  been  adjusted,  the  ca^^ty  is  deep- 
ened with  burs  as  much  as  possible  without  endangering  the  pulp. 
The  cavity  is  well  undercut  and  a  filHng  of  hard  gold  thoroughly 
condensed  is  inserted.  It  is  made"  large  enough  so  that  the  contour  of 
the  tooth  is  som_ewhat  exaggerated  as  in  Fig.  798.  The  filling  is  then 
polished  and  a  hole  drilled  in  the  centre  of  it  on  the  palatal  side  to  wdthin 
a  short  distance  of  the  bottom  of  the  cavity,  the  base  of  the  hole  being 
shaped  \\dth  a  bud  shaped  bur  about  the  size  of  No.  14  to  16  gauge  ware. 
A  groove  the  same  size  is  then  cut  from  this  opening  to  the  distal  side 
of  the  filling,  being  careful  to  leave  a  strong  body  of  gold  underneath  so 
as  not  to  weaken  the  filling.     (Fig.  799)  A  and  B. 


758  AN  ASSEMBLAGE  OF  UNITED  CROWNS. 

The  spur  is  made  of  iridio-platinum  or  platinized  gold  wire  of  Xo.  14 
to  10  gauge,  the  size  dependiug  upon  the  size  of  the  bridge  and  the 
amount  of  strain  to  which  it  will  be  subjected.  The  end  of  the  wire  is 
bent  at  right  angles  and  pointed,  leaving  it  just  long  enough  to  rest  on 
the  bottom  of  the  hole  with  the  shank  resting  in  the  bottom  of  the  groove 
(Fig.  800),  and  passing  under  the  cusp  of  the  dummy  or  to  tKe  backing 
of  the  facing,  should  it  be  one  of  the  six  anterior  teeth. 

In  the  molars  or  bicuspids,  the  cavity  is  made  in  the  crown  of  the 
tooth,  extending  dow'n  on  the  approximal  side  far  enough  to  allow  for 
the  filling  and  spur.  (Fig.  801.)  The  inside  base  of  the  cavity  should 
be  made,  as  far  as  possible,  flat  or  slightly  convex  as  in  (Fig.  802.) 
This  will  make  a  firm  base  for  the  filling  and  there  is  little  likelihood 
of  the  tooth  being  fractured  or  split  by  any  pressure  that  may  be  brought 
to  bear  on  it,  the  shape  of  the  filling  having  a  tendency  to  bind  the  crown 
together  and  prevent  fracturing. 

If  the  cavity  is  prepared  so  that  the  filling  is  wedge-shaped,  there  is  a 
chance  of  its  splitting  the  tooth,  especially  the  bicuspids  which  are  not 
strong  on  this  line. 

TUBES  AND  SPLIT  PINS. 

The  tubes  for  removable  bridge-work  are  made  from  iridio-platinum 
plate.  No.  32  gauge.  A  series  of  polished  steel  mandrels  of  different 
sizes,  ranging  from  about  No.  13  to  No.  15  Browne  and  Sharpe's  gauge 
are  used. 

The  size  of  the  tooth  must  govern  the  size  of  the  tube  to  be  used,  the 
smaller  size  for  teeth  having  small  roots  and  the  larger  size  for  the  teeth 
with  heavier  roots.  A  strip  of  No.  32  iridio-platinum  plate  is  beveled 
at  the  end  to  a  knife  edge;  the  edge  is  then  turned  slightly  and  rolled 
around  the  mandrel  which  should  be  one  size  smaller  than  the  one  which 
is  to  be  used  in  finishing  the  tube.     (Fig.  803.)     The  mandrel  is  then 

Fig.  803  Fig.  804  Fig.  805 


removed  and  the  tube  soldered  with  pure  gold.  The  next  size  larger 
mandrel  is  then  driven  through  the  tube,  stretching  it  and  making  it 
perfectly  smooth  and  straight  on  the  inside.  The  surplus  plate  is 
now  cut  away  and  the  lap  joint  filed  even  with  the  rest  of  the  tube. 

A  floor  of  the  same  metal  is  then  soldered  to  one  end  of  the  tube 
with  pure  gold  and  the  surplus  trimmed  away  and  the  end  finished 
with  a  file. 

Split  Pins. — In  making  the  split  pins  for  removable  work  half-round 
platinized  gold  wire  is  used.  A  i)iece  of  such  length,  that  when  doubled 
it  will  be  about  one-eighth  of  an  inch  longer  than  the  tube,  is  bent  at  the 
centre  and  the  two  flat  sides  brought  together  and  soldered  just  at 
the  ends  with  coin  or  pure  gold.     (Fig.  804.)     This  end  is  then  grasped 


SADDLE  BRIDGES.  759 

in  a  pin  vise  and  the  pin  filed  to  fit  the  tube.  If  it  is  a  very  long  pin 
it  is  left  closed  at  the  end,  and  to  tighten  it  a  very  thin  instrument  is 
introduced  between  the  halves,  si)rcading  them  slightly,  thus  making 
a  long,  slender  elliptic  spring.  (Fig.  805.)  If  it  is  to  be  a  short  pin, 
the  closed  end  is  cut  ott"  with  a  file  so  that  the  fit  of  the  pin  to  the  tube 
may  be  tightened  by  separating  the  ends  of  the  former  with  a  knife. 
In  a  split  pin  made  in  this  way,  there  is  no  loss  of  material  and  the 
maximum  strength  of  the  metal  is  maintained. 

SADDLE  BRIDGES. 

The  most  difficult  piece  of  work  which  the  crown  and  bridge  special- 
ist may  be  called  upon  to  do,  is  to  make  a  satisfactory  extension  saddle 
bridge  for  the  lower  jaw  restoring  the  lost  molars. 

The  success  of  a  bridge  of  this  kind  depends  entirely  upon  the  per- 
fect adaptation   of   the  saddle  to   the   ridge.     In 
getting  the  impression  for  the  saddle,  it  is  a  good  ^^°-  ^°^ 

plan  to  first  take  an  impression  in  modelling  com- 
position and  after  enlarging  it  a  little  so  that  it  will 
set  further  down  on  the  ridge,  to  use  it  as  a  tray 
for  taking  the  plaster  impression.  A  good  im- 
pression having  been  secured,  the  cast  is  prepared 
and  shoul  i  be  of  sufficient  depth  that  there  will  be 
no  chance  of  the  die  springing  or  breaking  when 
swaging  the  saddle.  The  outline  of  the  saddle  is 
then  marked  on  the  cast  and  the  cast  built  up  a  little  with  wax  around 
theoutline  as  in  Fig.  806,  A  and  B,  so  as  to  turn  the  edge  of  the  saddle 
and  present  a  thick  rounded  edge  to  the  soft  tissues.  The  die  and 
counter-die  may  be  made  of  zinc  and  lead  or  of  fusible  metal,  the 
latter  being  preferable  because  of  its  lack  of  contraction. 

The  saddle  is  struck  up  of  soft  platinum  of  No.  30  or  No.  32 
gauge  and  should  be  just   large  enough  to  allow  for  the  edge  being 

Fig  SO"  Fig.   SOS  Fig.    809 


^\ 


A 


turned  up  all  around.  (Fig.  807.)  It  is  then  cleansed  in  acid,  the 
under  side  painted  with  whiting  to  keep  the  gold  from  running  over 
it,  and  coin  gold  flowed  over  the  sides  so  as  to  fill  them  even  with  the 
turned  up  edges  of  the  plate.  (Fig.  808.)  It  is  then  swaged  again 
with  the  die  and  counter-die,  cleansed  in  acid  and  is  ready  for  ad- 
justment. The  teeth  which  are  to  serve  as  abutments  having  been 
prepared,  the  inner  caps  are  made  and  placed  in  position.  The  next 
step  is  the  one  upon  which  the  success  of  this  form  of  denture  entirely 
depends,  and  that  is  the  one  of  adjusting  the  saddle  accurately  to  the 
alveolar  ridge. 


700 


^.V  ASSEMBLAGE  OF  UNITED  CROWNS 


The  Adjustment  of  the  Saddle  to  the  Ridge.— It  will  he  found  when 
the  saddle  is  placed  in  the  mouth  that  it  is  resting  on  the  top  of  the  ridge 
and  has  no  bearing  anywhere  else.     (Fig.  809.) 

If  this  is  not  remedied,  absorption  will  rapidly  take  place,  allowing 
the  piece  to  sag  and  bringing  the  whole  strain  on  the  abutments,  with 
the  result  that  sooner  or  later  the  roots  will  become  loosened  and  lost. 
The  saddle  is  placed  in  the  mouth  with  the  forefinger  of  each  hand 
resting  on  the  sides  of  the  saddle,  Fig.  809,  and  rocked  from  side  to  side. 
This  will  give  an  idea  as  to  the  amount  of  correction  needed.  It  is 
then  removed  and  grasped  with  the  thumbs  and  forefingers  and  the 
sides  bent  together  a  little,  then  replaced  in  the  mouth  and  tried  again. 
This  is  repeated  until  the  saddle  rests  perfectly  solidly  without  rock- 
ing at  all  and  sets  comfortably  on  the  ridge. 

When  it  is  satisfactorily  adjusted  it  is  held  in  place  with  the  thumb 
and  forefinger  and  it  and  the  abutments  covered  thickly  with  plaster, 
covering  the  finger  as  well,  and  the  saddle  held  firmly  in  position  until 
the  plaster  hardens.     It  is  then  removed  together  with  the  inner  caps 


Fig.  810 


Fig.  SI  1 


Fig.  812 


Fig.  813 


and  all  are  replaced  in  the  impression,  waxed  in  position,  also  waxing 
the  inside  of  the  caps,  and  a  small  cast  run. 

The  inner  caps  are  then  removed  with  warm  pliers  and  the  outer  or 
telescope  caps  are  made,  after  which  the  parts  are  replaced  on  the  cast 
and  the  saddle  waxed  to  the  outer  caps.  The  whole  is  then  removed, 
the  inner  caps  taken  away  and  the  piece  invested  and  the  caps  and 
saddle  united  with  21 -or  22-carat  solder.  After  cleansing  in  acid,  the 
caps  and  saddle  are  placed  in  the  proper  position  in  the  mouth  and 
the  articulation  taken.  This  can  be  in  plaster,  modelling  composition 
or  wax,  as  it  will  be  attached  to  the  caps  and  the  saddle  and  will  come 
away  with  them  so  that  there  will  be  no  danger  of  distorting  the  articu- 
lation by  pressing  it  back  in  position  on  the  ca.st.  The  cast  is  then  pre- 
pared and  the  bridge  constructed. 

In  constructing  a  saddle  bridge  it  is  better  that  the  facings  should  not 
be  ground  to  fit  the  saddle  exactly,  but  should  stand  away  from  it  for  a 
little  distance,  (Fig.  810),  the  object  of  which  will  be  seen  later.  The 
tips  of  the  facings  should  be  high  enough  to  touch  the  lingual  side  of 
the  buccal  cusps  of  the  upper  molars  as  in  Fig.  810,  A. 

After  the  facings  have  been  ground  they  are  held  in  place  with  wax 


THE  ADJUSTMENT  OF  THE  SADDLE   TO   THE  RTDGE.        7(>1 


ami  a  wall  of  plaster  l)uilt  iij)  on  the  buccal  side  so  as  to  retain  them  in 
position  after  the  wax  has  been  removed.  (I'ig-  'SW.)  The  facings 
are  then  removed  and  the  occlusal  ends  ground  oft'  at  an  angle  of  about 
forty-five  degrees  with  the  backs  or  Ungual  side  as  in  Fig.  811,  A,  leav- 
ing them  so  that  they  will  clear  the  occluding  teeth  by  about  a  thirty- 
second  of  an  inch.  The  facings  are  then  backed  with  thin  platinum, 
the  backings  touching  each  other  and  extending  from  the  beginning  of 
the  bevel  at  the  occlusal  end  to  the  saddle,  which  they  shoidd  touch 
closely  all  along,  (Fig.  812.)  The  facings  are  then  waxed  firmly  to 
the  saddle  with  hard  adhesive  wax,  the  wax  being  high  enough  to 
support  and  hold  the  cusps.  (Fig.  813.)  A  solid  cusp  must  be  used, 
the  buccal  side  ground  or  filed  to  fit  the  bevel  of  the  facnig  and  waxed 
in  place. 

The  buccal  and  lingual  sides  are  next  covered  with  wax,  the  pink 
paraffin  and  wax  being  preferable  as  it  is  not  sticky  and  carves  nicely. 
Both  sides  are  then  carved  to  represent  the  natural  gums.  This  sliould 
be  done  very  carefully  and  the  wax  made  perfectly  smooth  in  order  to 
secure  a  clean  die,  so  that  when  the  plates  are  struck  up,  they  will  re- 
quire no  finishing  other  than  with  pumice  and  rouge. 

On  the  buccal  side  it  should  be  carried  above  the  lower  edge  of  the 
facings  and  well  up  between  them,  as  in  Fig. 
814.      The    car^dng    on    the    lingual   side 
should  correspond  in  depth   and    breadth 
to  the  facings   on  the  buccal  side. 

An  impression  is  then  taken  of  each 
side  separately,  carrying  the  plaster  well 
above  the  gum  line  and  over  the  heel  on  the 
buccal  side,  and  on  the  lingual  side,  well  above  the  cusps  and  below 
the  saddle  and  far  enough  over  the  heel  to  meet  the  impression  from 
the  buccal  side.  (Fig.  815.)  The  impression  should  be  deep  enough 
to  serve  as  a  model  from  wdiich  to  get  good  strong  dies. 


Fig.  814 


Fig  815 


Fig.  816 


Fig  817 


The  dies  and  counter-dies  made,  the  buccal  plate  is  struck  up  from 
No.  30  gauge  coin  gold  and  festooned  carefully  to  fit  around  the  facings. 
The  lingual  plate  is  struck  from  No.  28  gauge  coin  gold  and  fitted  care- 
fully, the  part  going  over  the  heel  being  brought  in  contact  with  that 
from  the  buccal  side.  After  they  have  been  cleansed  in  acid  the  buccal 
plate  is  placed  in  position  and  held  wdth  small  iron  wire  clamps,  as  in 
Fig.  816.  The  saddle  is  then  held  over  a  small  alcohol  flame  for  a  moment 


ro2 


AN  ASSEMBLAGE  OF  UNITED  CROWNS. 


to  loosen  llio  wax  from  {lie  plate  and  tli(>  teeth  and  wax  rejiioved  and 
laid  carefnlly  aside.  The  saddle  is  then  invested,  lingnal  side  down, 
only  just  enough  of  the  investment  being  used  to  keep  it  from  springing. 
(Fig.  817.)  The  investment  is  thoroughly  dried  out,  the  piece  well 
fluxed  and  some  j)ieees  of  IS-carat  solder  dropped  in  between  the 
saddle  and  the  plate.  It  is  then  well  heated  up  and  when  it  has 
rached  a  red  heat,  the  blowpipe-flame  is  thrown  on  the  imder  side  of 
the  saddle  next  to  the  investment  and  the  solder  drawn  through  all 
around.  After  it  has  been  allowed  to  cool,  it  is  cleansed  in  acid,  and 
the  saddle  warmed  slightly  and  the  teeth  pressed  back  into  place  until 
the  fitting  of  the  lingual  plate  show  that  they  are  in  their  correct  posi- 
tion.     The  bridge  is  now  ready  for  the  final  soldering. 

The  piece  is  invested,  buccal  side  down,  the  investment  on  the  oc- 
clusal side  covering  about  two-thirds  of  the  cusps  and  the  saddle,  to 
within  about  one-eighth  of  an  inch  of  the  lingual  edge.  (Fig.  818, 
A  and  B.) 

After  the  investment  has  hardened  it  is  warmed  a  little  and  the  wax 
lifted  out.  It  is  then  thoroughly  heated  up  to  a  light  red  heat,  fluxed 
and  soldered  between  the  cusps  with  20-carat  solder,  the  backings 
beino-  united  and  connected  with  the  saddle  with   the   same  solder, 


Jig.  818 


Fig.  820 


enough  being  used  to  give  sufficient  strength  and  support  to  the  bridge. 
(Fig.  819.)  Some  18-carat  solder  is  then  melted  over  the  lingual 
side  of  the  saddle  and  cusps  at  A  and  B,Fig.  819  andthehngual  plate 
carefully  put  in  place,  having  been  previously  fluxed  on  the  inner  side. 
The  wdiole  investment  is  then  thoroughly  heated  to  a  bright  red  heat 
and  the  flame  of  the  blowpipe  passed  along  the  under  side  of  the  saddle 
and  the  exposed  portion  of  the  cusps  (Fig.  820),  until  the  solder 
has  been  drawn  through  and  united  the  lingual  j)late  all  around. 

The  greatest  care  nuist  be  exercised  in  putting  on  this  plate,  as  it 
has  to  l)e  heated  so  very  hot  that  it  is  easily  burned. 

After  it  has  cooled  it  is  removed  from  the  investment,  boiled  in  dilute 
sulphuric  acid,  washed  and  then  dipped  in  alcohol  and  thoroughly 
dried.  The  points  of  the  buccal  plate  which  have  been  carried  up  be- 
tween the  facings  are  now  bent  outward  and  the  space  between  the 
plate  and  the  saddle  and  under  the  facings  is  filled  with  oxyphosphate 
of  zinc.  While  the  cement  is  yet  soft,  the  points  of  the  plate  are  pressed 
back  again  between  the  facings.  After  it  has  hardened,  the  cement 
is  cleaned  out  from  between  tlie  teeth  and  plastic  gold  packed  in  and 
over  the  points  of  the  plate.  The  bridge  is  then  ready  to  articulate  and 
finish. 


CEMENTING  OF  REMOVABLE  BRIDGE.  7G3 


CEMENTING  OF  REMOVABLE  BRIDGES. 

In  cementing  a  removable  bridge,  the  inner  caps  are  placed  in  posi- 
tion in  the  onter  caps  and  wax  flowed  over  the  joints  to  prevent  any  of 
the  cement  from  working  in  between  them.  The  bridge  is  then  ce- 
mented in  the  mouth  in  the  same  way  as  though  it  were  a  fixed  piece.  It 
is  better  to  leave  it  in  the  mouth  for  several  hours  before  attempting  to 
remove  it,  so  as  to  give  time  for  the  cement  to  get  perfectly  set  and  hard. 
It  can  then  be  taken  out  and  the  excess  of  cement  removed  from  under 
the  gums  and  around  the  teeth.  A  little  campho-phenique  wiped 
around  the  teeth  and  on  the  gums  will  relieve  the  soreness  caused  by 
the  instrument. 

COMBINATIONS  OF  THE  PRINCIPLES  OF  PLATE-  WITH  THOSE  OF 

BRIDGE-WORK. 

The  principle  involved  in  this  class  of  mechanism  was  utilized  early 
in  the  present  century  as  a  means  of  retention  for  partial  dentures. 
There  is  a  combination  of  the  support  represented  in  the  bearing  of  a 
plate  upon  the  alveolar  ridge,  together  with  the  rigidity  secured  by 
having  terminals  or  extensions  from  the  plate  anchored  in  the  roots  of 
teeth  or  embracing  them  as  closed  and  rigid  cylinders. 

The  principle  of  anchorage  in  the  roots  of  a  natural  tooth  is  that  of 
embracing  the  natural  teeth  by  closed  cylinders;  a  combination  of  the 
two  means  of  retention. 

These  devices  posses  certain  advantages  over  clasp  plates,  in  that 
there  is  no  elasticity  of  ihe  retaining  cylinders ;  they  slip  over  the  abut- 
ments prepared  for  their  reception,  and  being  closely  adapted  to  them, 
there  is  a  greater  rigidity  of  the  dentures  than  with  the  ordinary  clasp. 

For  their  employment  it  is  obviously  necessary  that  the  abutments 
should  have  sides  which  are  parallel  and  the  axes  of  both  mutually 
parallel.  They  are  usually  designed  for  application  in  cases  where  the 
natural  teeth  are  in  such  positions  and  have  forms  which  would  fit  them 
to  serve  as  bridge  abutments,  but  the  contour  of  the  gum  is  such  that  it 
is  necessary  to  employ  gum  teeth  (Fig.  821.)  They  are,  to  all  intents 
and  purposes,  removable  bridges,  having  a  greatly  multiplied  support 
from  the  natural  gum. 

It  was  stated  in  describing  the  bulkhead  bridge,  that  should  the 
contour  of  the  gum  be  lost  to  such  an  extent  as  to  preclude  the  appli- 
cation of  a  bridge,  owing  to  the  impossibility  of  correctly  adapting 
plain  teeth,  a  removable  plate  bridge  might  be  employed.  A  removable 
bridge  may  be  adapted  to  such  a  case  as  follows : 

The  canines  roots  are  properly  trimmed  and  capped.  Removable 
crowns  are  fitted  to  them.  A  gold  plate  is  swaged  to  fit  the  gum  be- 
tween the  teeth,  extending  high  enough  on  its  labial  aspect  to  furnish 
adequate  support  to  the  artificial  gums,  and  the  palatal  edges  far  enough 
to  furnish  adequate  support  to  the  stays  of  the  teeth.     The  plate  is  to  be 


r64 


A  A'  ASSEMBLAGE  OF  UXITED  CROWWS. 


made  of  two  layers — tliat  next  the  natural  gum  of  No.  32  pure  gold,  and 
covered  by  a  plate  of  No.  32  platinous  gold:  the  two  are  accurately 
adapted  to  one  another  and  united  by  means  of  20-carat  solder.  The 
ends  are  to  be  accurately  adapted  to  the  abutment  crowns.  Plate  and 
crowns  are  set  in  position  in  the  mouth,  and  a  wax-bite  taken:  this  is 
removed  and  set  aside.  While  the  pieces  are  in  position  an  impression 
of  modelling  composition  is  taken.     Modelling  composition  is  preferred 


FiH.  821 


Fig.  822 


to  plaster,  because  the  pressure  upon  the  plate  forces  the  latter  into  ac- 
curate contact  with  the  soft  tissues.  Should  plaster  be  employed,  a 
ridge  of  softened  wax,  wide  enough  to  fit  betw^een  the  abutments,  is 
set  in  the  impression  tray,  and  over  it  the  plaster.  Now,  when  the  im- 
pression is  taken  the  plate  is  pressed  up  by  the  wax  sufficiently  to  ensure 
that  the  natural  gum  shall  furnish  support  to  the  finished  bridge.     A 


Fig.  S23 


View  of  left  side  of  the  mouth,  showing    bicuspids  and  molars  in  contact  with  the  ridge  of 

the  lower  jaw. 

cast  is  made  and  an  articulation  mounted.  Should  the  plate  be  exposed 
by  the  movements  of  the  lips,  it  may  be  necessary  to  adapt  gum  teeth 
(Fig.  821);  if  not,  plain  teeth  are  fitted;  the  gum  is  to  be  subsequently 
formed  of  pink  vulcanite.  The  teeth  are  to  have  stays  fitted.  The 
abutment  crowns  are  removed  from  the  cast,  and  they,  the  teeth  and 
the  plate,  boiled  in  acid.     They  are  returned  to  the  cast  and  joined  to- 


REMOVABLE  PLATE-BRIDGE.  765 

gether  by  means  of  adhesive  wax:  a  wire  laid  across  the  backs  from  one 
abutment  crown  to  the  other,  and  covered  by  adhesive  wax,  holds  them 
in  position.  They  are  invested,  and  when  the  investment  is  set,  pieces 
of  triangular  wire  are  placed  at  the  junction  of  the  plate  with  the  abut- 
ment crowns,  and  the  pieces  are  attached  to  one  another  by  means  of 
20-carat  solder.  If  plain  teeth  have  been  employed,  and  contouring  is 
inchcated,  a  vulcanite  gum  is  attached  to  the  plate. 

Figs.  823  and  824  show  a  remarkably  distorted  occlusion  produced 
/primarily  by  the  loss  of  the  left  lower  bicuspids  and  molars,  and  the 
right  upper  second  bicuspid  and  molars,  and  the  wearing  away  of 
the  anterior  teeth.  It  will  be  observed  that  the  left  upper  bicuspids 
and  molars  and  the  right  lower  bicuspids  and  molars  are  in  contact 
with  the  gums  on  the  tops  of  the  respective  ridges,  this  condition  being 

Fig.  824 


View  of  right  side  of  the  mouth,  showing  lower  molars  and  bicuspids  in  contact  with  the 
ridge  of  the  upper  jaw. 

caused  by  the  shortening  of  the  bite  incident  to  the  attrition  of  the  an- 
terior upper  and  lower  teeth.  The  treatment  of  this  case  consisted  in 
the  construction  of  upper  and  lower  partial  dentures  which  embraced 
the  principles  involved  in  the  combination  of  the  ordinary  removable 
plate  with  those  of  removable  bridge-work.  The  procedure  was  as 
follows :  the  upper  and  lower  anterior  teeth,  several  of  which  were  worn 
nearly  to  the  gum-margin,  were  de\'italized,  cut  down  to  uniform  length 
and  form,  and  provided  with  caps  and  hollow  posts,  over  which  tele- 
scoping caps  with  solid  posts  were  accurately  fitted,  similar  to  that  of  tile 
Richmond  removable  crown.  The  plates  which  were  to  unite  the  caps 
having  the  solid  posts  and  to  cover  the  alveolar  ridge  where  bicuspids 
and  molars  had  been  lost,  were  constructed  in  two  laminae,  the  first  of 
22-carat  gold  of  No.  29  gauge  and  the  second  of  platinous  gold  of  No. 
26.  The  finer  gold  admits  of  more  accurate  adaptation  to  the  plaster  cast 
while  the  platinous  gold  affords  the  desired  strength;   the  two  were 


7(iO 


AN  ASSEMBLAGE  OF  US  IT  El)  CliOWXS. 


united  with  solder,  as  is  usiud  in  the  construction  of  h)\ver  plates.  The 
caps  with  the  hollow  posts  were  cemented  to  place,  the  telescoping  caps 
with  the  solid  posts  and  the  plate  were  placed  in  position,  care  having 
been  taken  to  maintain  the  correct  relation  of  one  to  the  other,  and  an 
impression  was  taken  in  plaster  as  previously  described.     In  removing 


Fig.  825 


the  impression  it  is  desirable  that  the  plate  and  caps  should  come  away 
with  it.  A  model  is  then  cast  of  sand  and  plaster  which  held  the  plate 
and  caps  in  proper  relation  uniil  they  were  united  by  solder,  after  which 
the  succeeding  details  of  construction  were  the  same  as  in  ordinary 
plate-work. 

Fig. 820 


The  completed  dentures  are  shown  in  the  illustrations  (Figs.  825  and 
826.)  The  bite  was  opened  sufficiently  to  restore  normal  relations. 
All  of  the  remaining  natural  teeth  were  perfectly  firm  and  gave  promise 
of  a  long  period  of  usefulness. 


THE    USE    OF    PORCELAIN    CROWNS    IN    BRIDGE-WORK. 


With  the  advent  of  the  casting  process  came  the  more  general  use  of  all 
porcelain  crowns  for  bridge-work  in  place  of  the  veneers  which  had  here- 
tofore been  used  to  partially  hide  the  mass  of  gold  which  the  bridge 
proper  was  constructed,  thus  producing  much  more  artistic  effects  than 
was  possible  by  the  old  method. 

Any  of  the  crowns  of  the  different  manufacturers  which  come  nearest 
in  mold,  shade,  and  texture  to  the  requirements  of  the  case  can  be 
used.  There  must  be  sufficient  depth  of  the  bite  to  allow  of  every  crown 
having  a  base  deep  enough  to  give  strength  and  stability  to  the  bridge. 


THE   USE  OF  PORCELAIN  CROWNS  IN  BRIDGE- WORK.       767 

These  bases  are  preferably  cast,  although  it  is  possible  for  one  possessing 
the  necessary  skill  to  make  them  by  swaging  and  soldering. 

The  greatest  difficulty  with  which  we  have  to  contend  in  making  these 
bases  is  due  to  the  contraction  of  the  cast  metal  on  cooling.  The  result 
is  that  the  crowns  do  not  fit  as  they  should  and  there  is  more  or  less 
cutting,  trimming,  and  fitting  to  do,  before  they  will  go  in  place,  and  not 
infrequently  it  is  necessary  to  do  the  work  over  again  and  perhaps  not 
even  then  will  the  desired  result  be  attained. 

The  method  has  been  tried  of  first  burnishing  or  swaging  pure  gold 
over  the  bases  of  the  crowns  and  then  waxing  up  and  casting  over  the 
pure  gold.  This  has  perhaps  improved  matters  somewhat,  but  still  it  is 
very  rarely  that  it  has  been  possible  to  secure  anything  like  a  perfectly 
fitting  base,  especially  if  the  crowns  are  of  any  considerable  size,  for  with 
the  larger  castings  there  is  a  proportionately  greater  amount  of  shrink- 

In  1911,  Frank  W.  Peeso  conceived  the  idea  of  building  out,  or  enlarg- 
ing, the  base  of  the  crown  before  waxing,  in  order  to  make  up  for  the 
shrinkage  of  the  gold,  and  he  hit  upon  a  plan,  the  carrying  out  of  which, 
while  not  entirely  overcoming  the  difficulty  in  every  instance,  which  is 
probably  due  to  faulty  technique,  has,  in  the  majority  of  cases,  reduced 
the  trouble  to  a  minimum. 

This  method  does  not  do  away  with  the  shrinkage  of  the  gold,  for  that 
is  an  inherent  property,  which  nothing  can  overcome,  but  by  it  we  coun- 
teract or  make  allowance  for  this  contraction  of  the  metal  on  cooling. 

The  method  of  procedure  is  first  to  swage  or  burnish  tin  foil,  of  vary- 
ing thicknesses  according  to  the  size  of  the  crown,  over  the 
base,  in  reality  making  a  base  of  the  metal,  as  in  Fig.  827.     It        ^^*^-  ^^^ 
is  then  lubricated  and  the  wax  base  is  built  over  the  tin  foil, 
the  lubricated  surface  allowing  its  easy  removal.     The  size 
of  the  base  of  the  crown  has,  of  course,  been  increased  the 
amount  of  the  thickness  of  the  tin.     We  have  thus  made 
allowance  for  the  shrinkage,  so  that  when  the  crown  is  placed  in  the 
casting  it  fits  very  closely,  and  if  we  have  been  very  careful  in  our  tech- 
nique, there  will  be  little  or  no  trimming  to  be  done. 

The  thickness  of  the  tin  foil  varies  according  to  the  size  of  the  crown, 
the  largest,  of  course,  requiring  the  heaviest  foil.  Three  sizes  are  used, 
the  first  being  about  .005,  the  second  .007,  and  the  third  .009  of  an  inch  in 
thickness. 

The  burnishing  of  the  foil  over  the  bases  is  very  quickly  and  easily 
done.  The  lighter  foil  can  be  pressed  nearly  to  place  with  a  piece  of 
soft  rubber  and  the  wrinkles  at  the  edges  smoothed  out  with  the  thumb- 
nail or  a  piece  of  orange  wood.  With  the  heavier  foils  a  piece  of  orange- 
wood  and  a  small  burnisher  are  all  that  is  required  to  secure  the  close 
adaptation  which  is  necessary  to  insure  a  perfectly  fitting  base. 

In  making  the  bases  for  a  series  of  crowns  for  a  bridge,  it  is  not  advis- 
able to  cast  them  together  in  one  piece,  as  if  the  bridge  is  of  any  con- 
siderable length,  the  shrinkage  would  be  proportionately  great  in  that 
direction,  so  that  it  would  be  necessary  to  grind  the  crowns  on  their 


768 


AN  ASSEMBLAGE  OF   UNITED  CROWNS. 


approximal  surfaces,  before  they  would  go  into  position  on  their  bases. 
This  would  result  in  shortening  of  the  bridge  and  leaving  a  space  between 
it  and  the  adjoining  teeth  or  abutments.  The  best  way  is  to  cast  these 
bases  separately,  and  in  no  instance  should  more  than  two  be  cast  to- 
gether. The  casting  of  each  base  separately  and  afterward  uniting  them 
does  away  with  the  shrinkage  which  would  otherwise  take  place. 

The  casting  of  the  bases  for  abutment  crowns  may  be  done  directly 
on  the  caps,  or  they  may  be  cast  separately  and  afterward  soldered  to 
the  caps.  The  latter  \Aay  is  preferable  in  remo\able  work  as  there  is 
less  danger  of  disturbing  the  accuracy  of  adjustment  between  the  outer 
and  the  inner  caps. 

The  same  method  of  procedure  obtains  where  a  saddle  is  used  as  an 
additional  support  to  the  abutments  and  the  crowns  mounted  on  this 
saddle.  If  there  is  no  great  depth  between  the  occluding  teeth  and  the 
saddles,  the  crowns  are  ground  so  as  to  leave  sufficient  space  for  the  base. 
(Fig.  828.)  The  crowns  are  tinned  in  the  manner  described  and  the  wax 
flowed  between  the  bases  and  the  saddle  which  has  pre\iously  been  lubri- 
cated. They  are  then  carved  and  removed  from  the  crowns  and  saddles 
separately,  the  sprue  wire  attached  to  the  lingual  side  and  the  bases  cast. 

They  are  afterward  adjusted  in  position  on  the  saddle  and  invested, 
each  piece  being  held  in  place  by  a  little  wire  clamp,  the  wire  passing 


Fig.  829 


Fig.  830 


Fig.  828 


Fig.  8.31 


from  the  top  of  the  post  to  the  under  part  of  the  saddle  directly  beneath. 
(Fig.  829.)  With  the  half  cap,  the  clamp  extends  from  the  top  of  the 
post  to  the  under  side  of  the  floor.     (Fig.  830.) 

The  in\'estment  should  be  very  light  and  just  fill  the  under  side  of  the 
cap  or  saddle,  leaving  the  whole  of  the  upper  parts  exposed.  This  facili- 
tates the  thorough  heating  up  of  the  piece  and  the  solder  is  easily  drawn 
through  from  the  lingual  side,  uniting  the  bases  to  the  saddle  and  to  each 
other.  The  crown  side  of  the  bases  should  be  well  coated  with  whiting 
or  some  antiflux,  so  that  there  will  be  no  danger  of  the  solder  flo\N'ing 
over  this  surface  and  destroying  the  fit  of  the  crowns. 

Saddles. — ^The  saddles  are  struck  up  of  32  gauge  soft  platinum  plate 
and  are  afterward  heavily  reinforced  by  flowing  coin  gold  over  the 
outer  surface,  after  which  they  are  adjusted  in  the  mouth  and  their  rela- 
tion to  the  abutments  obtained  by  taking  an  impression  over  the  abut- 
ments and  saddle,  while  the  saddle  is  pressed  firmly  into  the  tissues. 

Deep  Saddle. — AYhere  there  has  been  a  considerable  amount  of  re- 
sorption and  there  is  a  great  depth  between  the  occluding  teeth  and  the 


THE   USE  OF  PORCELAIN  CROWNS  IN  BRIDOE-WORK.       7G9 

ridge,  it  would  make  these  pieces  unnecessarily  and  undesirably  heavy  to 
build  solid  bases  extending  from  the  crowns  to  the  saddle.  This  will 
apply  where  there  is  to  be  an  abutment  at  each  end  of  the  bridge  and 
also  in  extension  saddles  which  are  anchored  only  at  one  end,  as  in  the 
lower  jaw  where  the  molars  are  missing.  The  lower  edges  of  the  crowns 
are  beveled  so  that  the  bases  may  come  up  over  the  gingival  edge, 
gripping  them  tightly,  thus  affording  a  firm  seat  and  minimizing  the  ^^ 
possibility  of  fracture.  HP 

.  The  bases  may  be  made  in  the  form  of  a  ring,  covering  the  beveled  edge 
and  extending  just  far  enough  underneath  to  form  a  positive  seat  for  the 
crown,  as  in  Fig.  831.  These  bases  are  cast  in  the  usual  manner  and 
after  being  united  to  each  other  are  soldered  to  the  abutment  caps  mesi- 
ally  and  distally,  or  in  the  case  of  an  extension  saddle  mesially  to  the 
crown  serving  as  an  abutment  and  distally  to  the  saddle,  leaving  the 
connecting  rings  suspended  between  these  points,  as  in  Fig.  832.  The 
crowns  are  then  placed  in  position  in  the  bases  and  the  buccal  and  lingual 
sides  between  the  bases  and  saddle  filled  in  with  wax,  and  carved  so  as  to 
restore  the  gum  contour,  leaving  nearly  one-eighth  of  an  inch  of  the  edge 
of  the  saddle  exposed,  and  coming  about  midway  on  the  labial  and 
lingual  side  of  the  ring  bases.  (Fig.  833.)  Impressions  are  then  taken 
of  these  carved  surfaces  and  models  prepared.     Dies  and  counter-dies 

Fig.  832  Fig.  833  Fig.  834 


are  made  and  plates  of  28  or  30  gauge  coin  gold  struck  up  and  carefully 
fitted  and  adjusted  to  the  saddle.  The  wax  is  then  removed  and  the 
crowns  taken  from  their  bases.  One  of  the  plates  is  put  in  position  and 
held  in  place  with  a  clamp  over  the  edge  of  the  saddle  and  the  piece 
placed  in  the  investment,  open  side  down,  leaving  the  side  on  which  the 
plate  is  to  be  soldered  exposed,  as  in  Fig.  834.  The  investment  is  dried 
out  and  the  inside  of  the  ring  bases  coated  heavily  with  whiting  or 
other  anti-flux.  The  piece  is  then  well  fluxed  between  the  plate  and  the 
saddle  and  also  between  it  and  the  rings,  which  are  thoroughly  united 
wdth  solder,  preferably  20  carat. 

After  it  has  been  removed  from  the  investment,  it  is  cleansed.  The 
plate  for  the  opposite  side  is  then  clamped  in  position  and  the  piece 
invested  and  soldered  in  the  same  manner  as  the  first.     (Fig.  834.) 

The  object  in  making  a  saddle  in  this  way  instead  of  casting  what  might 
be  called  the  entire  shell,  and  then  uniting  it  to  the  saddle,  is  that  in  the 
rolled  coin  gold  plates  we  have  a  perfectly  dense  homogeneous  mass  that 
can  be  easily  polished  and  which  takes  and  retains  a  very  high  finish, 
while  the  surface  of  a  casting  is  more  or  less  porous  and  will  not  take  a 

49 


770  AN  ASSEMBLAGE  OF   UNITED  CROWNS. 

high  polish.     It  also  is  much  lighter  and  stronger  than  it  could  possibly 

be  made  by  casting. 

The  saddle  is  cleansed  in  acid  and  polished  and  is  ready 
for  the  crowns.  The  crowns  are  fitted  with  posts  which 
extend  through  the  opening  in  the  bases  into  the  body  of  the 
saddle.  These  posts  are  cemented  into  the  crowns,  the  hol- 
low body  of  the  saddle  filled  with  cement,  and  the  crowns 
put  in  place  and  held  there  under  pressure  until  the  cement 
is  hardened.  (Fig.  835.)  A  saddle  made  in  this  way  pre- 
sents a  most  beautiful  appearance  and  does  away  entirely 

with  the  showing  of  the  gold.     At  the  same  time  we  have  obtained  a 

maximum  amount  of  strength  with  a  minimum  amount  of  weight. 

PORCELAIN    CROWN-  AND   BRIDGE-WORK. 

In  the  discussion  of  porcelain  work  many  matters  present  them.selves 
for  our  consideration.  Regarded  from  a  purely  aesthetic  point  of  view, 
porcelain  is  the  ideal  material  of  which  crowns  and  bridges  should  be 
constructed,  but  from  the  practical  side  other  things  than  appearance 
must  also  be  considered. 

If  the  restoration  of  the  missing  teeth  were  only  made  for  the  purpose 
of  improving  the  personal  appearance  of  the  patient,  then  porcelain 
should  be  used  in  every  case,  but  this  should  be  a  secondary  consider- 
ation. 

The  health  of  the  patient,  depending  as  it  does  to  a  very  great  extent 
on  the  ability  of  the  masticatory  organs  to  properly  perform  their  func- 
tions, demands  that  the  question  of  utility  should  be  given  the  first  im- 
portance. 

Porcelain  is  of  necessity,  a  very  fragile  material  and  where  great 
strength  is  required,  it  is  wholly  unsuitable  for  use. 

A  tremendous  force  is  exerted  by  the  jaws  and  widely  varying  figures 
are  given  as  to  the  exact  amount.  Dr.  G.  V.  Black^  has  estimated  the 
force  exerted  in  mastication  as  follows.  "For  the  incisors,  the  maximum 
force  exerted,  one  hundred  and  seventy  five  (175)  pounds,  minimum 
force,  thirty  (30)  pounds.  For  the  molars,  maximum  force,  two  hun- 
dred and  forty  (240)  pounds:  minimum  force,  seventy  (70)  pounds. 
Force  exerted  in  masticating  tough  meats  ninety  (90)  pounds:  tender 
meats,  thirty  (30)  pounds.  Hard  crusts  resist  a  pressure  of  two  hun- 
dred and  fifty  (250)  pounds;  hard  candy,  one  hundred  (100)  pounds." 

There  is  no  porcelain  body  made  which  can  successfully  withstand 
the  continuous  strain  to  which  a  bridge  will  be  subjected. 

Undoubtedly,  porcelain  has  its  place  in  crown-and  bridge-work,  but 
until  some  method  is  discovered  whereby  it  can  be  annealed  so  as  to 
render  it  tough  and  to  a  certain  extent  pliable,  its  uses  will  be  limited  to 
single  crowns  and  bridges  on  wdiich  there  will  be  very  little  strain. 

For  single  crowns  where  there  is  sufficient  depth  to  allow  of  a  con- 

'  The  Dental  Cosmos,  vol.  xxxvii.,  p.  474. 


PORCELAIN  CEOWN-  AND  BRIDQE-WORK.  771 

siderablc  amount  of  body  being  used,  porcelain  can  be  employed  with 
good  results.  Where  teeth  have  been  lost  and  much  absorption  has 
taken  place,  so  that  there  is  a  great  depth  between  the  gum  and  the 
occluding  teeth  of  the  opposite  jaw,  porcelain  will  make  a  much  more 
artistic  piece  of  work,  but  it  can  never  be  as  serviceable  as  a  well  made 
and  perfectly  articulated  gold  bodied  bridge.  If  porcelain  is  used,  the 
work  should  always  be  made  removable,  or  it  should  be  set  in  such  a 
manner  that  it  can  be  easily  removed  for  repair  in  case  of  accident,  for 
jsuch  a  bridge  cannot  be  repaired  in  the  mouth. 

Where  an  upper  or  lower  plate  is  worn,  a  porcelain  bridge  has  a 
much  better  chance  of  a  long  period  of  usefulness  for  a  time,  than 
where  it  occludes  with  the  natural  teeth,  for  the  force  exerted  in  masti- 
cation is  very  much  less  where  a  plate  is  used. 

In  all  cases  where  porcelain  is  used,  the  bulk  of  body  must  be  as  great 
as  it  is  possible  to  make  it.  It  should  never  be  placed  in  thin  layers 
over  bands  or  any  of  the  attachments  or  metal  work  of  the  crown  or 
bridge.  Sooner  or  later  the  porcelain  is  sure  to  flake  off,  exposing  the 
platinum,  rendering  the  piece  unsightly  and  leaving  sharp  ragged 
edges  of  porcelain  to  cut  and  irritate  the  soft  tissues. 

If  the  root  of  a  tooth  which  is  to  be  crow^ned  sets  inside  of  the  arch,  so 
as  to  necessitate  the  setting  of  the  facing  beyond  the  labial  side  of  the 
cap,  it  should  he  carried  far  enough  over  to  allow  of  placing  a  thick  rope 
of  porcelain  over  the  band,  which  should  be  well  stippled  in  order  to 
give  a  mechanical  hold  for  the  body. 

WORKING  OF   PORCELAIN    BODY. 

In  the  putting  on  of  the  porcelain  body,  it  should  not  be  w^orked  too 
soft,  but  should  be  of  the  consistency  of  very  thick  dough 
or  putty.     The  pin  of  the  bridge  or  crown  is  grasped  in  '^^°-  ^^'^ 

the  jaws  of  a  pair  of  suitable  pliers  or  of  a  pin  vise  and  a 
portion  of  the  body  placed  on  the  cap  as  in  Fig.  836,  and 
carried  under  the  facing  and  over  the  cap  by  tapping  the 
vise  or  by  raking  back  and  forth  across  it  with  a  rough 
handled  instrument.  This  will  cause  the  body  to  spread, 
bringing  the  moisture  to  the  surface,  wdiich  should  be  taken 
up  with  bibulous  paper  or  a  clean  napkin.  More  body  is 
added  as  needed,  taking  up  the  moisture  as  before,  until 
the  crown  is  built  up  sufficiently,  after  which  it  is  carved 
to  represent  the  tooth  which  it  is  designed  to  replace.  It  is  now  ready 
for  baking. 

THE  BAKING   OF  PORCELAIN. 

The  best  results  in  the  fusing  of  porcelain,  as  in  many  other  things 
connected  with  this  work,  are  only  secured  after  long  experience.  The 
first  baking  is  called  a  biscuiting.  In  a  perfect  biscuit,  the  body  must  be 
thoroughly  fused,  presenting  a   somewhat   granular    appearance,  but 


772  AN  ASSEMBLAGE  OF  UNITED  CROWNS. 

is  not  perfectly  glazed.  The  porcelain  is  strongest  at  this  point. 
For  the  biscuit  body,  it  is  well  to  use  a  high  fusing  body  and  for  the 
final  baking,  a  medium  fusing  body,  or  enamel. 

When  the  body  is  fused,  there  is  a  certain  amount  of  shrinkage, 
about  one-seventh  of  its  bulk,  and  also  some  checking  of  the  body. 
The  crown  is  replaced  in  a  pin  vise  and  built  up  a  second  time,  with 
the  medium  body,  or  enamel,  in  the  same  manner  as  before  and 
given  a  second  baking,  this  time  glazing  perfectly.  It  may  be  some- 
times necessary  to  give  it  more  than  the  two  bakings. 

PORCELAIN    BRIDGE-WORK, 

The  general  plan  and  methods  followed  in  this  class  c^f  bridge-work 
are  those  of  Dr.  E.  Parmley  Brown,  who  originated  it. 

The  objections  urged  against  bridge-work  composed  of  fine  gold  and 
porcelain  facings  united  by  means  of  fine  solders — that  the  spaces  be- 
tween the  gum  and  the  palatal  surfaces  of  bridge  were  unclean;  that 
the  oxidation  of  the  base  metals  of  the  solder  permitted  the  accumulation 
of  offensive  materials;  and  that  the  porcelain  facings  were,  through 
lack  of  bulk,  in  constant  danger  of  fracture — led  to  the  devising  of  this 
method,  designed  to  overcome  the  several  objections  specified. 

The  bridge  as  made  and  recommended  by  Dr.  Brown  consists  of  a 
rigid  supporting  and  anchoring  bar,  to  which  are  adapted  porcelain 
teeth,  subsequently  united  to  the  bar  and  to  one  another  by  means  of 
porcelain  fused  about  the  parts. 

The  usual  method  of  anchoring  the  bridge  is  by  means  of  arms  ex- 
tending from  the  ends  of  the  bridge,  which  are  anchored  in  cavities 
formed  in  the  natural  teeth  for  their  reception.  Instead  of  what  are 
called  "self-cleansing  spaces,"  the  base  of  the  bridge  presses  firmly  upon 
the  natural  gum,  wath  a  view  to  excluding  even  the  secretions  of  the 
mouth.  A  base-plate  of  iridio-platinum  may  be  accurately  fitted  to  the 
gum,  to  which  the  porcelain  of  the  bridge  is  to  be  attached. 

A  typical  case  for  the  application  of  this  variety  of  bridge  is  that  of 
the  bulkhead — two  canine  roots  supporting  six  artificial  crowns.     The 

Fig.  837 


abutment  roots  are  prepared,  a  platinum  cap  fitted  to  each;  the  edges  of 
the  caps  are  left  projecting  beyond  the  edges  of  the  roots,  then  slit  (Fig. 
837,  A),  bent  over,  and  adapted  to  the  Avails  of  the  roots  in  the  mouth 
(Fig.  837,  B).  The  root-canals  are  enlarged  and  deepened,  and  metal 
posts  filed  to  fit  them  are  placed  through  openings  made  through  the 


PORCELAIN  BEIDGE-WORK. 


773 


caps  into  the  root-canals.  A  bite  is  taken;  then  an  impression  is 
obtained,  in  whicli  the  caps  and  wires  are  withdrawn.  An  articulating 
model  is  made,  and  facings  selected  and  ground  into  position.     The 


Fig, 838 


Fin.  8.39 


Porcelain  metal  band. 


race  of  the  cast  is  varnished  and  oiled,  and  a  plaster  wall  formed  about 
the  teeth  and  cast,  holding  the  former  rigidly  in  position.  A  piece  of 
annealed  brass  wire,  three  inches  long,  has  one  extremity  filed  to  occupy 
the  pulp-canal  of  a  canine  root  to  the  depth  it  is  designed  to  carry  the 
anchoring  bar;  the  wire  above  the  cap  is  flattened  to  a  distance  which 
shall  permit  perforating  it  for  the  reception  of  the  pins  for  the  canine 
teeth.  The  wire  is  bent  at  right  angles,  then  carried  across  the  poster- 
ior surfaces  of  the  incisor  crowns;  it  is  to  occupy  the  space  between  the 
pins  of  these  teeth.  Above  the  upper  pin  of  the  opposite  canine  crown 
it  is  again  bent  at  right  angles;  the  lower  end  is  shortened  to  adjustment 
with  the  depths  of  the  pulp-canal.  This  wire  forms  a  pattern  which  is 
reproduced  in  iridio-platinum  wire  from  No.  13  to  15  gauge,  which  is 
annealed  and  flattened  so  that  a  portion  of  it  will  present  a  flat  surface 
to  the  backs  of  the  canines,  and  the  transverse  portion  flattened  to  rest 
upon  the  backs  of  the  incisors  between  the  pins.  The  wire  is  bent  to 
the  conformation  of  the  brass  wire  pattern  (Fig.  838  ). 

The  caps  over  the  root-faces  are  loosened,  returned  to  position,  and  tlie 
iridio-platinum  bar  set  in  position.  The  wall  holding  the  porcelain  fac- 
ing is  applied,  and  the  perpendicular  arms  of  the  flattened  wire  perfora- 
ted for  the  passage  of  the  pins  of  the  canine  crowns.  The  wall  is  removed, 
the  bar  is  cemented  to  the  caps,  and  these  and  the  bar  withdrawn  from 
the  model  invested  and  soldered  with  the  minimum  of  pure  gold.  The 
piece  and  teeth  are  boiled  in  a  1 :  3  sulphuric-acid  solution.  The  bar 
caps  are  set  in  position  on  the  cast.  The  teeth  are  returned  to  the  plas- 
ter wall,  the  pins  of  the  canine  crowns  passing  through  the  perforations 
in  the  bar.  The  pins  of  the  incisor  crowns  are  bent  over  the  bar,  hold- 
ing each  tooth  in  position.  The  wire  may  be  grooved  or  notched  at  the 
site  of  the  pins  to  form  retaining  slots.  The  piece  is  now  carefully 
lifted  from  the  cast  and  prepared  for  the  application  of  the  porcelain 
(Fig.  839  ). 

Depressions  are  made  in  a  fire-clay  slab  which  shall  support  the  bars 
and  the  teeth.  Porcelain  body,  made  into  a  paste  with  water,  is  ap- 
plied, giving  a  contour  in  consonance  with  the  articulation  and  the  con- 
tact with  the  soft  tissues.     The  body  is  applied  as  the  second  body  of  a 


774 


AN  ASSEMBLAGE  OF   UNITED  CROWx\S. 


continuous-gum  piece.     It  s  set  on  the  supporting  slab,  and  the  porce- 
lain fused  in  a  proper  furnace,  as  with  continuous-gum  pieces. 

Gum  contour  of  similar  cases  may  be  restored  after  the  following 
method:  caps  are  fitted  to  the  prepared  'canine  roots  as  for  the  pre- 
ceding case.  A  pair  of  canine  facings  are  selected,  and  also  four  in- 
cisors of  the  continuous-gum  variety.  The  canine  caps  are  set  in  posi- 
tion and  an  impression  in  modelling  composition  taken,  which  presses 
firmly  upon  the  anterior  gum.  A  cast  of  investing  material,  and  next 
dies,  are  made,  and  an  iridio-platinum  plate  No.  32  is  swaged.  This 
plate  should  extend  upon  the  outer  alveolar  wall  as  high  as  it  is  desired 


Fig. 840 


Fig.  841 


to  have  the  artificial  gum.  At  its  palatal  aspect  the  edge  should  be 
formed  to  represent  about  the  usual  neck  sections  of  natural  incisors. 
The  lateral  edges  of  the  plate  should  overlap  or  lie  firmly  against  the 
sides  of  the  canine  collars,  to  which  it  is  united  by  means  of  a  small 
amount  of  24-carat  gold  as  solder.  The  piece  is  transferred  to  the 
mouth;  wire  posts  the  size  of  the  canals  are  fitted;  a  bite  and  next  a 
plaster  impression  are  taken.  A  cast  of  investing  material  is  made 
and  an  articulator  mounted. 

The  porcelain  teeth  are  now  adjusted  to  position;  the  incisors,  as 
though  for  the  usual  continuous-gum  operations,  and  their  stays  are 
fitted  to  the  teeth ;  a  support  and  posts  of  the  form  previously  described 
are  adapted,  over  which  the  pins  of  the  incisors  crowns  are  bent  (Fig. 
840).  More  investing  material  is  applied  to  cover  and  protect  the  porce- 
lain, and  the  teeth  are  united  to  the  bar  and  stays,  and  the  posts  to  the 
collars  by  means  of  the  minimum  of  24-carat  solder.  Fig.  841  shows 
labial  aspect.  The  porcelain  is  next  added.  Sufficient  body  is  applied 
to  give  the  desired  contour,  the  piece  is  baked,  and  the  gum  enamel  is 
then  added  and  a  final  baking  given. 


CHAPTER    XVI  11. 

HYGIENIC   RELATIONS  AND  CARE  OF  ARTIFICIAL   DENTURES. 
By  Charles  J.  Essig,  M.D.,.D.D.S. 

There  can  hardly  be  room  for  doubt  that  a  well-planned  and  prop- 
erly adjusted  artificial  denture  contributes  to  comfort  and  health,  and 
prolongs  the  life  of  the  individual  who  by  reason  of  premature  loss  of 
the  natural  teeth  finds  it  necessary  to  wear  one,  but  the  usefulness  of  the 
fixture  and  its  influence  on  the  mind  and  general  health  of  the  patient 
depend  very  largely  upon  the  manner  in  which  it  is  planned  and  con- 
structed. It  may  be  made  an  instrument  of  discomfort,  if  not  of  tor- 
ture, by  constructing  it  upon  a  faulty  impression.  It  may  entirely  fail 
to  meet  the  demands  of  a  masticating  apparatus  by  imperfect  articu- 
lation of  the  teeth.  It  may  so  interfere  with  speech,  through  want  of 
adhesion,  that  the  wearer  is  at  all  times  conscious  of  its  presence,  and  he 
is  thus  sometimes  forced  to  give  up  social  intercourse,  or  if,  as  in  the 
case  of  lawyers  or  clergymen,  professional  duties  require  the  individual 
to  address  audiences,  the  patient  feels  that  his  usefulness  is  abridged, 
and  mental  depression  and  departure  from  a  normal  standard  of  health 
follow. 

Prosthetic  dentistry  requires  in  its  successful  practice  good  judgment, 
artistic  taste,  and  a  high  degree  of  manipulative  ability.  No  two  cases 
are  ever  precisely  alike,  and  each  one  demands  careful  study  and  a 
definite  plan  of  procedure.  The  choice  of  material,  means  of  attach- 
ment, style  of  teeth,  and  the  arrangement  of  the  latter  to  ensure  the 
greatest  attainable  degree  of  efficiency  in  mastication  are  to  be  con- 
sidered. 

With  the  materials  at  the  present  time  within  the  reach  of  every 
prosthetic  dentist,  and  the  light  of  the  experience  of  other  workers  in 
that  branch  in  the  recent  past,  it  is  not  claiming  too  much  to  say  that 
artificial  dentures  may  be  so  constructed  and  adjusted  to  any  or  all 
mouths  as  to  restore  the  functions  of  mastication  and  speech,  as  well  as 
natural  appearance,  in  a  manner  but  little  short  of  absolute  perfection. 

The  pathological  conditions  incident  to  the  use  of  artificial  dentures 
may  be  local  or  systemic.  Many  morbid  phenomena  of  a  local  charac- 
ter may  be  observed  as  resulting  from  their  presence  in  the  mouth,  and 
marked  constitutional  disturbances  have  been  traced  to  the  same  causes. 

In  the  insertion  of  an  artificial  denture  a  foreign  body  is  introduced 
into  the  oral  cavity  which  may  act  as  an  irritant  to  tissues  and  organs 
with  which  it  comes  in  contact.  This  it  particularly  liable  to  occur  in 
all  lower  dentures,  on  account  of  the  pressure  being  confined  to  a  nar- 

775 


776  HYGIENIC  RELATIONS  OF  ARTIFICIAL   DFNTCRFS. 

row  area  and  the  muscles  and  integuments  being  attached  well  toward 
the  top  of  the  ridge,  as  in  the  case  of  the  buccinator  muscles;  painful 
abrasions  frecjuently  result  in  this  class  of  cases  soon  after  the  introduc- 
tion of  tile  fixture.  Abrasions  jjnxhiced  bv  unchie  pressure  of  the  edge 
of  a  plate  cause  an  amount  of  discomfort  and  sulfcring  entirely  out  of 
proportion  to  the  extent  of  the  injury.  To  avoid  a  continuance  of  this 
trouble  and  to  give  immediate  relief  the  patient  should  always  be  cau- 
tioned to  return  the  moment  the  presence  of  the  denture  becomes  painful. 

Artificial  dentures  are  held  in  place  by  atmospheric  pressure,  by  ad- 
hesion, by  clasps,  by  spiral  springs,  or  by  jjcrmanent  or  removable  at- 
tachments to  natural  teeth  or  roots.  Either  of  these  may  become  the 
cause  of  irritation  to  the  teeth  or  contiguous  parts.  In  the  case  of  clasps 
tiie  tendency  invariably  is  to  produce  morbid  phenomena,  and  this  ten- 
dency is  increased  or  lessened  by  the  character  of  the  materials  of  which 
they  are  made,  and  the  manner  in  which  the  clasps  are  adjusted  and 
the  parts  of  the  teeth  embraced  by  them. 

The  result  produced  ])y  clasping  natural  teeth  is  a  loss  of  tissues, 
either  through  caries,  mechanical  abrasion,  electro-chemical  action,  or  by 
the  joint  action  of  all  three.  The  rapidity  with  which  the  disintegrating 
process  advances  depends  largely  upon  the  quality  of  the  tooth-sub- 
stance, the  condition  of  the  oral  fluids,  the  size  and  form  of  the  clasp,  the 
portion  of  the  tooth  which  is  embraced  by  it,  and  the  material  of  which 
the  clasp  is  constructed. 

A  partial  lower  denture  must  be  secured  either  by  clasps  or  contact 
with  natural  teeth.  In  that  class  of  partial  lower  dentures  designed  to 
replace  the  second  bicuspids  and  molars  on  each  side  clasps  adjusted  to 
the  first  bicuspids  are  generally  employed:  caries  of  the  approximal 
surfaces  of  the  first  bicuspids  is  more  or  less  quickly  induced,  probably 
because  the  enamel  is  thin  at  that  point.  Incipient  caries,  produced  by 
clasps  at  the  positions  above  indicated,  manifests  itself  by  great  sensitive- 
ness of  the  tooth,  which  is  exceedingly  painful  when  exposed  to  extremes 
of  temperature  and  certain  kinds  of  food,  such  as  very  sweet  or  salt  arti- 
cles. Painful  mechanical  abrasions  are  frequently  caused  where  mere 
contact  with  natural  teeth  is  the  means  adopted  for  securing  stability  to 
partial  dentures.  Badly-fitting  clasps,  as  may  be  expected,  rapidly 
hasten  the  progress  of  caries  by  favoring  the  lodgement  between  the 
tooth  and  clasp  of  particles  of  food  mixed  with  the  oral  fluids,  which 
undergo  fermentative  decomposition  and  produce  agents  destructive  to 
the  enamel  and  dentine. 

Clasps  should  be  accurately  fitte»l  to  the  broadest  part  of  the  tooth, 
which  is  usually  found  at  or  near  the  masticating  portion  of  the  crown, 
and  never  at  the  necks  of  the  tooth.  They  should  not  be  allowed  to 
impinge  upon  the  gum,  as  recession  of  that  tissue  and  exposure  of  the 
cementum,  with  subsequent  softening  and  caries,  will  almost  certainly 
supervene. 

While  the  result  of  observation  as  to  the  effect  of  clasps  upon  the 
natural  teeth  is  undoubtedly  in  all  cases  imfavorable,  yet  there  are 
many  instances  in  which  clasps  are  indispensable,  and  their  capacity 


CLEANING   OF  ARTIFICIAL  DENTURES.  777 

for  doing  harm  may  be  very  greatly  reduced  by  adjusting  them  with 
accuracy  to  the  most  convex  portions  of  the  teeth,  avoichng  impinge- 
ment upon  the  necks  and  cementum. 

It  has  been  observed  that  chisps  exert  an  influence  upon  teeth  vary- 
ing in  degree  accortUng  to  the  condition  of  the  oral  fluids  and  the  kind 
of  metal  cf  which  they  are  made.  Silver  clasps  have  been  found  to 
exert  a  much  more  rapid  disintegrating  influence  than  those  made  of 
gold.  Dentures  with  clasps  or  attachments  made  of  platinum  or  iridio- 
platinum  act  more  injuriously  than  the  same  appliances  fitted  with  gold 
clasps.  These  differences  in  the  efi^ects  of  the  metals  upon  the  teeth 
are  probably  due  to  a  galvanic  current  between  the  tooth-structure 
and  the  metal  forming  the  plate,  aided  by  certain  conditions  of  the  oral 
fluids. 

Silver  and  platinum  should  not  be  used  in  the  formation  of  clasps,  or 
indeed  for  any  purpose  which  demands  contact  with  tooth-structure.  It 
has  been  observed  that  teeth  in  contact  with  a  platinum  wire  employed 
as  a  means  of  retention,  their  positions  having  been  changed  in  the  cor- 
rection of  irregularities,  exhibited  erosions  in  a  comparatively  short 
time  after  its  application. 

An  example  of  the  action  of  silver  upon  the  natural  teeth  was  observed 
a  number  of  years  ago  in  the  case  of  a  man  who  had  in  an  election 
fracas  sustained  a  severe  fracture  of  the  jaw.  When  he  presented  him- 
self for  treatment  at  the  college  cKnic,  nearly  a  year  after  the  injury  had 
been  received,  it  was  found  that  the  jaw  was  in  three  parts,  no  union 
having  taken  place.  He  had  received  a  blow  from  some  heavy  instru- 
ment upon  the  mental  portion  of  the  bone ;  the  fractures  were  on  each 
side  between  the  first  and  second  bicuspids.  The  individual,  for  some 
reason  best  known  to  himself,  had  been  obliged  to  remain  in  conceal- 
ment for  several  weeks  after  the  injury,  during  which  time  he  received 
no  surgical  treatment  whatever.  The  appearance  of  the  lower  part  of 
the  face  was  greatly  changed  by  the  displacement  of  the  disunited 
parts  of  the  jaw,  and  mastication  was  impossible.  As  a  temporary  or 
palliative  remedy  for  the  latter  difficulty  a  dental  surgeon  had  fitted  a 
bar  of  stout  half-round  silver  wire  entirely  around  the  lower  teeth,  so  as 
to  hold  the  parts  in  juxtaposition  and  restore  the  articulation  of  the 
teeth.  The  individual  had  not  worn  the  fixture  many  weeks  before 
the  posterior  surfaces  of  the  second  molars,  where  the  brunt  of  the  force 
v/as  borne,  became  unbearably  sensitive.  An  examination  showed 
deep  grooves  in  these  teeth,  rapidly  approaching  the  pulps.  k.s  the 
neighboring  teeth  appeared  of  good  quality  and  entirely  free  of  caries, 
the  abrasion  on  the  second  molars  was  probably  due  to  galvanic  action 
between  the  silver  support  and  the  tooth-structure. 

The  wearing  of  artificial  dentures  at  night  is  a  subject  upon  which 
there  is  much  difference  of  opinion.  It  may  be  advisable  in  the  case 
of  a  full  denture  for  either  or  both  jaws,  particularly  in  the  beginning 
of  its  use  by  the  patient,  for  its  presence  in  the  mouth  except  at  such 
times  as  it  has  been  removed  for  purposes  of  cleansing  enables  the 
patient  to  more  speedily  become  accustomed  to  its  use. 


778  HYGIENIC  nELATlOyS  OF  ARTIFICIAL  DENTURES. 

There  is  hardly  room  for  doubt,  however,  that  disintegration  of  the 
tooth-substance  when  chisps  are  used  is  hkely  to  proceed  much  more 
rapidly  where  the  piece  is  worn  continuously;  besides,  careful  observa- 
tion has  shown  that  at  night  the  oral  secretions  assume  a  slightly  acid 
character.  This  has  been  demonstrated  particularly  in  patients  sub- 
ject to  enamel  erosion  by  carefully  testing  the  oral  secretions  with  litmus 
after  waking  and  before  the  salivary  fluids  have  started  their  usual  flow. 

If  the  necks  of  the  teeth  are  highly  sensitive  or  there  is  well-marked 
tendency  to  softening  or  erosion  of  the  tooth-structure,  the  patient 
should  be  directed  to  remove  the  plate  each  night  before  retiring,  and 
to  apply  to  the  affected  teeth,  after  thoroughly  cleansing,  a  small  quan- 
tity of  precipitated  chalk,  lime-water,  or  milk  of  magnesia. 

Too  much  stress  cannot  be  laid  upon  the  necessity  for  cleanliness, 
and  every  patient  who  wears  a  denture  secured  by  clasps  should  be  par- 
ticularly instructed  in  the  means  of  removing  the  deposits  which  are 
usually  found  on  the  inside  surfaces  of  the  clasps.  This  is  not  generally 
well  done  by  patients  with  the  tooth-brush  alone,  so  that  a  piece  of  soft 
wood  armed  with  fine  pumice  is  necessary  to  do  it  thoroughly,  and  the 
addition  of  aqua  ammonia  is  efficacious. 

Patients  suflfering  from  any  chronic  conditions  of  the  system  which 
are  likely  to  be  accompanied  with  acidity  of  the  oral  fluids  must  be  cau- 
tioned to  exercise  the  most  scrupulous  care  in  cleansing  the  artificial 
denture;  and  this  caution  is  particularly  demanded  when  partial  den- 
tures are  worn.  In  these  cases  lime-water  and  bicarbonate  of  sodium 
are  recommended  as  alkaline  mouth-washes,  which  by  neutralizing 
the  acid  condition  of  the  fluids  are  often  eflfective  in  preventing  sensi- 
tiveness and  the  tendency  to  softening  of  the  tooth-substance. 

In  the  mouths  of  young  persons  whose  teeth  show  unmistakable 
evidences  of  a  tendency  to  rapid  decalcification  clasps  should  never  be 
employed;  and  this  is  a  matter  to  be  decided  by  the  dentist  himself 
even  when  the  patient  expresses  the  strongest  preference  for  the  small 
plate  attached  by  clasps  and  an  equally  forcible  objection  to  the  larger 
atmospheric  plate. 

Of  the  hygienic  relations  of  spiral  springs,  which  as  a  means  of  re- 
taining artificial  dentures  antedated  all  other  devices  now  in  use,  very 
little  need  be  said,  since  the  appliances  are  no  longer  used  except  in 
rare  cases  of  edentulous  mouths  complicated  with  cleft  palate,  w^herein 
adhesion  would  be  impossible.  Three  principal  objections  may  be 
urged  against  the  employment  of  spiral  springs  for  the  retention  of 
ordinary  dentures,  as  follows:  their  Hability  to  chafe  and  abrade  the 
delicate  mucous  membrane  lining  of  the  cheek,  the  tendency  of  one  or 
the  other  to  break,  and  the  difficulty  of  thoroughly  cleaning  them. 

The  materials  used  in  the  construction  of  artificial  dentures,  other 
conditions  being  ec|ual,  do  not  differ  to  any  great  extent  in  their  effect 
upon  the  tissues  with  which  they  come  in  contact.  On  the  other  hand, 
the  frequency  and  extent  of  oral  irritation  associated  w^th  the  w^earing 
of  artificial  dentures,  irrespective  of  materials  employed,  varies  with  dif- 
ferent individuals.     It  is  not,  however,  denied  that  modifications  of 


INFLAMMATION  UNDER  RUBBER  DENTURES.  779 

that  portion  of  the  surface  of  the  mouth  covered  by  the  artificial  den- 
ture is  more  frequent  in  cases  where  rubber  and  celluloid  are  worn. 
The  author  has  always  believed  that  the  real  cause  of  the  inflammatory 
conditions  so  generally  attributed  to  vegetable  bases  will  be  found  in 
the  following  conditions:  (1)  the  non-conducting  quality  of  the  sub- 
stances; (2)  the  rough  condition  of  the  surfaces  of  the  majority  of  rub- 
ber or  celluloid  dentures,  due  to  carelessness  or  want  of  skill  in  construc- 
tion; (3)  want  of  care  on  the  part  of  the  wearer  in  not  frequently  cleans- 
ing the  denture  of  deposits  of  food  and  secretions  of  the  mouth,  which 
are  likely  to  undergo  chemical  change  by  long  confinement  in  contact 
with  the  tissues,  and  thus  become  irritants.  Either  one  or  all  of  the 
conditions  named  may  cause  inflammation  of  the  mucous  membrane, 
but  always,  so  far  as  the  author's  observation  has  gone,  limited  to  the 
area  covered  by  the  plate.  Similar  conditions  are  frequently  noticed 
when  the  dentures  were  of  gold  or  silver,  but  always  in  cases  where  the 
plate  was  seldom  removed  or  cleansed.  And  if  the  trouble  referred  to 
is  more  common  in  rubber  or  celluloid  dentures  than  where  metallic 
plates  are  worn,  there  are  doubtless  more  conditions  favoring  such  a 
result  in  the  former  than  are  found  in  the  latter;  and  the  facts  that  the 
symptoms  are  not  constant,  and  that  by  far  the  greater  number  of 
mouths  in  which  rubber  or  celluloid  is  worn  are  not  in  the  least  aftected 
by  it,  w^ould  seem  to  confirm  the  view  that  the  inflammation  referred 
to  is  due  to  contact  with  irritating  products  of  food  and  secretions,  and 
that  these  are  equally  active  in  all  dentures,  irrespective  of  the  material 
of  which  the  dentures  are  made. 

Rubber  sore  mouth  as  described  in  the  American  System  of  Dentis- 
try, if  met  with  at  all,  must  be  exceedingly  rare,  and  the  "rubber  sore 
mouth"  which  passes  the  stage  of  redness  and  slight  tenderness  and  ex- 
tends to  the  tonsils  and  walls  of  the  pharynx,  with  the  parts  greatly 
swollen  and  painful,  rendering  the  wearing  of  the  plate  impossible  for 
the  time  and  the  formation  of  abscesses,  the  author  has  never  seen. 

Acute  inflammatory  conditions  of  the  mouth  which  appear  with  some 
degree  of  suddenness  may  often  be  traced  to  persistent  efforts  on  the 
part  of  the  patient  to  obtain  adhesion  through  atmospheric  pressure 
in  a  badly-fitting  denture  by  powerful  suction  of  the  tongue  in  the 
effort  to  exhaust  the  air  from  the  chamber :  violence  of  this  kind,  aided 
by  the  other  unfavorable  conditions  referred  to,  may  cause  occlusion 
of  mucous  follicles  and  the  usual  inflammation  resulting  from  inter- 
ruption of  the  secretions;  but  it  would  be  manifestly  wrong  to  class 
such  conditions  under  the  heading  of  "Rubber  Sore  Mouth." 

The  great  majority  of  cases  of  local  irritation  associated  with  the 
wearing  of  dentures  are  not  usually  cases  calling  for  the  exhibition  of 
drugs,  but  as  the  rules  of  hygiene  extend  to  all  conditions  wdiich  may 
cause  departure  from  a  normal  standard  of  health,  whether  local  or 
general,  the  first  step  in  the  treatment  of  so-called  "rubber  sore  mouth" 
should  be  an  examination  of  the  plate  to  determine — 1st,  if  there  is  accu- 
racy of  adaptation;  2d,  is  the  surface  of  the  denture  smooth  enough, 
and  in  proper  condition  to  be  constantly  worn  in  contact  with  the  deli- 


780  UYCIKNIC  RKLATIONS  OF  ARTIFICIAL   DFSTIJRFS. 

cate  tissues  of  the  mouth  ?  3d,  is  the  denture  free  of  deposits  of  food  and 
secretions?  A  cure  will  usually  be  promptly  effected  hy  the  fulfilment 
of  the  three  conditions  niimetl. 

Rubber  dentures  favor  the  dejiosition  of  material  composed  of  food 
and  mucus  secreted  from  the  follicles  of  the  tissues  covered  by  the 
plate,  which  often  escapes  the  observation  of  the  patient  and  is  always 
difficult  to  remove  thoroughly.  The  patient  should  be  carefully  in- 
structed as  to  the  best  means  of  keeping  the  denture  free  from  this  de- 
posit, which  will  consist  in  the  frequent  use  of  a  strong  solution  of  soda,  in 
which  the  plate  should  occasionally  remain  immersed  over  night, 
and  when  the  deposit  is  thoroughly  softened  by  the  soda  solution,  the 
careful  use  of  the  tooth-])rush  armed  with  soap  and  tooth-powder. 
Salivary  calculus,  which  often  deposits  in  large  Cjuantities  on  lower 
plates,  may  be  removed  by  immersing  the  denture  over  night  in  vinegar 
and  water;  but  if  crowns  of  natural  teeth  have  been  reset  on  metallic 
plates,  the  salivary  calculus  must  be  removed  by  instruments,  as  any 
form  of  acid  would  dissolve  the  enamel  and  ruin  the  teeth. 

If  a  chronic  state  of  inflammation  of  the  surface  covered  by  the  den- 
ture has  become  established  by  violation  of  the  conditions  essential  to 
maintenance  of  a  normal  state  of  the  oral  tissue,  local  applications  of 
phenol  sodi([ue,  thymozone,  or  listerine,  diluted  in  the  proportion  of 
one  part  of  the  remedy  to  three  or  four  of  water,  will  generally  relieve 
the  tissues  of  redness  and  tenderness. 

In  cases  of  long  standing  and  unusual  severity  zinci  sulphas  in  solu- 
tion, in  the  strength  of  gr.  j  or  ij  to  f  oSS  of  water,  will  be  found  of  great 
service  as  an  application  to  the  inflamed  parts. 

Some  authorities  state  that  chronic  stages  of  so-called  "rubber  sore 
mouth"  are  curable  only  by  the  substitution  of  a  denture  made  upon 
metal.  Such  cases  the  author  has  never  met  W'ith,  and  he  believes  that 
careful  fulfilment  of  the  conditions  of  precision  of  adaptation,  smooth- 
ness of  surface  in  contact  with  the  tissues,  and  absolute  cleanliness  will 
generally  be  found  sufficient  to  restore  the  mouth  to  a  normal  state. 

Excessive  absorption  of  the  alveolar  ridge,  ending  in  the  entire  ob- 
literation of  any  semblance  of  a  ridge,  is  extremely  rare,  and  not  a 
single  instance  of  the  kind  has  been  met  \\\i\\  by  the  author  in  his  entire 
practice.  The  few  cases  of  absorption  of  the  anterior  portion  of  the 
ridge  which  have  come  under  his  notice  have  been  mouths  in  which 
metal  plates  have  been  worn.  This  phenomenon  has  been  attributed 
to  the  poisonous  action  of  vermilion  used  in  dental  rubbers  as  a  pig- 
ment; imperfect  vulcanization,  causing  porosity  of  the  plate,  thus 
favoring  the  absorption  of  secretions  or  the  growth  of  micro-organisms 
on  that  portion  of  the  plate  in  contact  with  the  mucous  membrane; 
but  it  is  quite  probable  that  excessive  absorption  of  the  alveolar  ridge 
is  an  inherited  tendency.  The  author  has  observed  that  condition  in 
more  than  one  member  of  the  same  family,  where  the  anterior  portion 
of  the  alveolar  ridge  has  quite  disappeared,  while  the  ridge  in  the  pos- 
terior part  of  both  mouths  is  unusually  broad  and  prominent.  It  is 
also  most  commonly  caused  in  this  portion  of  the  mouth  by  the  impact 


INFLAMMATION  UNDER  RUBBER  DENTURES.  781 

of  the  lower  anterior  natural  teeth,  the  posterior  teeth  of  the  mandible 
liavinfi-  been  lost,  and  the  artificial  denture  in  the  upper  jaw  sustaining 
in  the  front  the  whole  force  of  mastication. 

Pure  vermilion,  in  combination  with  rubber,  is  not  likely  to  produce 
deleterious  effects  when  worn  in  the  mouth,  nor  is  it  probable  that  this 
compound  can  be  decomposed  chemically  and  converted  into  a  poison- 
ous salt  of  mercury  by  mere  contact  with  the  saliva. 

The  mechanical  dentist  will,  however,  do  well  to  avoid  the  use  of 
nitrohydrochloric  acid  in  removing  tin-foil  from  the  surface  of  unfin- 
ished vulcanite  dentures.     (See  chapter  on  Metallurgy:    Mercury.) 

Regarding  the  presence  of  free  mercury  in  rubber  before  or  after 
vulcanizing,  Prof.  Austin  stated  that  the  researches  of  Prof.  Johnston 
with  the  microscope,  and  of  Prof.  Mayer  by  chemical  analysis,  failed 
to  discover  the  slightest  trace  in  samples  of  that  which  had  been  used  for 
several  years.  Prof.  Wildman  observed  that  sulphur  sublimed  during 
vulcanization,  but  did  not  find  the  smallest  trace  of  free  mercury. 
Prof.  Austin  further  stated  that  he  never  during  his  entire  experience 
with  indurated  rubber  as  a  base  for  artificial  dentures  detected  the 
slightest  particle  of  metallic  mercury  on  the  surface  of  any  finished 
piece. 

In  the  belief  that  mercuric  sulphide  (vermilion)  may  be  the  cause  of 
the  different  phases  of  so-called  rubber  sore  mouth,  the  substitution  of 
black  for  red  rubber  has  been  recommended  as  a  means  of  overcoming 
the  tendency  to  excessive  tenderness  of  the  mucous  membrane  covered 
by  the  plate.  Black  rubber  is  but  a  doubtful  improvement  upon  the 
red  variety  so  far  as  influence  on  the  health  of  the  tissues  is  concerned. 
As  it  contains  lampblack  as  a  pigment,  it  is  uncertain  whether  it  is 
more  dense  and  less  liable  to  absorb  secretions.  The  best  quality  of 
rubber  for  dental  purposes,  the  one  affording  the  greater  density  of 
surface,  is  that  which  is  composed  simply  of  caoutchouc  48  parts,  sul- 
phur 24  parts,  without  any  pigment  whatever.  This  rubber  is  of  a 
dark  drab  color  and  it  differs  so  widely  from  the  color  of  the  tissues  that 
it  has  never  been  employed  to  any  great  extent  in  prosthetic  dentistry. 

Vulcanizable  rubbers,  of  whatever  composition,  require  great  care 
both  in  investing  and  indurating.  Campbell,  the  inventor  of  the  "New 
Mode  Heater  for  Rubber  and  Celluloid  Work,"  demonstrated  that  the 
only  way  to  obtain  fine  texture  and  density  of  surface  in  rubber  and 
celluloid  is  to  expose  them  to  low  temperature,  dry  heat,  and  contact 
with  metallic  surfaces.^  This  produces  a  harder  rubber,  less  porous 
and  less  liable  to  absorb  the  secretions  than  can  be  obtained  by  contact 
with  plaster,  or  indeed  by  any  other  means;  but  where  the  modus  oper- 
andi suggested  by  Drs.  Campbell  and  Evans  is  practised,  the  prelim- 
inary "waxing"  of  the  case  must  be  done  with  such  precision  that  the 
surface  thus  obtained  need  not  be  subsequently  disturbed  by  the 
scraper.      (See  chapter  on  Vulcanite  Work.) 

^  The  manufacturers  of  rubber  articles  of  jewelry  and  ornamentation  long  since  abandoned 
the  use  of  steam  as  a  heating  medium  and  plaster  as  an  investment. 


782  HYGIENIC  RELATIONS  OF  ARTIFICIAL  DENTURES. 

The  theory  presented  by  Dr.  G.  V.  Blaek,  that  the  sore  mouth  pro- 
duced by  artificial  dentures  is  (kie  to  the  growth  of  certain  fungi  which 
elaborate  an  acid  secretion  which  acts  as  an  irritant  to  the  mucous  mem- 
brane, is  probably  correct.  He  asserted  that  he  found  these  fungi  upon 
the  surfaces  of  all  plates  without  regard  to  the  material  of  which  they 
were  constructed,  but  in  the  greatest  number  upon  the  surfaces  of  vul- 
canite dentures;  which  he  attributed  to  the  fact  that  the  irregularities 
and  roughness  of  the  surfaces  of  such  plates  afforded  lodging-places 
where  they  rapidly  developed  on  account  of  the  greater  (Hfficulty  in 
thoroughly  cleansing  them,  and  he  regards  absolute  cleanliness  as  a 
complete  protection  from  inflammation. 

Prof.  E.  C.  Kirk  stated,  as  the  result  of  repeated  tests  of  the  mucous 
secretion  in  cases  of  sore  mouth  associated  with  the  rubber  denture, 
that  the  mucus  in  such  cases  generally  showed  an  alkaline  reaction  as  it 
was  eliminated;  and  he  suggests  the  possibility  that  alkaline  sulphides 
might  be  eliminated  to  a  sufficient  extent  to  exert  a  slight  solvent  action 
upon  the  mercuric  sulphide  of  the  plate,  and  thus  form  an  active  salt 
of  mercury.  But  this  theory  seems  to  be  at  variance  with  the  more 
practical  reasoning  and  experience  of  many  others  who  have  given  much 
thought  and  attention  to  the  subject.  Prof.  Kirk's  suggestion,  how- 
ever, that  the  non-conducting  quality  of  the  vegetable  bases  plays  an 
important  part  in  the  production  of  every  kind  of  inflammatory  action 
undoubtedly  carries  with  it  much  force,  for,  as  he  states,  "the  effect  on 
the  tissues  continually  enclosed  by  the  non-conducting  plate  is  to  main- 
tain a  hyperaemic  condition,  with  slight  increase  of  temperature:  this 
in  addition  to  the  pressure,  which,  if  it  does  not  result  in  inflammation, 
is  a  source  of  irritation  sufficient  to  bring  about  greatly  increased  func- 
tional activity  of  the  cells  of  the  parts." 

It  was  at  one  time  thought,  and  so  claimed  by  many  of  its  advocates, 
that  the  substitution  of  celluloid  for  rubber  dentures  would  prove  an 
effective  remedy  in  cases  of  sore  mouth;  but  that  material  is  open  to 
the  same  objections  as  rubber,  and  to  a  greater  degree  in  consequence 
of  the  sponginess  of  surface  incident  to  the  evaporation  of  camphor. 

Partial  artificial  dentures  immovably  attached  to  one  or  more  natural 
teeth  or  roots  of  teeth,  or  the  attachment  of  several  crowns  to  one  or 
more  roots  as  in  bridge-work,  present  many  points  for  consideration 
from  a  hygienic  standpoint.  The  operation  of  substituting  an  artificial 
crown  for  a  natural  one  should  not,  if  properly  performed,  affect  the 
integrity  of  any  of  the  surrounding  tissues,  ami  yet  if  the  work  is  ill- 
fitting  and  done  in  a  slovenly  manner,  with  the  cap  or  ferrule  extend- 
ing so  far  under  the  free  margin  of  the  gum  as  to  impinge  upon  the 
alveolar  border  of  the  socket,  persistent  irritation  may  be  established 
which  can  only  end  in  disorganization  of  connective  tissue  and  loss  of 
the  root  if  the  cause  be  not  removed.  The  experience  of  the  author  has 
been  that  roots  upon  which  artificial  crowns  have  been  fixed  are  less 
liable  to  pericemental  inflammation  and  abscess  than  are  dcAitalized 
teeth  with  natural  crowns,  the  greater  success  in  the  treatment  of  the 
crownless  root  being  probably  due  to  its  accessibility  and  the  better 


BRIDGE-WORK.  783 

opportunity  which  undoubtedly  exists  of  filUng  the  latter  with  thorough- 
ness to  the  full  extent  of  the  canal.  The  fact,  too,  of  restoring  occlusion, 
whereby  roots  are  brought  into  use,  helps  to  keep  them  in  a  healthy 
condition,  and  prevents  their  gradual  extrusion  and  premature  loss 
from  the  alveoli. 

As  is  well  known,  there  are  a  variety  of  methods  of  setting  artificial 
crowns  to  roots.  Any  one  of  these  methods,  if  lacking  in  the  element 
of  precision  of  adjustment,  may  favor  the  estabHshment  of  patho- 
logical conditions.  The  Richmond  crown,  properly  so  called,  with  an 
accurately  fitted  cup  or  ferrule,  is  perhaps  less  liable  to  cause  irritation  to 
the  surrounding  tissues  than  any  of  the  methods  of  crown-setting  in  use. 

The  worst  results  have  been  noticed  in  that  class  of  crowns,  without 
caps  or  ferrules,  in  which  the  attachment  to  the  root  is  secured  by 
means  of  amalgam.  If  the  latter  is  allowed  to  project  at  the  point  of 
union  of  the  cro^^  n  and  root,  it  soon  becomes  exceedingly  irritating  to 
the  margins  of  the  gum — a  condition  marked  by  redness,  tumefaction, 
and  a  tendency  to  bleed,  particularly  in  the  recumbent  position  at  night, 
and  a  nocturnal  flow  of  saliva  similar  to  that  noticed  in  pyorrhoea  al- 
veolaris  becomes  established.  The  only  remedy  for  chronic  dental 
irritation  due  to  this  cause  is  the  removal  of  the  crowns  and  the  sub- 
stitution of  others  which  are  not  dependent  upon  amalgam  as  a  means 
of  attachment. 

Bridge-work,  which  consists  of  the  bridging  of  interdental  spaces  by 
one  or  more  crowns  fastened  together  and  attached  to  natural  teeth  or 
roots,  frequently  causes  pathological  conditions  from  a  want  of  care  and 
exactness  in  their  construction,  and  by  requiring  two  or  more  roots  to 
sustain  an  amount  of  force  in  mastication  greatly  in  excess  of  that  for 
which  they  were  intended.  As  a  result  of  the  excessive  strain  to  which 
they  are  subjected  under  such  conditions,  fracture  of  the  roots,  chronic 
inflammation  of  their  pericemental  membranes,  abscesses,  or  pro- 
tracted tenderness  may  occur,  either  of  these  being  sufficient  to  seriously 
interfere  with  mastication  and  render  the  denture  useless. 

Cases  of  serious  local  irritation  from  unusual  causes  are  occasionally 
met  with  in  so-called  bridge-work.  The  author  once  met  with  a  case 
in  which  a  bridge  had  been  constructed  for  the  purpose  of  replacing 
two  right  upper  bicuspids.  The  attachment  consisted  of  a  wire  of 
ordinary  18-carat  gold  fastened  with  amalgan  in  the  canine  and  first 
molar,  both  of  which  were  devitalized.  The  wire  had  gradually 
yielded  under  the  pressure  of  mastication  until  the  necks  of  the  two 
artificial  teeth  had  become  imbedded  in  the  gum  tissues,  which  were 
so  much  swollen  that  only  the  points  of  the  porcelain  teeth  were  visible. 
The  general  health  of  the  patient  was  greatly  affected  by  the  persistent 
irritation  caused  by  the  displaced  bridge :  no  time  was  therefore  lost  in 
removing  it.  This  was  done  with  the  greatest  relief  to  the  patient,  the 
tissues  returning  within  a  few  days  to  their  normal  condition. 

Although  skilful  and  experienced  bridge-workers  generally  plan  and 
construct  dentures  of  this  class  with  special  reference  to  complete 
cleanliness,  yet  it  is  doubtful  whether  all  parts  of  the  best  of  them  can  be 


784  HYGIENIC  RELATIOyS  OF  ARTIFICIAL  DENTURES. 

reached  by  the  tooth-brush  as  thoroughly  as  is  the  case  with  the  ordinary 
removal)le  denture.  In  many  cases  the  irritation  in(hiced  by  the  impac- 
tion of  food-debris  and  fermenting  secretions,  and  the  unusual  strain 
upon  roots  of  diseased  teeth,  will  cause  hypertrophy  of  the  surrounding 
tissues  or  rapid  loosening  from  absorption  of  their  alveolar  borders. 
These  conditions  are  always  accompanied  by  more  or  less  vitiation  of 
the  secretions  of  the  mouth  and  foulness  of  breath,  constituting  in  many 
cases  potent  arguments  against  their  introduction. 

Of  the  different  methods  of  constructing  this  class  of  dentures,  the 
removable  bridge  is  probably  open  to  fewer  objections  than  any  of  the 
other  forms;  yet  even  that  plan  re(|uires  good  judgment  in  determin- 
ing the  capability  of  teeth  or  roots  to  sustain  the  extraordinary  strain 
to  which  they  must  necessarily  be  subjected,  and  the  greatest  skill  and 
care  in  the  construction  and  adjustment  of  the  different  parts  of  the 
fixture. 

The  introduction  of  immovable  "bridge"  dentures  has  undoubtedly 
in  a  great  many  cases  caused  so  much  discomfort  and  irritation  to  sur- 
rounding tissues  as  to  render  mastication  almost  impossible,  and  it  is 
doul)tful  whether  extensive  operations  of  this  class,  considered  from 
their  hygienic  relations,  are  as  satisfactory  as  properly  planned  and 
constructed  removable  dentures  retained  in  position  by  atmospheric 
pressure. 

Care  in  cleansing  artificial  dentures  of  whatever  form,  size,  or  mater- 
ial is  of  the  utmost  importance.  The  cleansing  should  be  performed 
immediately  after  eating,  and  particularly  before  retiring  for  the  night. 
If  this  be  not  done  with  some  degree  of  thoroughness,  debris  of  food 
mixed  with  saliva  and  mucus  forms  an  adherent  mass  upon  the  plate 
which  undergoes  fermentation  and  decomposition,  with  the  result  of 
irritating  the  mucous  membrane  and  producing  a  general  inflammation 
of  the  oral  cavity,  and  the  irritation  of  the  oral  secretions  may  cause 
serious  derangement  of  the  digestive  function. 

It  is  the  duty  of  the  dentist  to  instruct  his  patient  as  to  the  import- 
ance of  cleanliness  and  in  the  proper  means  by  which  that  result  may  be 
accomplished.  The  thorough  cleansing  of  an  artificial  denture,  al- 
though appararently  a  simple  operation,  seems  to  be  a  matter  of  great 
difficulty  to  the  majority  of  patients,  and  but  few  are  capable  of  main- 
taining a  faultless  condition  of  their  dentures;  yet  the  tooth-brush 
armed  with  soap  and  ordinary  tooth-powder  is  quite  sufficient  to  main- 
tain a  clean  and  highly  polished  surface.  The  patient  should  be  cau- 
tioned against  the  danger  of  bending  partial  loAver  dentures  of  gold  or 
other  metals  by  grasping  them  with  too  much  force  while  brushing,  and 
in  the  case  of  vulcanite  dentures  to  avoid  "boiling  them  out"  in  hot 
water.  ^Nlany  individuals  who  have  previously  worn  gold  dentures 
resort  to  that  means  of  ridding  the  fixture  of  deposits  of  food,  etc. 
which  have  found  a  lodgement  under  the  teeth  and  behind  the  backing. 
The  author  has  met  with  several  instances  where  recently  constructed 
vulcanite  dentures  have  been  completely  ruined  within  a  short  time  of 
their  completion  by  immersion  in  boiling  water. 


FIXED   BRIDGES.  785 

In  the  construction  of  metallic  plates  for  partial  dentures  the  plate 
should  be  accurately  fitted  around  remaining  natural  teeth,  so  that  there 
will  be  no  spaces  between  the  plate  and  the  teeth  to  admit  of  pinching 
of  the  gum  between  the  edge  of  the  former  and  the  neck  of  the  tooth; 
and  where  a  point  of  the  plate  extends  between  two  teeth — as,  for  in- 
stance, the  central  incisors — such  projection  must  be  made  to  fit  the 
space  accurately,  or  it  will  be  certain  to  cause  inflammation  which  may 
result  in  permanent  impairment  of  the  teeth.  Defects  of  this  kind 
may  be  corrected  by  soldering  an  addition  to  the  edge  of  the  plate  in 
order  to  bring  it  almost  in  contact  with  the  teeth,  or  else  by  cutting 
away  the  plate  so  freely  that  its  distance  from  the  teeth  will  preclude  the 
danger  of  pinching  the  tissues. 

50 


CHAPTER    XIX. 

PALATAL  MECHANISM 

By  Rodrigues  Ottolengui,  M.D.S.* 

CLEFT  PALATE. 

Cleft  palate  may  be  divided  into  two  classes — acquired  and  con- 
genital. Acquired  lesions  include  all  of  those  cases  where  the  indi- 
vidual, having  been  born  with  a  normal  oral  cavity,  later  in  life  suffers 

Fig.  842 


a  division  of  the  hard,  or  of  the  soft  palate,  or  of  both.  This  unfortu- 
nate mischance  may  be  caused  by  an  accident;  or  it  may  be  the  sequence 
of  disease,  usually  syphilis;  or  the  result  of  a  surgical  operation  for  the 
removal  of  malignant  growths. 

The  acquired  lesions  may  be  very  slight,  as  a  mere  perforation  of  the 
hard  palate,  or  they  may  be  most  extensive  in  character,  comprising  a 

I  I  am  indebted  to  Dr.    Norman  W.  Kingsley  for  the  use  of  his  Krge  collection  of  models  from 
■which  to  choose  for  illustrations,  as  well  as  for  the  pri\-ilege  of  referring  to  cases  from  his  practice 
in  order  more  clearly  to  expound  the  theories  and  principles  set  forth. 
786 


p.  I  LA  TA  L  MECHANISM. 


787 


complete  cleft  of  the  hard  and  soft  palate,  with  total  destruction  of  the 
vomer  and  turbinated  bones,  as  well  as  the  bridge  of  the  nose,  and 
sometimes  the  nose  itself.  Such  an  extreme  case,  of  course,  would  only 
have  its  origin  in  disease.  Betw^een  the  two  extremes  .cited  an  endless 
variety  of  cases  are  found,  many  of  which  will  tax  the  ingenuity  of  the 
operator  to  its  utmost.  The  conditions  which  may  follow  upon  unsuc- 
cessful surgical  operations  frequently  add  to  the  complexities  of  cases. 
Fig.  842  shows  a  case,  the  absence  of  the  uvuLne,  and  the  adhesions 
, which  have  united  the  posterior  borders  of  the  divided  soft  palate  to 
the  pharyngeal  wall,  making  this  case  readily  distinguishable  from  one 
of  congenital  origin. 

Fig.  843 


Nevertheless,  whether  the  acquired  lesion  be  of  small  or  great  extent, 
the  prognosis  is  more  favorable  than  in  the  congenital  cases,  because  it 
has  been  demonstrated  that  if  the  operator  succeeds  in  replacing  the 
lost  parts  with  an  instrument  properly  constructed  and  suited  to  the  in- 
di\'idual  requirements,  normal  functions  will  be  restored  almost  imme- 
diately. The  patient  needs  but  to  accustom  himself  to  the  new  and 
strange  condition  in  w'hich  he  finds  himself,  to  be  able  to  speak  as  well 
as  ever  because  he  had  acquired  all  the  normal  habits  of  articulate 
speech  before  meeting  vrith.  disaster.  He  has  lost  part  of  the  natural 
organs  with  which  he  was  endowed,  but,  ha^^ng  known  their  uses,  he 
readily  accustoms  himself  to  the  artificial  substitute,  which  enables 
him  to  produce  the  same  sounds  by  the  same  movements  of  the  organs 
which  remain  intact.  As  the  instruments  to  be  made  for  persons 
suff erins;  from  such  misfortune  are  to  be  constructed  on  the  same  gen- 


788 


PA  LATA  L   M  ECHA  NISM. 


eral  principles  wliich  must  guide  tlie  dentist  in  the  treatment  of  congen- 
ital lesions,  description  at  this  point  is  unnecessary. 

Congenital  cleft  palate  is  a  division  of  the  roof  of  the  mouth  of  more 
or  less  extent,  which  is  present  in  the  infant  at  the  time  of  birth. 

Congenital  clefts  come  to  the  dentist  for  treatment  in  one  of  three 
conditions:  the  cleft  of  the  soft  palate  only,  \vhich  may  extend  to  the 
posterior  border  of  the  hard  palate  or  be  scarcely  more  than  the  di\'ision 
of  the  uyula,  as  in  Fig.  843;  the  cleft  of  the  soft  and  hard  palate,  in 
which  the  cleft  may  penetrate  the  bony  tissue  but  slightly  or  pass  through 
the  hard  palate  and  also  the  dental  process,  obliterating  entirely  the 
intermaxillary  bones,  as  in  Fig.  844:  any  of  the  above  conditions  com- 


FiG.  844 


plicated  in  an  endless  variety  of  ways  through  unsuccessful  surgical 
operations.  In  these  latter  cases  a  most  common  presentment  is  a 
bridging  of  the  gap,  with  the  soft  tissues  drawn  together  tensely,  leaving 
an  aperture  through  the  hard  palate  anteriorly  and  an  inadequate 
length  of  soft  ])alate  posteriorly,  the  tightly  drawn  tissues  which  form 
the  surgical  l)ridge  not  being  long  enough  to  occlude  with  the  posterior 
pharyngeal  wall;  or  where  there  has  been  only  a  cleft  in  the  soft  palate, 
the  cleft  is  usually  found  partially  closed,  with  no  advantage  to  the 
patient,  and  offering.a  greater  obstacle  to  the  success  of  the  dentist. 

In  some  of  these  cases  the  intervention  of  the  dentist  is  rendered 
useless,  while  in  those  where  it  is  possible  to  make  an  instrument,  the 
difficulty  of  constructing  the  same  is  greatly  increased,  owing  to  the 
complexities  of  the  altered  conditions. 


PALATAL   MKCHASISM.  789 

The  modern  instrument  which  the  skilled  dentist  supplies  to  a  cleft 
puliite  patient,  is  either  an  artificial  velum  or  an  obturator,  both  of  whieji 
are  admirably  adapted  to  the  correction  of  the  abnormal  speech  of  these 
sutferers,  and  either  of  which  may  be  retjuisite  in  a  special  case.  It  may 
be  stated,  however,  as  a  rule  for  guidance  in  general  practice,  that  the 
artijicial  cclum  will  more  tjifiekli/  enable  a  cleft-palate  patient  to  acquire 
the  art  of  speaking  correctly,  whilst  after  having  learned  to  speak  pro- 
perly the  obturator  may  aft'ord  him  equal  satisfaction. 

At  the  meeting  of  the  National  Dental  Association  in  1902  Dr.  Cal- 
vin S.  Case  presented  a  novel  form  of  artificial  palate  which  at  the  time 
he  denominated  an  artificial  velum  but  which  to  the  writer  appeared 
rather  to  operate  on  the  principal  involved  in  an  obturator,  although 
made  of  soft  rubber,  for  which  reason  he  would  term  it  a  soft  rubber 
obturator.  Since  then  Dr.  Case  has  called  his  instrument  a  velum- 
obturator,  this  double  term  apparently  depending  upon  the  fact  that  it 
is  so  fashioned  that  it  may  first  be  made  of  soft  rubber,  and  subse- 
quently the  same  molds  may  be  utilized,  for  the  making  of  a  dupli- 
cate in  hard  rubber.     The  device  will  be  described  later. 

The  knowledge  of  how  best  to  serve  a  cleft-palate  patient,  and  what 
manner  of  instrument  is  best  adapted  to  his  requirements,  necessitates 
an  intelligent  comprehension  of  his  needs,  as  well  as  of  the  principles 
upon  which  obturators  and  vela  are  constructed,  together  with  the 
uses  which  they  are  meant  to  serve. 

In  the  production  of  articulate  sounds  the  normal  individual  is  sup- 
plied with  a  soft  palate,  or  natural  velum,  of  great  mobility,  suspended 
from  the  posterior  border  of  the  hard  palate.  This  natural  velum 
serves  two  important  purposes.  First,  in  the  production  of  many  sounds 
it  is  necessary  to  prevent  the  nasal  resonance  which  would  result  if  the 
column  of  air  were  permitted  to  escape  through  the  nasal  passages. 
That  the  nasal  and  oral  cavities  may  be  completely  separated,  the  pos- 
terior wall  of  the  pharynx  rises,  forming  a  well-defined  ridge,  against 
which  the  velum  occludes,  being  drawn  backward  and  upward  to  meet 
it.  Thus  the  sound  is  forced  to  pass  exchisively  through  the  mouth, 
and  is  rendered  clear  and  distinct.  Second,  the  natural  soft  palate 
serves  as  an  abutment  against  which  the  tongue  rises  in  the  formation 
of  such  sounds  as  h,  g,  and  ng. 

A  cleft  of  the  palate  consequently  leaves  the  patient  with  no  means 
of  shutting  off  the  nasal  passages,  and  with  an  inadequate  organ  with 
which  to  produce  the  sounds  specified,  as  well  as  many  others. 

The  artificial  palate,  therefore,  whether  velum  or  obturator,  must 
enable  the  patient  to  completely  shut  off  the  nasal  passages,  and  it 
must  stop  the  gap  in  the  roof  of  the  mouth,  restoring  the  normal  vault, 
and  rendering  possible  the  production  of  all  the  sounds  with  which  the 
cleft  interfered.  The  artificial  velum  and  the  obturator  both  accom- 
plish this,  but  their  modes  of  action  are  quite  distinct. 

The  difference  between  an  obturator  and  a  velum  is  this — the  first 
recognizes  the  abnormal  condition  of  the  parts,  and  is  so  shaped  that, 
with  these  abnormal  parts  working  against  its  sides  and  end,  it  makes 


790 


PALATAL  MECHANISM. 


possible  the  proper  occlusion  of  the  iianvs  in  all  movements  of  the  j)alate, 
so  as  to  })roduce  perfect  speech,  the  obturator  itself  remaining  rigid, 
and  the  cleft  parts  sliding  against  the  lateral  sides,  these  being  so  shaped 
that  they  occlude  the  cavity  when  the  parts  are  at  rest,  and  therefore 
when  the  cavity  is  at  its  widest  opening,  and  they  are  so  slanted  that  as 
the  parts  are  drawn  together  and  brought  down  they  slide  along  the 
oblique  sides  of  the  obturator,  continuing  the  occlusion.     The  velum 


Fig.  84o 


Fig.  846 


is  a  mechanical  effort  to  reproduce  artificially  the  original  soft  palate 
which  is  missing.  It  is  a  flexible  bridge  across  the  chasm,  and  should 
as  nearly  as  possible  act  astlie  original  tissue  did.  Therefore,  Kingsley 
arranged  his  velum  so  that  when  it  rested  the  chasm  was  bridged. 
The  split  parts  of  the  artificial  velum  allowed  a  resting  place  for  the 
borders  of  the  cleft  soft  parts,  and  the  artificial  velum  was  made  suffi- 


Fii;.  St7 


ciently  flexible  so  that  in  any  position  they  might  assume  m  the  closing 
of  the  aperture,  they  would  carry  along  the  velum.  The  obturator  is 
rigid  and  immovable  and  the  soft  parts  move  against  it,  while  the  velum 
is  flexible  and  movable,  and  is  carried  with  every  movement  of  the  soft 
parts. 

The  artificial  velum  which  is  the  invention  of  Dr.  Norman  W,  Kings- 
ley,  is  made  of  soft  rubber  (vulcanite),  from  which  fact  it  is  clear  that 


PALATAL  MECHANISM. 


791 


the  theory  of  its  action  is  to  simulate  the  movement  of  the  natural 
organ  which  it  replaces.  Being  exceedingly  mobile,  it  responds  to  the 
movements  of  the  muscles  which  it  engages,  rising  and  falling  exactly 
as  a  natural  velum  would,  while  it  is  so  fashioned  that  at  the  same  time 
it  occludes  with  the  ridge  of  the  pharyngeal  wall,  completely  shutting 
off  the  upper  passages. 

The  Kingsley  velum  (Figs.  845-847)  consists  of  two  flaps  joined 
throughout  the  median  line.  The  lower  flap,  the  one  which  completes 
the  palatal  dome,  extends  from  the  apex  of  the  fissure  posteriorly  as  far 
as  the  bases  of  the  uvulae.  Its  general  form  is  that  of  a  triangle,  the 
apex  of  which  occludes  with  the  apex  of  the  cleft,  the  base  extending 
across  from  one  uvula  to  the  other.  This  flap  overlaps  the  soft  parts 
sufficiently  to  prevent  its  being  pushed  through  the  cleft  into  the  upper 

Fig.  848 


cavity.  The  other  flap  is  of  a  similar  triangular  shape,  the  posterior 
border,  however,  being  curved  and  thinned  out  to  a  feather  edge,  so 
that  when  in  occlusion  with  the  pharyngeal  wall  it  curls  up,  thus  pre- 
senting a  flat  surface  for  better  contact,  while  its  thinness  prevents 
irritation  to  these  sensitive  parts.  This  flap  is  above  the  fissure  and  rests 
upon  the  upper  surfaces  of  the  divided  palate.  The  two  flaps  are 
united  along  the  median  line,  so  that  when  complete  they  form  a  single 
appliance.  The  flaps  having  but  a  narrow  line  of  union,  grooves  are 
produced  laterally,  and  when  in  position  the  two  halves  of  the  soft 
palate  rest  in  these  grooves. 


792 


PA  LA  TA  L   MJX'IIA  XIS.U. 


In  connection  with  the  artificial  velum  a  metal  plate  is  constructed, 
clasped  to  the  teeth,  having  a  j)in  upon  tlie  upj)er  surface  wliich  passes 
through  a  hole  in  the  velum,  and  thus  holds  it  in  place  while  allowing 
it  lateral  motion.  Fig.  848  shows  an  instrument  in  position,  the  uvulae 
appearing  pentlant  below  the  grooves  of  the  artificial  palate.  Note  the 
relation  between  the  posterior  border  of  the  velum  and  the  wall  of  the 
pharynx.  The  rationale  of  this  appliance  is  as  follows:  in  the  effort 
to  close  off  the  upper  passage  the  sides  of  the  divided  natural  palate 


Fig.  810 


approximate  each  other,  and  at  the  same  time  are  drawn  upward. 
Thus  they  first  hug  the  artificial  velum  tightly,  and  then,  owing  to  its 
elasticity,  carry  it  upward.  Coincidently,  the  wall  of  the  pharynx 
rises,  forming  a  ridge  which  meets  the  feather  edge  of  the  artificial 
velum,  curling  it  up,  thus  accomplishing  perfect  contact,  completely 
preventing  the  escape  of  sounds  through  the  nasal  passages.  At  the 
same  time  the  velum,  completing  the  proper  arch  of  the  vault,  is  rigid 


Fig.  SoO 


enough  to  serve  as  an  efficient  abutment  for  the  tongue  when  necessity 
compels  such  contact.  Fig.  849  shows  the  upper  view  of  the  instru- 
ment seen  in  Fig.  848  and  is  introduced  to  give  a  clearer  idea  of  the 
attachment  of  the  velum  to  the  plate,  as  well  as  the  general  character 
of  the  grooves. 

As  stated  above,  the  flaps  which  constitute  the  velum  are  triangular 
in  shape,  yet  it  will  be  observed  that  the  velum  shown  in  Fig.  848  is 


PALATAL   Mi:clfA.\fS}[. 


703 


square  at  ilu"  anterior  cml.  \\'liere  the  cleft  is  in  the  soft  palate  only 
tiie  trianifular  vehnn  is  i-ecjuired,  hut  where  the  cleft  passes  forward, 
entering  the  hard  palate,  it  is  frequently  more  desirable  to  fill  the  aper- 
ture in  the  hard  palate  by  vulcanizing  hard  rubber  upon  the  upper  side 
of  the  metal  plate,  the  soft  rubber  velum  having  a  square  end  to  meet 
a  similar  surface  of  the  hard  rubber. 

Such  an  instrtiment  is  seen  in  Fig.  850,  the  abutment  of  the  hard 
and  soft  rubber  being  clearly  indicated.  The  projecting  point  seen  in 
this  figure  was  for  a  special  purpose,  and  is  not  ordinarily  required. 
This  patient  was  a  girl  aged  fourteen,  and  presented  an  extensive  fis- 
sure through  hard  and  soft  palate,  complicated  with  a  hare-lip,  upon 
which  a  fairly  good  result  had  been  obtained  by  a  surgical  operation  in 


Fig.  851 


early  life.  Fig.  Sol  shows  a  model  of  her  mouth,  the  aperture  seen 
above  the  incisors  representing  the  passage  of  the  fissure  through  to  the 
nose,  but  somewhat  exaggerated,  having  been  enlarged  with  a  knife  for 
convenience  in  constructing  the  instrument.  The  girl's  articulation 
was  bad,  but  the  g-reatest  difficult v  of  understanding  her  arose  from  the 
excessive  nasal  quality  of  her  voice.  Externally,  she  was  much  dis- 
figured by  the  fact  that  the  ala  of  the  nose,  on  the  side  where  the  hare- 
lip had  been,  was  more  sunken  than  is  usual — so  much  so,  indeed, 
that  the  nostril  on  that  side  was  completely  closed.  If  the  reader  will 
read  aloud  a  few  lines  on  this  page,  and  while  doing  so  will  close  one 
nostril  by  pressing  down  the  ala  with  one  finger,  he  will  readily  discover 
that  such  closure  of  the  nostril  produces  considerable  nasal  quality  of 


794  PALATAL  MECHANISM. 

voice.     Thus  it  was  very  desirable,  both  from  a  cosmetic  standpoint 
and  for  the  benefit  of  her  speech,  that  the  sunken  ahi  shouhl  l)e  raised. 
Indeed,    the    father  of  the  child  earnestly  solicited  an  attempt  of  this 
nature.  Thereupon  the  writer  adopted  what  proved  to  be  a  simple  and 
effectual  method  of  accomplishing  the  desired  end.     The  metal  plate 
having  been  fitted,  a  scjuare  platinum  bar  was  soldered  to  the  upper 
side  and  bent  so  that  it  protruded  through  the  nostril,  when  it  was  cut 
off  short  enough  to  be  out  of  sight.     The  hard  rubber  intended  to  plug 
the  aperture  in  the  hard  palate  was  then  attached, and  with  the  soft- 
rubber  velum  in  position  the  result  is  seen  in  Fig.  850,  the  end  of  the 
platinum  bar  being  shown  at  a.     The  next  step  was  to  make  a  square 
tube  which  should  telescope  over  the  platinum  l)ar,  fitting  accurately, 
so  that  motion  would  be  prevented.     To  the  end  of  this  tube  was  sol- 
dered a  platinum  button,  so  placed  that  when  in  position  it  rested  against 
the  inner  surface  of  the  sunken  ala  and  liftecl  it  to  a  proper  position. 
Two  \'iews  of  this  tube  and  button  attachment  are  shown  in  Fig.  850. 
In  use  the  instrument  is  placed  in  the  mouth,  the  platinum  bar  passing 
readily  into  the  nostrils;  then  the  button  attachment  is  slipped  over  the 
bar  through  the  external  orifice  of  the  nose,  the  ala  being  thus  disten- 
ded, and  at  the  same  time  exerting  sufficient  pressure  to  prevent  its 
dislodgement.     The  fixture  is  worn  with  comfort,  and  the  button  at- 
tachment is  tolerated  by  the  nose,  the  pressure  not  being  sufficient  to 
produce  ulceration  or  absorption.      ■Moreover,  while  the  child's  speech, 
of   course,   was   not   immediately    improved    by    the   introduction   of 
the  palate  instrument,  the   nasal  resonance  was  very   markedly  les- 
sened instantly  by  the  lifting  of  the  ala.     Consequently,  it  was  but   a 
question  of  time  when  her  speech  was  rendered  normal,  which  it  never 
would  have  been  with  one  nostril  closed. 

It  may  be  well  to  emphasize  the  fact  that  the  mere  insertion  of  an 
artificial  palate  cannot  be  expected  to  enable  the  patient  to  speak  cor- 
rectly, any  more  than  the  possession  of  a  piano  or  \nolin  would  make 
the  owner  an  accomplished  musician.  The  artificial  palate,  properly 
constructed,  supplies  the  patient  with  the  means  of  perfecting  his 
speech,  but  perfection  itself  must  come  through  practice.  Education 
by  a  teacher  who  thoroughly  comprehends  the  needs  of  the  cleft-palate 
patient  will  greatly  shorten  the  time  required  for  improvement,  as  well 
as  insure  a  better  final  result.  But  the  co-operation  of  the  patient  is  a 
retpiisite  which  is,  strangely  enough,  not  always  to  be  counted  upon. 
And  it  is  those  persons  who  have  no  ambition  to  help  themselves,  who 
have  claimed  that  artificial  palates  have  done  nothing  for  them.  An 
instance  of  this  was  noted  in  a  young  man  at  college  and  approaching 
manhood  who  seemed  to  have  no  conception  of  the  wretched  sound  of 
his  speech.  An  instrument  admirably  adapted  to  his  needs,  and  one 
which  undoubtedly  made  it  possil)le  for  him  to  attain  perfect  speech, 
was  worn  by  him  but  three  months,  and  then  discarded  as  of  no  value 
to  him. 

One  reason  why  the  artificial  palate  cannot  be  expected  to  enable 
the  patient  to  speak  properly  at  once  is  this:   with  normal  organs  one 


PALATAL  MECHANISM. 


7dl 


produces  articulate  sounds  by  utilizing  the  normal  actions  of  his  throat- 
muscles  and  the  tongue  and  lips.  With  abnormal  organs,  as  with  a 
cleft  palate  and  hare-lip,  the  individual,  in  the  efi'ort  to  produce  the 
sounds  which  he  hears  from  others,  compels  his  tongue,  lips,  and  throat- 
muscles  to  adopt  habits  which  are  totally  dissimilar  to  normal  move- 
ments. When,  therefore,  the  artificial  palate  is  inserted,  with  which 
perfect  speech  can  be  attained  only  by  normal  movements,  it  is  evi- 
dent that  the  incorrect  habits  must  first  be  overcome;  and,  secondly, 
the  correct  action  of  the  organs  must  be  acquired.  Consequently, 
those  dentists  who  report  that  instruments  of  their  devising  correct 
the  patients'  defective  speech  instantly,  simply  report  what  is  not,  and 
cannot  be  true  if  the  case  be  of  congenital  origin. 

Since  the  acquirement  of  wrong  modes  of  speech  must  prove  so  de- 
terring to  the  patient  who  essays  to  improve  his  speech  by  resorting  to 

Fig.   852 


an  artificial  palate,  it  is  a  reasonable  corollary  that  the  earlier  the  in- 
strument is  made  the  less  will  the  patient  have  to  overcome.  It  is, 
therefore,  both  wise  and  feasible  to  insert  appliances  even  before  the 
appearance  of  the  permanent  teeth.  The  co-operation  of  the  patient, 
however,  being  of  such  importance,  especially  where  lessons  in  articu- 
ation  are  to  be  given — which  is  always  desirable — it  is  scarcely  wise  to 
undertake  a  case  until  the  little  patient  is  old  enough  to  appreciate  the 
conditions  and  their  remedy.  Therefore,  except  in  rare  cases  where 
the  child  is  unusually  well  developed  and  mentally  bright,  it  is  best  to 
wait  until  the  fifth  or  sixth  year. 

This  statement  is  introduced  at  this  point  because,  whatever  doubt 
there  may  be  in  older  patients  as  to  the  choice  between  the  soft  velum 
and  the  obturator,  with  children,  and  especially  young  children,  the 
velum,  is  the  one  and  only  best  dependence. 


796  PA  LA  TA  L   Ml'X  'HA  NISM. 

An  obturator  is  an  instniiiKMit  (l('.si;2;n(Ml  to  merely  fill  a  <i;ap  or  dose 
an  oj)eiiiiiy'  in  the  palate.  To  he  of  any  .servic*e  the  instrnnieiit  must  be 
so  construeted  that  it  accomplishes  all  that  the  artificial  velum  enables 
the  patient  to  do,  even  though  in  an  entirely  ditt'erent  manner.  It 
must  accurately  fill  the  cleft  when  the  parts  are  at  rest;  //  mu.st  also 
fill  the-  fissure  ivhencvrr  and  no  maftrr  how  far  fhe  movable  .sides-  of  the 
cleft  are  drawn  npward.  To  serve  such  a  ])urpose  the  obturator  must 
be  so  thick  that  when  the  sides  of  the  palate  are  drawn  uj)ward  to  their 
greatest  limit  th(>y  still  rest  against  the  sides  of  the  obturator.  More- 
over, it  must  be  of  sufficient  length  to  be  reached  by  the  posterior  wall 
of  the  pharynx,  and  it  must  be  thick  enough  at  the  back  end,  so  that 
when  the  pharynx  does  come  into  contact  with  it  the  closure  of  the  pos- 
terior nares  will  be  complete.  When  using  the  term  "thick,"  allusion 
is  made  to  the  diameter  through  the  obturator  from  the  oral  to  the 
nasal  surface,  not  to  the  thickness  of  the  rubber,  for  these  obturators 
are  hollow  bulbs,  and  the  rubber  has  liut  the  thickness  of  a  single  sheet. 

In  Fig.  852  is  shown  a  model  with  an  ol)turator  in  position.  The 
plate  is  made  of  iridio-platinum  and  the  obturator  is  a  hollow  bull)  of 


hard  rubber.  This  figure  shows  the  length  of  the  obturator  in  relation 
to  the  uvuliTe,  as  well  as  the  manner  in  which  the  oral  surface  of  the 
instrument  fills  the  gap  and  completes  the  arch  of  the  vault.  In  Fig. 
853  the  same  instrument  is  shown  in  profile.  It  is  seen  that  the  rubber 
bulb  is  attached  to  the  metal  plate  by  passing  over  a  bar  wdiich  is  sol- 
dered to  the  plate,a  nut  holchng  it  fast.  Thus  the  bulb  may  be  removed 
in  order  to  repair  or  alter  clasps  or  to  do  anything  recpiiring  the  oper- 
ation of  soldering,  which  should  be  difficult  to  properly  perform  were 
the  rubber  bulb  permanently  attached.  The  figure  also  shows  the 
thickness  of  the  obturator,  which  is  so  shaped  that  as  the  divided  pal- 
ate rises  contact  is  preserved.  This  instrument  is  a  modification  of  the 
original  Suersen  device. 

In  use,  an  obturator  of  this  kind,  unlike  the  artificial  velum,  is  sta- 
tionary in  its  position,  but  it  is  of  such  form  that  the  pharyngeal  muscles 
of  the  throat  in  the  movements  incidental  to  the  production  of  articu- 
late sounds  hug  the  obturator,  and  so  separate  the  cavity  of  the  nose 
from  the  cavity  of  the  mouth. 

In  the  American  System  of  Dentistry  (vol.  ii.  p.  lOGS)  there  is  figured 
a  Suersen  obturator,  modified  by  the  addition  of  a  hinge,  for  which  the 
following  claim  is  made:  "The  main  advantages  of  this  appliance  are — 
that  it  is  made  of  a  durable  material,  is  easilv  constructed,  and  that 


PA  LA  TA  L    M fa: II A  XIS.M. 


797 


arficulation  can  he  learned  with  it  more  readilij  than  with  anij  other  ap- 
pliance." This  claim  appears  to  be  based  upon  the  operation  of  the 
hinge  which  unites  the  obturator  with  the  plate,  but  this  is  a  misleading 
device.  To  the  inexperienced  it  might  appear  to  be  an  improvement, 
but  in  actual  practice  it  will  l)e  found  to  possess  no  advantage  over  the 
Suersen  obturator  without  the  hinge. 

Fig.     854 


That  the  reader  may  better  comprehend  the  explanation  of  this  fact, 
illustrations  of  a  hinged  obturator  have  been  introduced.  Fig.  854 
gives  a  ^^ew  from  the  oral  aspect,  while  Fig.  855  shows  the  upper  side. 
In  both  figures  A  represents  the  metal  plate,  B  the  hinge,  and  C  the 
rubber  bulb  or  obturator. 

Unlike  the  artificial  velum,  the  obturator  may  be  immovable  and  yet 


Fig.  So, 


serve  its  purpose,  because  the  soft  parts  throughout  all  their  varied 
motions  are  always  in  contact  ^^th  the  instrument,  the  utterance  of 
articulate  sounds  being  thus  rendered  possible.  The  addition  of  the 
hinge  is  intended  to  allow  the  liftino-  of  the  obturator.  Even  grantino; 
that  the  levator  muscles  would  he  powerful  enough  to  accomplish  this 
the  question  arises.  What  will  be  gained?     Unfortunately,  nothing. 


798  FALATir   MECHANISM. 

because  the  same  benefits  will  obtain  with  an  instrinnciit  of  exactly  the 
same  shape,  immovably  attached.  But  when  further  examination  of 
this  sort  of  appliance  is  made  in  the  mouth,  it  is  readily  seen  that  the 
levator  muscles  do  not  lift  the  hinged  obturator,  but,  on  the  contrari/,  they 
raise  the  sides  of  the  cleft,  ivhich  slide  along  the  bulb  exactly  as  though  it 
were  immovable. 

The  original  of  the  instrument  shown  in  Figs. 854  and  855  was  made 
for  a  patient  who  for  years  had  been  wearing  a  soft-rubber  velum,  with 
which  he  had  learned  to  speak  correctly.  This  hinged  obturator  did 
not  rise  and  fall  as  it  was  expected  to  do,  and  the  patient  discarded  it 
and  reverted  to  the  velum.  Nevertheless,  with  the  hinged  instrument 
this  patient  talked  very  well,  the  reason  being  that,  having  learned  to 
speak  with  his  velum,  he  could  speak  with  the  obturator,  and  this  in 
spite  of  ihe  failure  of  the  hinge  action. 

One  of  these  appliances  was  made  for  a  young  lady  who  was  assured 
that  she  would  speak  well  within  a  year,  but  at  the  end  of  three  years 
no  improvement  was  noticed.  An  examination  of  the  appliance  in  the 
mouth  showed  that  the  levator  muscles  did  not  lift  the  bulb  at  all,  and 
it  was  more  of  an  embarrassment  than  an  advantage.  Unlike  the  pre- 
vious case,  where  the  patient  had  learned  to  speak  with  a  soft  velum, 
this  hinged  instrument  was  the  inital  effort  made  for  her  relief.  Again 
the  hinge  failed,  and  the  obturator  was  practically  the  same  as  one  con- 
structed without  a  hinge.  But  this  patient  found  her  appliance  of  no 
benefit  to  her,  whereas  when  she  was  given  the  same  plate  with  the  same 
hinge,  but  with  a  soft-rubber  velum  attached  to  it,  a  course  of  instruction 
covering  a  few  weeks  enabled  her  to  speak  quite  well,  and  she  will  un- 
questionably continue  to  improve  until  her  speech  is  perfect. 

These  two  cases  emphasize  the  fact,  which  should  be  prominently 
borne  in  mind,  that  the  soft-rubber  velum  is  the  instrument  best 
adapted  for  correcting  the  speech  of  cleft-palate  patients;  that  having 
learned  to  speak  by  using  a  soft-rubber  velum,  these  persons  will  do 
well  with  a  Suersen  obturator,  with  a  hinged  obturator  whether  the 
hinge  works  or  not,  and  in  some  cases  even  with  the  crude  class  of  in- 
struments designed  for  no  other  purpose  than  to  stop  the  opening  in  the 
hard  palate. 

There  is  but  one  possible  condition  where  a  hinge  is  needed  in  con- 
nection with  a  hard-rubber  bulb,  and  that  is  where  a  surgical  operation 
has  failed,  a  bridge  having  been  constructed  across  the  centre  of  the 
fissure,  leaving  a  cleft  posteriorly  and  a  perforation  anteriorly.  The 
instrument  for  which  a  case  may  be  a  hard-rubber  l)ull)  which  passes 
through  the  anterior  opening,  filling  the  posterior  cleft  and  reaching  to 
the  pharyngeal  w^all  during  the  act  of  speaking.  Such  a  bulb  is  hinged 
to  the  plate,  and  it  necessarily  rises  and  falls,  because  it  rests  upon  the 
upper  side  of  the  surgical  bridge,  and  the  levator  muscles  cannot  elevate 
the  halves  of  the  divided  palate  without  raising  this  bridge  and  with  it 
the  extension  which  carries  the  obturator.  It  is  rare  that  such  an  ante- 
rior opening  will  permit  the  passage  of  the  hard  bulb,  though  such 
cases  have  been  treated.     It  would  be  preferable  however  to  sever  the 


PALATAL  MECHANISM.  799 

surgical  bridge,  allowing  the  cleft  to  reassume  its  original  condition, 
than  to  resort  to  so  complicated  a  device. 

The  history  of  an  instructive  case  which  passed  through  the  writer's 
hands  is  here  given.  Before  describing  this  case  reference  must  be 
made  to  another  sort  of  obturator  which  had  been  employed  in  this 
instance.  The  object  in  hinging  a  hard-rubber  obturator  is  to  furnish 
an  instrument  which  will  simulate  the  action  of  the  artificial  velum. 
In  Germany  the  same  result  had  been  sought  in  a  different  manner. 
I  do  not  know  who  claims  to  be  the  inventor  of  the  method,  but  the  one 
which  was  seen  in  this  case  was  made  by  Dr.  C.  Schultsky  of  Berlin. 
This  was  merely  a  soft-rubber  obturator — in  other  words,  a  soft-rubber 
bulb — hollow  like  the  hard-rubber  bulbs,  but  so  fashioned  that  it  could 
be  inflated  something  after  the  manner  of  the  pneumatic  bicycle  tire. 
The  idea  evidently  is  that  the  soft-rubber  ball,  placed  in  the  back  of 
the  throat,  may  be  compressed  by  the  muscles,  thus  serving  to  fill  the 
gap  under  all  circumstances.  The  history  of  the  patient  is  as  follows: 
Mr.  F was  born  in  Posen,  Germany,  in  1861,  and  was  thirty- 
four  years  of  age  when  he  presented  himself  for  treatment.  At  birth 
he  had  a  fissure  of  the  soft  palate  which  reached  forward  to  the  border 
of  the  hard  palate,  but  did  not  extend  into  the  bone.  Nevertheless,  he 
had  a  hare-lip,  which  was  operated  upon  during  infancy  with  but  par- 
tial success,  an  opening  being  left  near  the  nostril.  At  thirteen  Dr. 
Suersen  made  for  him  an  obturator  having  a  hard-rubber  bulb.  This 
was  worn  for  a  year,  when  the  clasp  on  one  side  was  broken  and  the 
fixture  was  abandoned.  At  the  age  of  twenty  Prof.  Wolf  of  Berlin  ac- 
cepted him  as  a  patient  at  his  private  clinic  and  undertook  to  close  the 
cleft  surgically,  and  at  the  same  time  performed  a  supplementary  oper- 
ation on  the  lip.     This  latter  operation  was  a  complete  success,  and  Mr. 

F has  now  a  good  lip  both  in  appearance  and  usefulness.     A  heavy 

moustache  almost  completely  covers  the  scar,  so  that  there  is  no  exter- 
nal evidence  of  his  deformity.  The  operation  upon  the  cleft,  however, 
was  another  addition  to  the  list  of  cases  where  the  failure  of  surgical 
measures  has  rendered  the  dentist's  work  more  complicated,  without 
compensating  advantage  to  the  patient.  The  cleft  originally  extended 
to  the  border  of  the  hard  palate,  so  that  it  would  have  been  compara- 
tively simple  to  provide  for  him  an  artificial  velum  similar  to  that 
shown  in  Figs.  848  and  849.  After  learning  to  speak  he  could  then  have 
had  an  obturator  should  he  have  desired  it.  The  operation,  however, 
by  partly  closing  the  cleft  constructed  a  bridge  of  soft  tissue  over  which 
a  plate  could  not  be  worn,  so  that  it  became  necessary  to  have  an  ex- 
tension to  the  plate  which  should  carry  the  appliance  used  to  fill  the 
gap.  Thus  the  patient  was  very  much  worse  off  after,  than  before  his 
operation.  A  year  later  he  placed  himself  under  the  care  of  a  dentist. 
Dr.  C.  Schultsky  of  Berlin,  who  made  for  him  a  soft-rubber  obturator. 
All  that  remains  of  this  instrument  is  shown  in  Fig.  856.  This  consists 
of  a  vulcanite  plate  clasped  to  the  natural  teeth  and  carrying  a  few 
artificial  teeth.  Immediately  at  the  posterior  border  is  a  small  extension 
(a),  also  of  vulcanite,  which  is  connected  with  the  plate  proper  by  a 


800 


/ '.  1  LA  T.  I  /.   Mh'(  'HA  MSM. 


gold  slide  ih)  which  moves  forward  and  backward  in  a  inctal  slot,  thus 
providinij;  for  antero-posterior  movement.  Next  there  is  a  gold  spiral 
spring  (c),  which  permits  the  obturator  to  follow  the  play  of  the  mus- 
cles in  any  direction.  At  the  posterior  end  of  the  gold  spring  was  per- 
manently fastened  a  soft -rubber  bulb  or  ball  id).  Judging  from  what 
was  left  of  this  bulb,  it  may  be  inferred  that  originally  it  was  (|uite  thick 
along  that  portion  which  formed  the  palatal  surface  and  was  intended 
to  complete  the  arch  of  the  vault.  Into  this  thick  portion  the  spring 
was  fastened.  Thinner  walls  extended  upward,  completing  the  bulb 
and  leaving  it  hollow.     Tliere  was  some  sort  of  orifice  and  stop-valve, 


Fig.  8.50 


inadecjuately  described  by  the  patient,  through  which  he  was  instructed 
to  inflate  the  bulb  every  morning,  the  air  gra(hially  escaping  during 
the  day. 

He  wore  this  instrument  for  five  years;  during  this  time,  however, 
the  bulb  burst,  whereupon  he  continued  to  wear  it  in  its  ruptured  con- 
(Htion.  Then  he  had  a  second  bulb  attached  by  the  same  dentist, 
which  after  a  brief  time  also  burst.  Nevertheless,  he  continued  to  use 
this  appliance  for  eight  years  more,  and  the  figure  shows  the  fixture  as 
I  found  it.  Two  facts  in  connection  with  this  case  are  peculiarly  in- 
structive: so  long  as  the  orig-inal  bulb  remained  whole  there  was  no 
improvement  in  the  patient's  speech;  second,  after  it  had  burst  he  no- 
ticed a  very  rapid  change,  and  within  two  years  he  was  speaking  with 
approximate  correctness.     Thus  the  ruptured  bulb  was  better  than  the 


PA  LA  TA  L  MECHANISM. 


801 


soft-rubber  obturator  which  it  was  intended  to  be;  and  the  point  of 
j2;reat  interest  here  is  that,  though  in  a  very  crude  way,  still  in  principle, 
the  bulb  became  a  Kinc/slei/  .soft  velum  as  soon  as  it  was  ruptured.  This 
can  be  better  comprehended  by  comparing  Fig.  SolJ  (Dr.  Schultsky's 
instrument  with  bulb  ruptured)  with  Fig.  857  (which  shows  the  appli- 


FiG.  857 


ance  constructed  for  him  by  the  writer).  It  w41l  be  seen  at  a  glance 
that  the  velum  here  appears  to  differ  from  the  typical  form  shown  in 
Figs.  845-847  in  the  fact  that  there  is  but  a  single  flap.  It  is  there- 
fore necessary  to  explain  how  it  is  that  the  principle  is  the  same  though 
the  form  is  different.     The  typical  velum  has  two  flaps,  one  of  v^"hich 


Fig.  S58 


lies  in  the  upper  cavity  resting  upon  the  sides  of  the  cleft,  wiiile  the 
lower  flap  is  below,  the  two  forming  grooves  in  which  the  sides  af  the 
cleft  move.  When  closed,  the  uvulpe,  or  extreme  posterior  ends  of  the 
split  velum,  approximate  one  another,  hugging  the  artificial  velum 
closely. 

Fig.  858  shows  a  model  of  a  mouth,  and  the  absence  of  the  u^•ul8e 


51 


802 


PALATAL  MECHANISM. 


will  be  observed.  The  uvul«;  were  originally  present,  but  were  destroyed 
by  the  surgical  operation,  and  the  sides  of  the  cleft  posteriorly  are 
now  continuous  with  the  pillars  of  the  fauces.  Here,  therefore,  there 
was  no  need  for  grooves,  there  being  no  possibility  of  the  close  ap- 
proach of  the  sides  of  the  cleft.  A  single  flap  was  made,  such  as  is 
shown  in  Fig.  857.  The  anterior  edges  were  made  heavier  than  usual, 
to  offer  sufficient  resistance  to  ensure  the  raising  of  the  hinge  extension 
which  connected  the  velum  with  the  plate  in  the  roof  of  the  mouth. 
The  single  flap  is  similar  in  the  theory  of  its  office  to  the  single  flap  of 
Dr.  Sereombe,  but  modified  to  assume  the  more  practical  form  seen  in 
the  upper  flap  of  the  Kingsley  velum.     Dr.  Sereombe  claimed  that  the 

Fig.   859 


flap  should  not  reach  the  posterior  wall  of  the  pharynx;  in  this  he  made 
a  grave  error. 

Here,  then,  may  be  indicated  the  reason  why  the  hinge  is  of  no  value 
with  an  obturator,  and  yet  becomes  a  necessity  with  such  a  case  as  the 
last  two — viz.  where  the  apex  of  the  fissure  is  distant  from  the  posterior 
border  of  the  hard  palate.  Obturators  are  constructed  of  hard  rubber, 
have  sloping  sides,  and  are  highly  polished.  In  the  efforts  to  close  the 
cavity  of  the  nares  the  levator  muscles  draw  the  sides  of  the  cleft  up- 
ward and  slightly  backward,  and  if  a  patient  can  be  made  to  swallow 
with  the  mouth  open,  the  operator  will  readily  discover  that  the  tissues 
slide  along  the  smooth  sides  of  the  obturator,  but  do  not  raise  it.  The 
hinge,  therefore,  is  useless.  With  the  other  condition  a  totally  differ- 
ent result  obtains.  The  soft  velum,  lying  entirely  upon  the  upper  sur- 
face of  the  cleft,  and  the  anterior  edge  of  the  velum  being  stiff  and  v/ide, 
while  the  apex  of  the  fissure  presents  the  usual  angle,  it  follows  that  the 


PALATAL  MECHANISM.  803 

natural  palate  cannot  rise  without  carrying  the  superincumbent  velum 
with  it.  This  it  could  not  accomplish  if  the  extension  which  connects 
the  velum  with  the  plate  were  unyielding.  Consequently,  the  hinge  is 
a  positive  necessity.  Fig.  859  is  the  same  as  Fig.  858  with  appliance 
in  position,  tlie  dotted  line  indicating  the  border  of  the  velum,  which  is 
above  the  fissured  sides  of  the  palate,  and  making  it  clear  that  no  move- 
ment can  displace  it,  while  the  least  retraction  of  the  tissues  must  be 
followed  by  a  responsive  movement  of  the  velum  and  the  hinged  ex- 
tension. In  the  figure  the  velum  is  seen  at  A  and  the  hinge  at  B.  The 
plate  in  this  instance  was  made  of  vulcanite  to  suit  the  wishes  of  the 
patient,  his  original  plate  having  been  of  that  material.  Metal  would 
have  been  preferable. 

Fig.  860  is  of  special  interest:  it  shows  a  similar  instrument  having 
a  hinged  extension,  but  the  soft  velum  is  of  the  typical  form,  because, 
although  there  was  a  great  space  between  the  border  of  the  hard  palate 
and  the  apex  of  the  fissure,  thus  necessitating  the  hinged  extension, 
nevertheless  the  fissure  itself  was  fairly  regular,  the  uvulae  being  pres- 

FiG.  860 


ent,  and  the  two  sides  of  the  cleft  when  shutting  off  the  cavity  of  the 
nares  working  co-ordinately.  The  model  of  this  case  is  seen  in  Fig. 
863,  while  the  instrument  with  tiny  velum  is  shown  in  Fig.  860.  In 
connection  with  hinged  artificial  palates  it  is  also  of  interest  to  record 
the  fact  that  this  case  was  treated  by  Dr.  Kingsley  some  thirty-five 
years  ago. 

I  have  elsewhere  stated  that  it  is  but  rarely  advisable  to  attempt 
mechanical  assistance  earlier  than  the  fifth  or  sixth  year.  Indeed  at 
the  time  when  that  statement  was  written  I  had  known  of  but  two  in- 
struments made  for  very  young  children.  One  was  in  the  case  of  a 
girl  of  six.  Surgical  interference  had  left  a  slight  aperture  along  the 
median  line,  anteriorly,  while  the  union  of  the  soft  parts  promised  to 
be  adequately  satisfactory.  For  this  patient  Dr.  Kingsley  made  a  tiny 
carrying  plate  to  cross  and  cover  the  forward  aperture,  which  was  com- 
pletely occluded  with  a  hard  rubber  attachment  on  the  upper  side  of 
the  carrying  plate. 

The  idea  was,  that  by  closing  this  orifice,  and  with  proper  training 
the  child's  speech  might  improve,  and  this  anticipation  proved  well 
founded.     It  is  of  interest  to  record,  however,  that  later  a  retrogression 


804 


PA  LA  TA  L  MECHA  NISM. 


occurred  and  then,  some  years  after  it  was  seen  that  witli  lierfrrowtli 
the  child  actually  developed  a  cleft  palate.  The  sides  of  the  united 
palate  grew,  while  the  cicatricial  tissue  along  the  line  of  union  acted  as 
a  barrier  to  development  in  that  region,  the  result  being  that  at  twelve 
years  of  age  a  well  defined  cleft  was  present,  and  Dr.  Kingsley  was 
compelled  to  insert  a  regular  instrument  carrying  a  soft  velum. 

In  another  case  he  made  a  soft  velum  instrument  for  a  girl  of  seven  or 
eight,  but  it  has  been  my  pleasure  to  have  pass  through  my  hands  an 
interesting  little  subject  aged  only  four  for  whom  a  velum  instrument 
has  been  successfully,  and  I  think  advantageously  supplied.  By  this 
I  mean  that  the  result  already  seems  to  prove  that  it  was  better  to  supply 
the  instrument  early,  rather  than  to  wait,  and  this  in  spite  of  the  fact 
that  the  child  has  had  no  instruction  except  such  as  could  he  given  by 


Fig. 861 


its  mother.  Yet  now,  at  the  age  of  five  she  attends  a  kindergarten  and 
can  make  herself  understood  by  her  playmates,  whose  comptmionship 
before  she  had  shunned. 

This  child  was  sent  to  me  by  a  surgeon  who  had  already  twice  oper- 
ated unsuccessfully.  Indeed  the  attempts  but  left  the  mouth  in  a  worse 
condition.  The  illustration  (Fig.  861)  shows  the  original  cleft  partly 
closed,  but  an  ugly  mass  of  scar  tissue  now  occupies  the  forward 
part  of  the  original  cleft,  and  the  edges  are  so  thick  that,  thougli  what 
may  be  called  a  Kingsley  velum  was  made  for  the  case,  its  appearance 
is  quite  unlike  the  usual  form  (Fig.  862  ). 

Allusion  has  been  made  to  a  new  artificial  palate,  or  velum  obturator, 
the  invention  of  Dr.  Calvin  S.  Case.  The  following  is  Dr.  Case's  des- 
cription of  his  instrument. 

"llirough  a  desire  to  take  advantage  of  the  benefits  afforded  by  a  soft- 


P.I  LA  TA  L   MKCIIA  SISM. 


80o 


rubber  appliance  on  tlie  one  liand,  ami  a  hard-rubber  obturator  on  the 
other,  and  at  the  sanic^  time  avoid  the  possibihties  of  the  hnal  inefficiency 
of  the  one  and  the  cHfticuhies  in  construction  and  adjustment  presented 
by  the  other,  has  risen  the  present  artifiical  palate,  which  it  is  the  object 
of  this  paper  to  present. 

It  essentially  consists  of  a  form  of  palate  which  can  first  be  made  of 
soft  rul)l)er  and  possess  all  the  advantages  of  the  Kingslev  velmn,  and 
then  when  the  patient  has  become  accustomed  to  it  in  its  flexible  state, 
and  its  form  is  an  assured  success  })y  packing  the  same  casts  in  which 
the  s(-)ft  rubber  palates  were  vulcanized  with  another  quality  of  rubber, 
a  hard-rubber  palate  is  produced  which  possesses  all  the  advantages  of 
a  perfect  obturator. 

If  made  of  softer  rubber  the  first  palate  can  be  worn  without  irritation 
or  special  inconvenience  ;  after  which,  desired  changes  in  its  form,  that 


Fig.  S62 


v^ 


are  nearly  always  recjuired  to  perfect  the  palate,  can  then  be  easily 
made  bv  sKghtlv  enlarg-ino-  or  contractino-  the  metal  mold  in  which  it  is 
vulcanized. 

Those  who  are  familiar  ^^•ith  the  Kingsley  palates,  which  I  am  pleased 
to  say  I  have  used  with  great  satisfaction  in  my  practice  for  over  twenty 
years,  will  remember  that  the  veil  or  posterior  portion  of  the  palate  is 
sustained  by  extending  the  central  thickened  portion  into  it,  and  from 
this  point  it  is  gradually  flattened  to  a  comparatively  th.in  edge,  where 
it  is  more  or  less  curved  in  conformity  to  pharyngeal  wall,  against  which 
it  is  intended  to  rest  during  the  contracion  of  the  pharyngeal  and  the 
palatal  muscles. 

In  this  particular  it  is  C[uite  different  in  form  from  the  palate  I  am 
about  to  describe,  in  that  with  the  latter  all  the  central  portion  of  the 
palate  is  thin,  while  the  edge  of  the  veil  is  thick,  in  the  form   of   a 


806  PALATAL  MECHANISM. 

solid  roll  about  one-fifth  of  an  inch  in  diameter,  or  preferably  trianfjular, 
with  rounded  corners,  so  that  its  outer  flattened  surfaces  exactly-  and 
firmly  fit  the  pharynt^eal  walls  when  the  jnuscIcs  arc  in  <i  coniractcd  date. 

Fig.  803  represents  the  palatal  view  of  the  artificial  j)alate,  with  trans- 
verse section.  Fig.  8()4  shows  transverse  sections  through  the  mesial 
plane.     Figs.  865  and  806  show  the  palate  in  position. 

In  extensive  clefts  the  borders  of  the  veil  extend  forward  along  the 
lateral  walls  of  the  pharynx  and  posterior  nares,  anfl,  becoming  thinner, 
form  the  borders  of  the  nasal  extensions  which  rest  upon  the  floor  of 
the  nares. 

Fig.  863 


When  the  cleft  does  not  extend  into  the  hard  palate,  the  veil  is 
shaped  in  a  similar  manner,  but  with  the  nasal  portion  abridged  to 
meet  the  requirements  of  the  case. 

Where  the  cleft  extends  into  the  hard  parts,  the  body  of  the  palate 
which  covers  the  borders  of  the  cleft  and  forms  the  lateral  wings  on 
the  roof  of  tlie*  mouth  should  not  extend  back  of  the  attachments  of 
the  bifurcated  velum  palati,  nor  in  any  way  interfere  with  the  free 
action  of  the  muscles  ;  neither  should  it  extend  upon  the  roof  of  the 
mouth  any  farther  than  is  necessary  to  give  a  firm  seating  for  the 
palate.  This  portion  should  be  about  as  thick  as  an  ordinary  rubber 
plate,  being  thinned  along  its  oral  borders  and  thickened  to  form  the 
nasal  borders. 

Fig.  864 


There  are  a  number  of  important  advantages  in  this  form  of  palate, 
even  when  made  of  flexible  rubber  and  used  for  the  purposes  of  a 
velum  : 

First.  The  early  deterioration  of  the  rubber,  causing  the  curling  up 
of  thin  edges  of  the  veil,  is  entirely  prevented.  When  this  occurs,  as 
it  frequently  does  with  ordinary  vela,  the  vocal  usefulness  o£  the  palate 
is  impaired — if  not  destroyed — in  proportion  as  it  permits  the  escape 
of  air  at  the  curled-up  portion  of  the  border. 

Second.  The  heavy  border  of  the  veil  is  sufficiently  yielding  and 
flexible  to  be  worn  with  comfort  if  properly  fitted,  and  its  also  presents 


PALATAL  MECHANISM. 


807 


sufficient  stability  and  breadth  of  surface  to  permit  firm  contact  of 
the  pharyngeal  muscles  in  closing  the  naso-pharyngeal  opening. 


Fia.  865 


Third.  In  more  or  less  extensive  clefts  the  thin  central  portion 
extending  forward  into  the  body  of  the  palate  permits  a  resilient  yield- 
ing of  the  lateral  portions  of  the  body,  which  frequently  allows  one  to 


Fig.  866 


spring  it  into  place  with  sufficient  grasp  of  the  irregular  borders,  along 
which  it  should   accurately  fit,  to  hold  it  in  position   without  the  aid 


808  PA  LATA  L    MFJ  'II.  I  A7.S.1/. 

of  supportinjij  ])liite.     WIieneNiT  this  can  he  accoiiiphshcd  with  the  soft 
palate,  it  will  readily  he  continued  when  it  heconies  hanl." 

In  1!K)2  1  constructed  a  new  form  of  instrument  which  apparentlx'  falls 
under  the  term,  "  velum-obturator  "  in  that  it  has  the  compound  action 
of  both.  A  patient  came  into  my  hands  for  a  new  instrument,  the  one 
made  for  her  by  Dr.  Kiuiisley  some  ten  years  previously  having  lost  its 
usefulness.  I  had  known  the  lady  when  her  first  instrument  was  made, 
and  was  well  aware  of  the  improvement  it  had  made  in  her  speech.  I 
was  not  prepared,  however,  for  the  curious  condition  which  I  found  had 
resulted  from  its  use.  The  velum  had  fitted  perfectly  when  first  ad- 
justed, the  palatal  flaps  spanning  the  gap  and  resting  lightly  against  the 
split  soft  palate,  while  the  nasal  flap  rested  above  and  extended  poste- 
riorly in  such  a  way  that  the  sides  of  the  divided  palate,  when  brought 
into  action,  would  slide  between  the  flaps,  and  throw  the  posterior  fiap 
upward,  its  thin  edges  turning  upward  to  occlude  the  passage  of  the  nares, 
this,  of  course,  being  the  intended  object  of  the  Kingsley  velum.  (See 
Fig.  848.)     An  examination,  however,  disclosed  the  fact  that  the  in- 

FiG.  867 


strument  was  not  so  operating.  The  muscles  of  the  pharynx  had  so 
increased  in  activity  that  in  the  closure  of  the  throat  their  contraction 
would  entirely  extrude  the  soft-rubber  ^•elum,  so  that  the  nasal  flap  lay 
constantly  toward  the  palatal  side  of  the  fissure,  and  therefore  became 
merely  a  useless  mass  of  rubber  which  served  no  practical  purpose. 

In  this  dilemma  I  concei\ed  the  idea  of  constructing  an  instrument, 
the  nasal  flap  of  which  should  be  just  the  reverse  of  the  Kingsley  a})i)li- 
ance.  Instead  of  forming  the  nasal  flap  with  thin  tapered  edges,  slightly 
turned  upward  (see  Figs.  845,  846,  847,  849,  and  850),  so  that  in  the 
closing  of  the  throat  these  edges  would  be  everted,  thus  presenting  a 
broad  surface  contact  to  the  walls  of  the  ])harynx,  I  undertook  to  fashion 
a  soft-rubber  a})pliance  with  a  posterior  or  nasal  flaj:),  having  its  most 
posterior  surface  so  formed  that  when  the  pharyngeal  muscles  should 
close  upon  it,  there  would  be  broad  and  equal  surface  contact,  thus 
effectually  occluding  the  passage  to  the  nares,  and  so  obviating  the  escape 
of  sounds  in  that  direction. 

Fig.  867  shows  the  first  instrument  of  this  character  made  by  me. 


PALATAL   MECHANISM.  809 

Comparison  of  tliis  illustration  with  Fig-.  S49  will  show  that  the  nasal 
llaj)  of  my  instrument  is  exaetly  the  re^■erse  of  that  in  Dr.  Kinjisley's. 
In  the  Kingsley  applianee  the  throat  muscles  must  evert  the  tliin  edges 
of  the  velum,  and  so  produce  contact  and  occlusion  of  the  nasal  passages, 
while  in  my  instrument  the  soft-rubber  nasal  flap  is  of  just  such  size 
and  shape  that,  remaining  quiescent,  the  pharyngeal  walls  in  closing 
come  into  accurate  contact  with  it.  Being  made  of  elastic  material,  any 
increased  activity  of  the  throat  muscles  will  be  compensated  for  by  the 
fact  that  the  appliance  is  pliable,  and  in  this  respect  closely  resembles 
the  natural  organs  as  they  are  when  normal. 

It  will  be  seen  at  once  that  the  success  of  such  an  appliance  must 
depend  upon  obtaining  a  model  of  the  parts  which  will  represent  the 
anterior  part  of  the  mouth,  and  the  region  of  the  divided  palate,  as 
they  are  when  absolutely  quiescent,  while  at  the  same  time  the  back 
part  of  the  model  should  give  us  the  exact  form  and  relative  positions 
of  the  pharyngeal  ntuscles  when  endeavoring  to  close  the  throat.  In  this 
act  there  is  left  an  irregular  opening,  which  is  never  symmetrical,  at 
least  in  every  case  that  I  have  obser\'ed  one  muscle  appears  to  be  more 
energetic  than  its  fellow  of  the  opposite  side,  and  it  is  to  this  irregular 
opening  that  the  posterior  surface  of  the  nasal  flap  must  be  made  to 
conform,  so  that  the  throat  in  closing  will  grasp  it  uniformly.  The 
method  of  obtaining  such  a  model  will  be  found  described  in  the  direc- 
tions for  taking  impressions  and  making  models. 

This  first  velum-obturator  made  by  me  encouraged  me  to  believe 
that  by  chance  I  had  stumbled  upon  an  idea  of  value,  because  immedi- 
ately upon  its  introduction  all  nasal  resonance  disappeared  and  articula- 
tion was  restored.  This  statement,  however,  must  be  qualified.  I  have 
heard  many  men,  describing  success  with  their  first  attempts  at  treat- 
ment of  cleft  palate,  declare  that  the  patient  could  speak  perfectly  as  soon 
as  the  instrument  was  introduced.  Such  statements  should  be  recei^-ed 
with  great  scepticism,  as  I  have  never  seen  such  a  result  either  with  my 
own  or  with  Dr.  Kingsley's  patients.  In  this  particular  case,  however, 
we  are  discussing  a  patient  who  had  worn  an  artificial  palate  for  ten 
years,  and  who  had  learned  to  talk  almost  perfectly  with  it.  Then,  with 
the  increased  activity  of  the  pharynx,  and  consequent  displacernent  of 
the  apparatus,  the  Avoman's  speech  had  retrograded  and  the  nasal  reso- 
nance had  almost  entirely  recurred.  It  needed,  therefore,  but  the  intro- 
duction of  an  appliance  which  could  be  kept  in  place  in  spite  of  the  great 
activity  of  the  throat  muscles  to  restore  the  quality  of  her  speaking 
voice. 

It  may  be  well  here  to  explain  more  clearly  what  I  mean  by  the 
"activity"  of  the  throat  muscles,  and  perhaps  I  can  best  do  so  by  stating 
that  with  the  new  appliance  in  place,  and  all  the  tissues  at  rest,  if 
one  looked  down  into  the  pharynx,  the  velum-obturator  would  appear  to 
be  very  much  too  small,  a  space  equal  to  the  diameter  of  a  lead  pencil 
existing  between  the  nasal  flap  and  the  sides  of  the  split  palate.  Yet 
if  with  a  syringe  drops  of  water  were  allowed  to  trickle  into  the  throat, 
compelling  the  act  of  swallowing  (with  the  mouth  open  for  observation), 


810  PALATAL  MECHANISM. 

the  palate  and  pharynx  would  he  seen  to  contract  and  firmly  grasp 
the  posterior  flap. 

This  instrument  has  been  worn  by  this  patient  ever  since  with  such 
satisfaction  that  all  instruments  made  by  me  since  1902  have  been 
made  of  this  form. 

TAKING   THE  IMPRESSION   OF   CLEFT  PALATE. 

No  appliance  made  by  the  dentist  needs  to  be  more  accurately  fitted 
than  an  artificial  palate.  It  is  obviously  a  corollary,  therefore,  that  the 
plaster  model  should  be  as  nearly  as  possible  an  exact  reproduction  of 
the  mouth  which  it  represents. 

To  obtain  such  a  model  requires  skill,  but  not  more  than  should  be 
possessed  by  the  qualified  practitioner.  Yet  the  difficultyof takingthe 
impression  is  the  obstacle  which  has  hindered  many  from  attempting 
to  treat  these  cases,  while  the  ultimate  failure  of  many  others  who  have 
essayed  to  make  instruments  is  directly  traceable  to  their  inaccuracy  in 
this  initial  step. 

The  ordinary  impression  taken  for  artificial  dentures  is  easy,  because 
a  model  is  required  only  of  that  portion  of  the  mouth,  the  tissues  of 
wdiich  overlie  bone.  Therefore,  whether  the  impression  material  be 
introduced  hot  or  cold,  hard  or  soft,  in  large  or  small  quantity,  the  re- 
sultant impression  is  approximately  the  same,  because  of  the  resistance 
offered  by  the  roof  of  the  mouth  against  which  it  is  pressed.  When, 
however,  too  much  material  is  carried  into  the  mouth,  so  that  it  extends 
beyond  the  border  of  the  hard  palate,  the  common  experience  is  what 
is  called  "gagging."  A  consideration  of  what  this  "gagging"  is,  will 
make  more  readily  understood  a  fundamental  principle  involved  in  all 
cleft-palate  cases. 

The  soft  palate  is  sensitive,  and  when  the  impression  material  is 
brought  into  contact  with  it,  the  result  is  an  irritation  or  tickling,  where- 
upon the  involuntary  muscles  of  the  throat  endeavor  to  draw  the  parts 
awa}^  from  the  intruding  substance.  Thus  the  velum  is  elevated,  and 
consequently  w^ere  a  model  to  be  made  from  such  an  impression  it 
would  be  inaccurate  as  to  the  posterior  portion  of  the  mouth,  in  that  it 
would  not  be  a  representation  of  the  parts  at  rest. 

With  the  velum  divided  as  in  cleft  palate,  the  disturbance  of  these 
sensitive  tissues  upon  the  introduction  of  the  impression  material  is 
even  greater.  The  two  halves  of  the  soft  palate  arc  not  only  draw'n  up- 
ward, but  they  also  approach  each  other.  Thus  the  resultant  model 
will  show  the  cleft  narrower  ihan  it  reallij  is  when  the  parts  are  at  rest, 
and  the  pose  of  the  divided  palate  will  be  wrong,  so  that  no  proper  calcu- 
lation can  be  made  for  restoring  the  true  arch  of  the  vault.  This  will 
obtain  whether  the  impression  be  taken  wuth  plaster  of  Paris,  or  with 
impression  compound  softened  by  heat.  Where  the  impression  com- 
pound, however,  is  not  very  soft,  or  where  the  divided  palate  is  lacking 
in  vital  response,  the  impression  material  will  merely  press  the  soft 
tissues  before  it,  the  final  model  being  absolutely  worthless. 

Thus  it  is  seen  that  no  one  can  obtain  an  absolutely  accurate  im- 


TAKING   THE  IMPRESSION  OF  CLEFT  PALATE.  811 

'pression  of  the  divided  velum  in  its  normal  pose.  Nevertheless,  a 
model  may  be  made  which  will  be  as  accurate  as  any  model  of  the  mouth 
can  be. 

The  method  of  procedure  is  as  follows:  select  an  impression  tray  of 
the  ordinary  form,  just  large  enough  to  embrace  the  arch  without 
stretching  the  mouth,  and  long  enough  to  reach  slightly  beyond  the  pos- 
terior border  of  the  hard  palate.  In  the  majority  of  cases  this  will  an- 
swer all  purposes,  but  occasionally,  it  may  be  advantageous  to  extend 
the  cup  by  adding  to  it  a  flap  of  sheet  gutta-percha.  This  may  be  car- 
ried back  as  far  as  the  uvula,  but  should  not  touch  the  velum  at  any 
point.     This  is  to  be  ascertained  by  introducing  the  cup  empty. 

Plaster  of  Paris  is  mixed  in  the  usual  way,  a  little  salt  being  added 
to  hasten  the  setting,  and  warm  water  used  to  render  it  more  accepta- 
ble to  the  mouth.  A  pinch  of  powdered  vermiHon  will  color  the  im- 
pression which  will  aid  in  separating,  and  is  preferable  to  placing  the 
color  in  the  plaster  for  the  model.  The  plaster  is  placed  in  the  tray  in 
quantity  proportionate  to  the  height  of  the  roof,  less  being  used  where 
the  cleft  is  in  the  velum  only,  than  where  the  fissure  enters  the  hard 
palate  also.  The  use  of  too  much  plaster  is  to  be  avoided,  lest  it  es- 
cape and  trickle  down  the  throat.  The  impression  tray  is  to  be  carried 
into  the  mouth  just  as  the  plaster  gives  evidence  of  setting,  and  is  pres- 
sed up  quickly  and  firmly,  and  then  held  steadily  until  sufficiently 
hard  for  removal.  With  a  little  practice  the  calculation  can  be  made 
with  such  nicety  that  the  time  required  will  be  not  more  than  one  min- 
ute. The  plaster  which  remains  in  the  vessel  in  which  it  was  prepared 
will  be  a  guide  to  its  setting,  and  as  soon  as  it  will  fracture  sharply  the 
impression  should  be  withdrawn. 

Where  the  fissure  extends  into  the  hard  palate  it  will  occasionally 
occur  that  the  plaster  which  passes  up  into  the  nasal  cavity  cannot  be 
withdrawn  with  the  impression;  but  if  the  impression  be  removed  at 
the  proper  moment,  the  plaster  will  fracture  along  the  line  of  the  fis- 
sure, and  that  portion  left  up  in  the  nares  may  be  taken  away  with  the 
tweezers. 

Before  passing  to  a  consideration  of  constructing  the  model  one  or 
two  other  points  in  relation  to  the  impression  are  to  be  considered. 

Ordinarily,  all  that  is  required  in  a  model  from  which  to  make  an 
instrument  for  a  cleft-palate  patient  will  be  absolute  accuracy  as  to  the 
oral  aspect  of  the  parts  and  the  borders  of  the  fissure  from  its  apex  to 
the  uvulse.  It  will  very  rarely  be  essential  to  procure  a  perfect  impres- 
sion of  the  upper  or  nasal  side,  except  that  the  operator  should  observe 
the  thickness  of  the  tissues  along  the  borders  of  the  cleft,  the  position 
of  the  vomer,  and  whether  it  is  likely  to  interfere  with  the  design  of  the 
instrument,  as  it  often  will  where  the  fissure  only  slightly  enters  the  hard 
palate.  In  such  cases  it  becomes  important  to  know  how  close  the  in- 
sertion of  the  vomer  is  to  the  border  of  the  cleft  at  the  apex.  This  is 
readily  accomplished  by  placing  a  small  quantity  of  plaster  up  into  the 
nasal  cavity  at  the  apex  of  the  fissure,  carrying  it  into  place  with  a 
narrow-bladed  knife,  or  other  suitable  instrument,  just  before  intro- 
ducing the  impression.     This  may  come  away  with  the  impression,  or 


812  PALATAL  MECHANISM. 

it  may  fracture  and  remain  in  place,  in  which  case  it  is  to  l)e  remo\ed 
with  tweezers  and  added  to  tlie  impression. 

Where  the  fissure  partly  enters  the  hard  palate,  as  has  been  already 
stated,  the  exact  position  of  the  vomer  must  be  com])rehended.  The 
reason  is  that  where  an  artificial  velum  is  used,  it  engaoes  the  fissure,  so 
that  a  flap  extends  slightly  over  the  border  at  the  apex  on  the  nasal 
side.  In  some  cases  the  insertion  of  the  vomer  into  the  hard  palate  is 
so  near  to  the  border  at  the  apex  that  the  artificial  velum  might  rest 
against  it  and  cause  irritation,  unless  provision  be  made  to  guard 
against  this.  But  the  simple  method  of  carrying  a  little  plaster  through 
the  fissure  at  this  point  l)efore  inserting  the  impression,  as  previously 
described,  accomplishes  the  recjuired  result  perfectly. 

Where  the  fissure  involves  the  whole  or  greater  part  of  the  hard 
palate  it  may  occasionally  be  required  to  secure  an  accurate  model  of 
the  nasal  cavity  as  well  as  of  the  oral. 

The  impression  here  is  obtained  by  carrying  the  plaster,  mixed  fairly 
stiff,  up  into  the  nasal  cavity,  filling  it  to  the  borders  of  the  fissure, 
whereupon  the  tray  with  additional  plaster  is  carried  to  place.  As  the 
plaster  in  the  tray  unites  with  that  which  is  in  the  nares,  great  care  must 
be  observed  to  remove  the  impression  at  the  first  moment,  when  a 
sharp  fracture  is  possible.  With  a  sudden  sharp  movement  the  impres- 
sion comes  away,  leaving  the  plaster  in  the  nares,  the  fracture  along  the 
borders  of  the  fissure  being  sharp  and  clean,  so  that,  when  the  nasal 
portion  is  removed  by  sliding  it  back  tovv^ard  the  throai  and  allowing  it 
to  drop  down  upon  the  tongue,  it  is  readily  replaced  in  proper  position 
upon  the  impression.  If  the  operator  is  timid  about  attempting  this, 
after  filling  the  nares  Avith  plaster  he  may  allow  it  to  set.  Then  after 
oiling  the  exposed  portion  of  the  plaster,  which  now  finishes  out  the 
arch  of  the  roof,  the  impression  may  l)e  completed  without  danger  of 
the  two  parts  adhering.  For  the  purpose  of  obtaining  an  accurate 
impression  of  the  margins  of  the  fissure,  the  late  Prof.  CJeorge  T.  Bar- 
ker recommended  the  use  of  a  piece  of  soft  sponge  cut  to  approximate 
the  size  of  the  fissure,  first  having  been  made  pliable  by  immersion  in 
warm  water,  wrung  out,  and  then  saturated  with  plaster  of  Paris  mixed 
thin.  The  sponge  so  prepared  is  then  cjuickly  carried  into  the  fissure 
and  allowed  to  remain  until  the  plaster  has  fully  hardened,  when  it  can 
be  readily  removed  without  force  by  means  of  suitable  tweezers.  The 
portion  corresponding  to  the  roof  of  the  mouth  may  then  be  trimmed 
smooth,  varnished,  oiled,  and  replaced.  The  impression  with  the  cup 
may  then  be  completed  without  injury  to  the  delicate  edges  of  the  fis- 
sure. 

It  will  w^e  w'ell  for  those  who  wish  to  utilize  Dr.  (^ase's  appliance  to 
follow  his  owm  mode  of  taking  his  impression,  which  he  describes 
as  follows  ; 

"  In  taking  an  impression  for  the  construction  of  this  palate  where 
the  cleft  is  extensive  or  even  extending  somewhat  into  the  hard  palate, 
it  is  my  object  to  obtain  a  perfect  model  of  that  portion  of  the  roof  of 
the  mouth  over  which  I  wish  the  palatal  portion  of  the  ])late  to  extend, 
and  along  the  borders  of  the  cleft  forward  of  the  pendent  portions  of 


TAKING   THE  IMPRESSION  OF  CLEFT  PALATE. 


813 


the  velum  palati,  extending  somewhat  upon  the  floor  of  the  nares  and 
representing  as  perfectly  as  possible  the  liasal  borders  of  the  cleft  and 
lateral  surfaces  of  the  posterior  nares. 

These  surfaces,  a  part  of  which  lie  above  the  pendent  and  unstable 
tissues  of  the  velum  palati,  are  frequently  susceptible  of  being  perfectly 
reproduced  in  the  model  of  a  plaster  impression.  It  will  usually  be 
found  in  a  typical  case  that  the  posterior  nasal  openings  are  laterally 
constricted,  from  which  point  the  nasal  fossiB  widen  to  form  the  floor 
of  the  nares.  By  obtaining  a  perfect  impression  of  these  somewhat 
unyielding  surfaces,  which  otherwise,  on  account  of  their  position, 
would  be  very  difficult  to  reproduce,  the  anterior  borders  of  the  arti- 
ficial veil  can  be  perfectly  fitted  to  them  as  they  merge  into  the  nasal 
borders  of  the  body. 

I  lay  particular  stress  upon  this  portion  of  the  operation  because  I 
have  found  it  important,  not  only  as  a  great  aid  to  the  proper  action 
of  the  pharyngeal  muscles,  but  in  clefts  of  considerable  extent  the 
overhanging  nasal  borders  of  the  artificial  palate  can  be  easily  sprung 
into  place,  and  when  fitted  perfectly  patients  soon  learn  to  place  and 
sustain  the  palate  without  the  aid  of  a  supporting  plate. 

I  would  advise,  however,  that  the  supporting  plate  be  always  made, 
to  enable  patients  to  more  readily  adjust  and  sustain  the  plates  until 
they  have  learned  to  wholly  do  without  it. 

Fig.   868. 


When  no  artificial  teeth  are  required,  or  when,  if  required,  a  bridge 
denture  is  practicable,  the  supporting  plate  should  be  made  to  cover 
as  small  an  area  of  the  roof  of  the  mouth  as  is  consistent  with  the 
demand  for  strength,  I  rarely  extend  it  forward  of  the  second 
bicuspid,  leaving  as  much  of  the  anterior  palatal  surface  exposed  as 
possible,  which  I  believe  materially  aids  in  acquiring  perfect  enun- 
ciation. 

Fig.  868,  which  is   made  from  the  model   of  an   impression  of  the 


814 


FA  LA  TA  L  MECHANISM. 


mouth  with  tlie  apparatus  in  place,  shows  the  form  of  the  supporting 
phite  I  usually  make. 

There  are  two  ways  of  taking  these  impressions:  One  by  forming 
a  base  of  modelling  compound  upon  which  to  lay  the  plaster,  and  the 
other  by  using  plaster  alone. 

For  the  first  the  compound  is  wrapped  around  the  forefinger  (Fig. 
S69),  and  pressed  gently  to  place.  Removing,  softening,  and  perhaps 
slightly  reshaping  and  cutting  away  surplus,  this  is  repeated  several 
times,  with  the  view  of  finally  obtaining  a  modelling  compound  impres- 


FiG.  869 


Fig.  870 


sion  that  will  not  displace  the  soft  posterior  borders,  and  that  will  per- 
fectly support  the  plaster  for  the  final  impression.      (Fig.  870.) 

The  palatal  surface  is  then  roughened  so  the  plaster  will  cling  to  it, 
and  all  that  portion  of  the  compound  which  extends  above  the  nearest 
approaching  borders  of  the  cleft  is  cut  away  and  the  cut  surface 
smoothed  and  oiled.      (Fig.  871.) 

This,  when  carried  to  place  with  the  plaster  in  position,  need  cause 


Fig.  871 


Jig.   S72 


no  fear  of  its  ea.sy  removal,  even  though  an  excess  o>  plaster  is  used — 
providing  it  does  not  come  forward  of  the  alveolar  ridge  in  extensive 
double  clefts — as  all  that  portion  which  extends  above  the  border  of  the 
cleft  forming  the  impression  of  the  nasal  fosste  will  readily  break  from 
the  .smooth,  oiled  surface  of  the  compound,  when  the  impression  is 
removed,  it  being  otherwise  unattached  to  the  lower  part.s,  as  the  com- 


TAKING   THE  IMPRESSION  OF  CLEFT  PALATE. 


815 


])()un(i  completely  bridges  the  cleft  from  its  nearest  approaching  bor- 
deis.  The  nasal  section  can  then  be  teased  back  toward  the  more 
open  portion  of  the  cleft,  and  allowed  to  fall  on  a  mouth  mirror,  from 


Fig.  873 


Fig.  874 


which  it  is  replaced  upon  the  impression.     (Fig.  872.)     Figs.  873-875 
show  different  views  of  a  plaster  impression  taken  this  way. 

As  a  rule,  I  prefer  plaster  alone,  dividing  it  as  above  in  sections  at  the 
borders  of  the  cleft.     Figs.  876-878  show  different  views  of  an  impression 


Fig.  875 


Fig.  876 


of  a  cleft  taken  entirely  with  plaster.  The  first  section  is  passed  freely 
into  the  nasal  cavity  with  a  spatula,  stopping  it  abruptly  at  the  nearest 
approaching  border  of  the  cleft.  The  under  surface  is  then  lubri- 
cated with  a  solution  of  white  vaseline,  and  the  first  part  of  the  second 


Fig.  877 


Fig.  878 


section  is  delicately  laid  on  Avith  the  spatula,  so  as  to  not  lift  or  dis- 
lodge the  upper  section.  The  plaster  is  spread  out  over  the  roof  of 
the  mouth  with  a  spatula,  and  when  partially  hard  is  strengthened  for 


816  PALATAL  MECHANISM. 

removal  with  fresh  plaster  introduced  in  a  flat  impression  tray.  The 
impression  does  not  need  to  extend  even  to  the  gingival  borders  of  the 
teeth. 

In  filling  and  trimming  the  easts  from  these  impressions,  nearly  all 
that  portion  back  of  the  attachments  of  the  soft  palate  is  cut  away, 
and  the  nasal  portion  of  the  cast  open  and  freely  exposed  to  the  extreme 
nasal  borders,  produced  by  the  impression. 

This  is  done  to  facilitate  shaping  the  modeling  compound  model  or 
pattern  of  the  palate,  and  its  ready  removal  from  and  replacing  upon 
the  cast  during  the  process  of  repeated  trials  in  the  mouth. 

Fig.  879  shows  palatal  view  of  the  finished  model.  The  nasal  view 
would  look  very  similar." 

In  cases  where  there  has  been  an  operation  upon  the  lip  the  mouth 
v/ill  sometimes  be  so  contracted  as  to  preclude  the  possibility  of  in- 
troducing a  full  impression  tray,  one  that  would  extend  over  and  in- 
clude the  teeth.  Usually,  however,  a  tray  may  be  introduced  if  cut  away 
so  as  just  to  cover  the  occlusal  surfaces  of  the  teeth,  the  removal  of  the 
outer  rim  allowing  its  introduction  with  less  stretching  of  the  mouth. 
An  impression  thus  procurefl  will  give  a  model  showing  the  roof  of  the 
mouth  and  the  cleft,  the  palatal  surfaces  of  the  teeth  and  part  of 
their  occlusal  surfaces.  In  order  to  perfect  such  a  model  the  correct 
shape,  forms  and  positions  of  the  teeth,  may  be  secured  in  the  following 
manner.     A  second  impression  is  taken  of  one-half  of  the  upper  jaw 


using  an  ordinary  crown- and  bridge-work  tray.  Care  should  be  ob- 
served to  include  if  possible  the  central  incisors.  From  the  original 
model  the  greater  portion  of  each  plaster  tooth  is  cut  off,  and  the  outer 
part  of  the  model  roughened  with  a  knife.  The  new  imj)ression  is 
now  fitted  to  the  model,  and  will  ])e  found  accurately  iidaptcd,  and  it 
may  be  held  fast  with  sticky  wax.  New  plaster  is  j)()ured  into  the  im- 
pression and  against  the  model.  "When  this  has  hardened  the  impres- 
sion is  removed,  and  the  model  will  be  found  complete  on  one  side.  A 
similar  procedure  will  com])lete  the  model  on  the  other  side,  and  the 
precaution  of  securing  both  centrals  will  be  found  an  aid  in  T)lacing  this 


TAKING   THE  IMPRESSION  OF  CLEFT  PALATE.  817 

last  impression  in  position.  Fig.  880  is  from  a  model  thus  made,  and 
the  plate  made  from  this  model  accurately  fitted  the  mouth. 

In  accidental  fissures  resulting  from  disease  or  other  cause  we  some- 
times find  merely  an  aperture  in  the  palate,  which  may  be  quite  small. 
In  taking  an  impression  the  plaster  would  ooze  through  this  hole  and 
form  a  knob  or  button  upon  the  upper  side,  which,  of  course,  would 
remain  after  the  removal  of  the  impression-cup.  Then,  as  the  posterior 
portion  of  the  soft  palate  would  be  normal,  it  might  become  a  very  dif- 
ficult matter  to  remove  this  plaster  without  permitting  it  to  pass  down 
into  the  pharynx.  In  these  cases  the  precaution  should  be  taken  to  lay 
across  the  aperture  a  bit  of  Japanese  tissue-paper  folded  two  or  three 
times.  This  paper  will  yield  sufficiently  to  allow  the  plaster  to  take  a 
perfect  impression,  yet  resist  its  passage  through. 

Wliere  the  ravages  of  disease  may  have  been  very  extensive,  a  case 
may  present  in  which  the  palatal  separation  of  the  nasal  and  oral 
cavities  may  be  entirely  absent,  and  the  two  being  practically  one,  oc- 
casionally irregularities  and  convolutions  present  which  make  it  desir- 

FiG.  SSO 


able  to  proceed  without  first  procuring  a  complete  model  of  the  parts. 
The  procedure  is  as  follows:  A  sheet  of  gutta-percha  is  softened  and 
trimmed  to  approximately  cover,  let  us  say,  the  right  half  of  the  cavity 
extending  below,  over  the  alveolar  ridge,  or  teeth,  if  these  organs  be  pre- 
sent. Using  this  as  a  tray  an  impression  of  the  right  half  is  easily  pro- 
cured, and  a  model  made.  On  this  model  a  wax  plate  is  fashioned  and 
reproduced  in  vulcanized  rubber.  This  rubber  plate  is  tried  in  the 
52 


818  PALATAL   MECHANISM. 

mouth,  and  any  angles  that  might  cause  irritation  or  render  removal 
difficult  arc  carefully  filed  away,  until  the  plate  rests  comfortably 
against  the  right  half.  With  this  in  j)lace,  plaster  is  then  pressed  against 
the  left  side  and  partly  over  the  rubber  i)late.  When  hard  the  two  are 
removed  separately,  waxed  together,  and  a  model  made  over  them  both. 
A  plate  of  vulcanite  is  now  made  for  the  left  side,  both  being  united  in 
the  vulcanization,  so  that  we  now  have  a  shell  of  thin  vulcanite  rubber 
wliich  will  fit  the  whole  interior  of  the  cavity.  This  is  next  filled  with 
plaster  carved  so  as  to  form  a  representation  of  a  normal  vault  when 
in  place.  With  this  surface  oiled  to  prevent  adhesion  of  new  plaster, 
the  shell  with  its  filling  of  plaster  is  placed  in  the  mouth  and  an  impre.s- 
.sion  taken  as  of  a  normal  mouth.  The  model  from  this  will  have  the 
shell  of  vulcanite  in  place,  and  still  retaining  the  filling  of  plaster. 
Using  this  as  any  regular  model,  a  set  of  teeth  (if  teeth  be  required) 
is  made,  and  in  the  course  of  vulcanization  this  final  rubber  plate  attaches 
to  the  shell  whicii  lines  the  upper  cavity.  On  removal  from  the  flask  a 
hole  is  cut  opposite  the  iioslrils,  and  another  at  the  back,  and  through 
these  holes  the  plaster  filling  is  dug  out,  leaving  a  set  of  teeth,  having  a 
hollow  superstructure  of  vulcanite  which  closely  fits  against  all  the  upper 
surfaces.  A  plate  of  this  character  usually  stays  in  place  quite  fixedly. 
The  two  holes  supply  breathing  apertures. 


PERFECTING    THE    MODEL. 

The  model  made  from  the  most  accurate  impression  will  represent 
the  cleft  with  its  sides  drawn  somewhat  together  and  possibly  pressed 
backward.  The  next  step,  therefore,  will  be  the  correction  of  these 
errors,  and  the  production  finally  of  a  model  which  will  be  an  accurate 
reproduction   of  the   mouth. 

When  the  chapter  for  the  first  edition  of  this  work  was  written  it  was 
my  opinion  that  after  obtaining  the  model  from  the  impression,  the  fur- 
ther correction  of  the  same  might  be  confined  to  the  outline  of  the  bor- 
ders of  the  cleft,  but  the  necessities  of  three  or  four  extreme  cases 
which  have  passed  through  my  hands  since  that  time  have  materially 
altered  my  views  on  this  subject. 

First,  however,  I  may  describe  how  the  proper  shape  and  outline  of 
the  cleft  itself  is  to  be  »ibtained.  A  trial  plate  is  made  of  gutta-percha, 
and  as  it  must  be  quite  stifi"  to  adequately  serve,  it  is  best  to  use  two 
sheets.  The  first  sheet  may  be  fitted  to  the  model  as  it  stands  after 
removal  from  the  original  impression.  An  extension  of  this  trial  plate 
is  trimmed  to  just  lie  within  the  cleft  as  it  appears,  or  within  as  much 
of  it  as  is  shown;  sometimes  only  a  part  of  the  fissure  is  disclosed  in  the 
first  model.  A  second  piece  of  gutta  percha  of  similar  pattern  is  cut, 
to  be  warmed  and  pressed  into  place  over  the  first;  before  doing  so,  how- 
ever, a  piece  of  copper  or  tinned  iron  wire  is  formed  into  a  loop  and 
pressed  into  the  first  layer  of  gutta-percha,  the  loop  running  down  into 
the  extension  which  fits  into  the  cleft.     The  second  layer  of  gutta-percha 


PERFECTING    THE  MODEL.  819 

is  then  placed  over  the  first,  and  this,  with  the  wire  loop  between ,  fur- 
nishes a  stiff  trial  plate,  which  may,  however,  be  bent  as  desired.  If 
this  be  tried  in  the  mouth,  two  facts  at  once  appear.  The  natural 
cleft  will  be  seen  to  be  wider  than  that  in  the  plaster  model,  as  indi- 
cated by  the  width  of  the  trial  plate  extension.  Second,  the  sides  of 
the  natural  cleft  now  fall  down  much  below  the  gutta-percha  extension, 
proving,  as  elsewhere  claimed,  that  the  divided  palate  is  drawn  up 
during  the  intrusion  of  the  plaster  impression.  The  tail  piece  is,  there- 
fore, bent  down  until  it  exactly  follows  the  true  curve  of  the  natural 
palate,  when  the  two  halves  are  at  rest,  and  it  will  occasionally  take  some 
patience  to  ascertain  this,  as  the  sensitive  sides  of  the  cleft  palate  will 
often  flutter  for  a  very  long  time  before  coming  to  rest.  But  with  per- 
sistency in  keeping  the  mouth  open,  the  muscles  finally  tire  and  remain 
at  rest.  Next  wax  must  be  added  to  the  sides  of  the  tail  piece  and  re- 
peatedly tried  in  the  mouth,  until  it  is  seen  that  the  tail  piece  is  so  shaped 
that  when  at  rest  the  divided  palate  just  touches  it  at  all  parts.  This 
then  furnishes  an  accurate  guide  to  the  exact  shape  and  curve  of  the 
natural  palate.  This  is  placed  on  the  model,  when  it  will  be  found  neces- 
sary to  cut  away  the  plaster  along  the  edges  of  the  cleft,  until  the  extra 
width  of  the  re-modeled  tail  piece  drops  into  place.  The  edges  of  the 
plaster  model  are  next  built  up  to  the  gutta-percha  guide  with  plaster 
carried  on  a  camel's  hair  pencil.  The  plaster  should  be  extremely 
thin,  and  the  model  wet,  else  it  will  be  difficult  to  work.  In  this  man- 
ner the  sides  of  the  cleft,  and  even  the  divided  uvula,  may  be  quite 
accurately  reproduced. 

A  model  of  this  character  will  suffice,  where  an  obturator  is  to  be 
supplied,  for  as  will  be  seen  elsewhere,  further  impressions  of  the  pharyn- 
geal portion  become  a  part  of  the  technique  of  procuring  the  model 
for  the  obturator.  Moreover  I  had  until  recently  thought  that  such  a 
model  would  suffice  where  a  velum  is  to  be  made,  because  ordinarily 
the  velum  may  be  made  sufficiently  small  so  that  at  first  it  is  readily 
tolerated,  and  it  is  no  difficult  matter  to  alter  the  molds  so  as  to  lengthen 
or  widen  the  velum  subsequently,  as  may  be  seen  to  be  required. 

But  cases  have  passed  through  my  hands  where  the  activity  of  the 
muscles  was  so  great  that  in  the  act  of  swallowing  the  pharvngeal 
muscles  approach  each  other  to  such  an  extent  as  to  almost  occlude  the 
nares.  In  such  cases  it  becomes  absolutely  requisite  to  obtain  a  perfect 
model  of  the  phajATix,  not  in  its  normal  state  of  rest,  hut  as  it  ci'ppears 
when  closed,  as  in  the  act  of  sicalloicing,  for  it  is  manifest  that  the  size 
and  shape  of  any  instrument  inserted  in  such  a  throat  must  largely  be 
regulated  by  the  position  of  the  muscles  when  thus  drawn  towards' one 
another,  as  well  as  by  the  aperture  that  may  be  left. 

We  aim  then  to  obtain  a  model  which  will  show^  all  the  mouth  parts 
as  they  are  when  in  a  normal  state  of  rest,  while  the  pharyngeal  portion 
must  be  seen  in  the  same  model  as  it  appears  when  contracted  as  in 
the  act  of  swallownng.  Occasionally  it  may  be  requisite  to  proceed  as 
in  making  an  obturator,  and  at  this  point  make  the  platinum  carrving 
plate.     This  necessity  vn\\  only  arise  wdien  the  patient  finds  it  difficult 


820  PALATAL  MECHAiilSM. 

to  swallow  while  the  operator  holds  one  finger  in  the  mouth  to  steady 
the  trial  plate. 

The  tail-piece  of  the  trial  plate  is  extended  until  it  nearly,  but  not 
quite,  touches  the  posterior  wall  of  the  pharynx.  A  bit  of  sheet  wax  is 
then  added  to  the  extremity  and  turned  upward;  this  will  be  better 
comprehended  when  it  is  explained  that  it  is  to  serve  to  prevent  the 
passage  of  plaster  down  the  throat.  Along  the  upper  side  of  the  tail 
piece  other  pieces  of  wax  are  atlded  to  form  a  sort  of  box,  to  hold  plas- 
ter. This  is  then  tried  in  the  mouth  and  the  patient  made  to  swallow, 
until  the  operator  is  satisfied  that  his  added  wax  in  no  way  hinders 
this  action.  Plaster,  with  very  little  salt,  is  then  mixed  quite  thin  and 
piled  up  on  top  of  the  tail  piece  which  is  then  quickly,  and  skilfully 
adjusted,  care  being  observed  not  to  spill  the  plaster  into  the  throat, 
thus  producing  gagging.  The  patient  is  then  made  to  swallow  forcibly 
two  or  three  times,  and  then  asked  to  remain  as  quiet  as  possible.  As 
soon  as  the  plaster  hardens  the  trial  plate  (see  Fig.  898)  is  removed,  and  is 
then  placed  in  position  on  the  model.  I  may  say  here  parenthetically 
that  when  from  the  extreme  activity  of  the  throat  muscles  the  operator 
decides  that  this  procedure  will  be  required,  it  is  best  to  take  this  step 
prior  to  perfecting  and  completing  the  shaping  of  the  borders  of  the  cleft. 
The  plaster  used  to  take  this  impression  of  the  contracted  pharynx  should 
have  some  coloring  matter  (powdered  water  color  paint  added  to  the 
water)  in  order  to  facilitate  separation,  and  it  should  be  thoroughly 
soaped.  With  the  trial  plate  it  is  then  placed  in  proper  position,  and 
plaster  mixed  quite  thin  is  added  to  the  original  model  from  the  pos- 
terior end. 

When  removed  the  model  resulting  gives  a  perfect  representation  of 
the  teeth  and  soft  tissues  supported  by  bone;  of  the  cleft  palate  as  it 
is  when  normally  at  rest  and  of  the  pharynx  when  closed  as  in  the 
act  of  swallowing.  It  is  from  such  a  model  that  I  make  my  modified 
Kingsley  velum,  which  is  really  in  its  action  what  Dr.  Case  calls  a  velum 
obturator. 

THE    MAKING   OF   ARTIFICIAL   VELA. 

With  an  accurate  model  from  which  to  work  an  artificial  velum  could 
be  made  without  further  reference  to  the  patient,  though  it  might  be 
best  for  the  inexperienced  to  try  in  the  model  of  the  velum  before  pro- 
ceeding to  the  construction  of  metal  molds. 

The  first  step  in  the  production  of  the  Kingsley  velum  will  be  to  make 
a  model  of  the  palatal  flap.  The  model  of  the  velum,  if  it  is  not  to  be 
tried  in  the  mouth,  may  be  made  of  wax,  otherwise  it  will  be  best  to  use 
sheet  gutta-percha.  The  palatal  flap  is  a  triangle  with  rounded  an- 
gles. The  apex  of  this  triangle  coincides  with  the  apex  of  the  fissure, 
and  the  base  extends  across  from  one  uvula  to  the  other.  This  flap 
should  be  made  just  large  enough  to  bridge  the  gap,  as  it  will  be  easy 
to  widen  it  later  by  scraping  the  mold  should  it  become  needful,  whereas 
if  made  too  large   at  the  outset,  it   might   become    necessary  to  make 


THE  MAKING   OF  ARTIFICIAL  VELA. 


821 


a  part  of  the  mold  over.  The  pattern  of  the  flap  having  been  cut  out 
from  g'utta-perc'ha,  it  is  to  be  sHghtly  softened  and  then  pressed  against 
the  model,  so  that  it  assumes  the  proper  form  to  lie  close  to  the  surface 
of  the  latter.  It  will  often  occur  that  the  edges  of  the  natural  cleft  are 
rounded  or  rope-like,  thus  showing  a  depression  between  the  border  of 
the  cleft  and  the  maxillary  bone.  In  these  cases  the  upper  flap,  when 
molded  upon  the  model,  will  assume  quite  a  curl  or  crimp,  especially 
near  the  uvulae.  If  the  model  is  accurate  and  the  flap  is  made  to  prop- 
erly conform  to  this  peculiarity,  when  placed  in  the  mouth  it  will  lie 
close  against  the  soft  tissues.  Were  it  left  comparatively  a  plane,  the 
edges  would  stand  off  and  be  quite  noticeable  to  the  tongue.  This 
curling  is  made  more  apparent  because  of  the  fact  that  the  flap  is  slightly 
depressed  between  the  sides  of  the  cleft,  so  that  it  forms  a  piart  of  the 
arch  of  the  mouth  and  completes  it.  As  soon  as  the  flap  has  been 
molded  into  proper  form,  all  the  edges  being  quite  thin,  it  is  plunged 
into  cold  water,  so  that  it  shall  retain  its  shape. 


Fig.  881 


.  ^^i^^--"-- 

'iilL 

^ 

'   ^I^^H^^^^K^ 

^•^^^^^H^^^^H^^^^K ' 

1 

m^^__-Hri 

I^^IBf             ''"^I^Hf^B 

Jf 

m'KFSj 

W     '          %     ^ 

^^m 

^^ 

^ 

The  second  or  upper  flap  is  molded  upon  the  model  in  a  similar 
manner,  the  form  being  ugain  triangular.  But  the  base  must  now  be 
fashioned  so  that  its  posterior  edge  will  meet  the  ridge  of  the  pharynx 


822 


PA  LA  TA  ;.   MI'X  'HA  NISM. 


at  a  slight  aii,<i;l('.  Tlic  ficiuTal  adaptation  of  the  flaj)  to  the  niodol  hav- 
in<,f  been  ohtaiiu-d,  it  is  placed  in  position,  and  the  model  and  flap  firmly 
held  in  the  left  hand,  while  with  the  thumb  and  forefinger  of  tlie  right 
hand  the  oj)erator  grasps  the  flap  at  the  centre  of  the  posterior  part 
and  simply  bends  it  up,  whereupon  it  assumes  the  form  shown  in  Figs. 
845-847.  Usually  the  guide  for  bending  this  tail-piece  is  to  form  a 
margin  so  that  the  plane  of  that  surface  will  be  on  a  line  with  the 
incising  edges  of  the  anterior  teeth. 

The  two  flaps  are  next  placed  upon  the  model  at  the  same  time  and 
waxed  together  with  hard  wax.  The  velum  is  then  ready  to  be  tried  in 
the  mouth,  when  the  operator  may  correct  any  discrepancies  as  to  fit  in 
length. 

The  model  of  the  velum  having  been  satisfactorily  made,  it  becomes 
necessary  to  produce  metal  molds  in  which  soft  rubber  may  be  vulcan- 
ized into  the  desired  form. 

A  convenient  form  of  flask  for  liolding  these  molds  is  round  and  in 
two  parts,  one  of  which  has  a  stjuare  hole  cut  at  the  centre. 


FiG.  SS2 


In  constructing  the  molds  the  model  of  the  v(>hnn  is  placed  in  that 
half  of  the  flask  which  has  the  hole,  so  that  the  smaller  or  ))alatal  flap 
rests  over  the  hole.  The  llask  having  been  freely  oiled,  plaster  is  poured 
into  it  and  around  the  model.  AVhen  hard  it  is  knocked  out  readily 
and  carved  into  shape.     It  is  then  varnished,  replaced  in  the  flask,  and 


THE  MAKfNG    OF  ARTIFICIAL    VFLA. 


823 


oiled.  Tlir  model  of  the  velum  still  being-  in  position,  plaster  is  poured 
over  it  and  the  plaster  mold  whieh  now  surrounds  it,  and  the  opposite 
half  of  the  flask,  well  oiled,  is  put  on  and  pressed  firmly  to  plaee. 
When  this  is  hard  and  separated  the  two  parts  of  the  mold  are  com- 
plete. The  third  is  made  by  pouring  plaster  through  the  hole  in  the 
top  of  the  flask,  completely  fllling  the  space  left  within  the  flask,  and 
covering  the  top  flap.  These  three  pieces  of  plaster  are  then  repro- 
duced by  molding  in  sand  and  casting  in  type-metal.  The  general 
appearance  when  complete  is  shown  in  the  accompanying  illustrations. 
Fig.  SSI  is  the  bottom-piece,  in  which  a  pin  appears;  this  is  best  made 
of  iridio-platinum  wire,  and  is  driven  into  a  drilled  hole  after  the  model 


Fig.  SS3 


is  cast.  In  some  .cases  it  will  be  tight  enough,  but  occasionally  it  may 
be  requisite  to  fasten  it  with  soft  solder.  Its  purpose  is  to  produce 
a  hole  in  the  velum  through  which  the  bar  on  the  plate  passes.  The 
two  aspects  of  the  central  piece  of  the  mold  are  shown  in  Figs.  882 
and  883,  while  Fig.  884  shows  the  top-piece.  The  surfaces  for  mold- 
ing the  rubber  are  to  be  smoothed  with  a  pine  stick  and  pumice.  The 
metal  molds  are  returned  to  their  respective  positions  in  the  flask  sec- 
tions. 

In  \'ulcanizing  the  soft  rubber  it  is  well  to  slightly  soap  the  surface 
of  the  molds  before  packing,  as  this  facilitates  removal  after  vulcaniza- 
tion, and  avoids  a  tendency  on  the  part  of  the  rubber  to  adhere  to  the 


824 


PALATAL  MECHANISM. 


metal,  especially  should  any  rou^li  i)laces  be  left,  which  of  course 
should   be  avoided. 

The  flask  should  be  opened  and  excess  of  rubber  removed;  otherwise 
it  will  be  pressed  ajjainst  the  unpolished  portions  of  the  mold,  and  ren- 
der it  extremely  difficult  to  open  the  flask  after  vulcanization.  As  soft 
rubber  swells  considerably  during  vulcanization,  the  mold  need  not  be 
quite  full,  but  care  should  be  taken  to  avoid  creases  in  the  rubber,  as 
they  will  not  be  filled  out  however  much  the  rubber  may  swell,  prob- 
ably owing  to  the  imprisonment  of  air. 

The  best  results  in  the  vulcanization  of  soft  rubber  are  obtained  by 
observing  the  following  directions:  Place  charcoal  or  other  substance  in 
the  bottom  of  the  vulcanizer  high  enough  to  stand  above  the  water 
which  is  poured  in.  Allow  the  flask  to  rest  upon  this  charcoal.  In  this 
manner  the  rubber  is  vulcanized  in  steam. 


Fig.   884 


The  thermometer  which  registers  the  heat  should  indicate  240°  for 
two  hours;  250°  for  one  hour;  260°  for  one  hour;  and  270°  for  one 
hour. 

The  velum  when  taken  from  the  flask  will  have  a  peculiar  odor  if 
overdone,  as  though  it  had  been  burned.  In  that  case,  however  per- 
fect and  elastic  it  may  appear,  it  will  be  worthless  within  a  very  few 
weeks. 


CONSTRUCTION  OF  THE  OBTURATOR. 


825 


THE    CONSTRUCTION   OF   AN   OBTURATOR. 

An  obturator  may  be  made  for  a  patient  where  the  cleft  involves  the 
soft  palate  only,  but  will  be  more  commonly  resorted  to  where  both  soft 
and  hard  palates  are  fissured.  The  process  in  connection  with  the 
latter  condition  is  described,  as  it  is  the  more  intricate. 

A  correct  model  having  been  obtained,  the  fissure  in  the  hard  palate 
is  filled  with  wax,  so  that  the  arch  of  the  vault  is  restored.  Dies  are 
made  and  a  plate  of  iridio-platinum  swaged  to  fit  this  reconstructed 
model,  with  the  result,  of  course,  that  when  carried  to  the  mouth  it 


Fig.  885 


bridges  over  the  gap  in  the  hard  palate.  The  plate  is  provided  with  an 
extension  at  the  posterior  part  which  shall  support  the  obturator,  and  it 
is  attached  to  the  teeth  by  gold  clasps.  For  this  purpose  it  is  best  to 
rely  upon  the  sixth-year  molars  as  offering  the  best  anchorage,  and 
where  these  teeth  are  badly  decayed  it  is  often  advisable  to  crown  them 
with  gold  before  fitting  the  clasps  about  them.  Thus  the  anchorages 
may  be  permanently  protected  against  loss  by  decay. 

Where  crowns  are  used  it  will  be  found  most  advantageous  to  use  the 
clasp  invented  by  Dr.  Emory  A.  Bryant,  as  this  device  not  only  holds 
a  plate  firmly  in  place  but  prevents  tilting  during  the  action  of  swallow- 
ing. To  construct  a  clasp  of  this  character,  after  the  crowns  are  made 
they  are  loosely  fitted  over  the  natural  teeth  or  roots  which  they  are  to 
cover,  and  an  impression  taken,  which  of  course  removes  them  when 


826  PA  LA  TA  L  M  KCHA  XISM. 

withdrawn  from  the  mouth.  Plugs  of  pine  wood  are  fitted  witli  moder- 
ate accuracy  into  the  crowns  shghtly  protruding  thereform,  and  the 
model  is  then  poured.  By  this  precaution  the  crowns  are  easily  re- 
moved and  replaced  upon  the  model.  With  any  of  the  many  parallel- 
ing devices,  parallel  lines  are  scratched  on  the  l)uccal  surfaces  of  the 
gold  crowns,  and  along  each  line  is  soldered  a  piece  of  iridio-platinum 
wire.  The  clasp  is  made  of  clasp  material  of  2(5  gauge.  The  end  is 
bent  to  fit  around  the  wire  attached  to  the  crown,  and  the  clasp  then 
bent  to  follow  the  circumference  of  the  crown  as  far  as  the  mesio-pal- 
atal  angle.  This  end  of  the  clasp  is  then  bent  in  similar  fashion,  and  a 
piece  of  iridio-platinum  wire  slipped  bet\veen  the  clasp  aiid  the  crown. 
The  tiniest  drop  of  solder  is  now  fused  to  hold  the  wire  and  crown  to- 

FiG.  886 


gether,  and  the  clasp  is  then  removed  and  the  wire  firmly  attached  to 
the  crow^n  with  more  solder.  The  clasp  thus  fitted  is  then  stiffened  by 
flowing  solder  over  its  outer  surfaces.  The  clasps  are  attached  to  the 
plate  in  the  usual  manner.  Fig.  885  shows  an  artificial  palate  with  gold 
crowns  in  place  and  (Fig.  880;  a  plate  with  clasps  of  this  nature.  The 
plate  in  this  illustration  carries  a  Kingsley  velum,  but  the  plate  for  an  ob- 
turator would  be  essentially  the  same  except  that  its  posterior  edge  would 
be  angular  to  fit  into  the  palatal  surface  of  the  hard  rubber  obturator 
(see  Figs.  887  and  889),  which  prevents  lateral  moxement  of  the  obturator 
when  bolted  to  the  carrying  plate. 

The  metal  plate  and  clasps  having  been  accurately  fitted  to  the  mouth, 
a  loop  of  copper  wire  is  soldered  temporarily  to  the  upper  side  of  the 
plate  (with  soft  solder)  and  extended  backward  about  two-thirds  the 
length  of  the  fissure.  The  object  of  this  is  to  hold  a  mass  of  impression 
material  which  is  to  be  used  for  forming  the  model  of  the  obturator. 
This  mass  of  impression  material  is  wrapped  about  the  wire  loop  and 


THE  CONSTRUCTION  OF  AN  OBTURATnR. 


827 


then  fashioiieil  into  the  general  shape  of  the  fissure,  wlien  it  is  hardened 
in  cold  water.  A  trial  in  the  mouth  will  indicate  wherein  it  must  be 
altered  by  trimming  with  a  sharp  knife.  The  mass  having  been 
brought  to  an  approximation  of  the  proper  form  after  this  manner,  it  is 
then  slightly  softened  in  warm  water  and  again  placed  in  the  mouth, 
whereupon  the  patient  is  tlirected  to  swallow  several  times.  This  com- 
pels the  levator  and  constrictor  muscles  to  close  upon  the  softened  mass 
and  mold  it  into  such  shape  as  will  be  required  to  enable  the  patient  to 
completely  close  the  opening  to  the  nares.  Upon  removal  the  mass  will 
have  assumed  an  irregular  shape,  which  now  must  be  altered  to  fur- 
nish the  final  model  of  the  obturator.  The  palatal  surface  is  trimmed 
into  a  continuous  flat  surface,  so  that  in  connection  with  the  plate 
the  arch  of  the  vault  is  completed  and  the  gap  in  the  back  of  the  mouth 
bridged  over.  The  upper  surface  is  similarly  cut  av/ay,  and  is  usually 
best  formed  with  a  depression  curved  laterally,  experience  having 
taught  that  such  a  form  is  best  adapted  for  the  obliteration  of  the  nasal 
quality  of  the  voice.  Thus  the  sides  and  the  posterior  end  are  left 
undisturbed  as  thev  were  molded  bv  the  action  of  the  muscles. 


Fig.  SS7 


Fig.  8SS 


Fig.  889 


It  must  be  remembered  that  no  matter  how  yielding  the  mass  may 
have  been,  it  is  also  sufiiciently  resistant  to  have  prevented  the  muscles 
from  closing  to  their  utmost  limits.  It  is  therefore  necessary  to  trim 
these  surfaces  so  as  to  still  further  reduce  the  size  of  the  bulb,  especially 
at  the  posterior  end,  where  the  ridge  of  the  pharynx  is  expected  to 
touch  it.  In  the  region  of  the  uvulse  the  side  must  be  trimmed  away 
so  that  they  may  close  tinder  the  obturator,  and  to  this  end  that  part  of 
the  bulb  may  be  narrowed  at  the  lower  and  widened  at  the  upper  side, 
thus  producing  inclined  planes  against  which  the  levators  \\\\\  play  and 
be  in  contact  at  all  times  during  their  contractions.  In  the  region  of 
the  u\ailse  the  bidb  may  be  cut  away  on  a  line  with  the  bases  of  the 
miilse,  so  that  the  surface  produced  "^dll  be  a  plane  which  if  extended 
by  an  imaginary  line  w^ould  reach  the  incisive  edges  of  the  anterior 
teeth. 


828  PALATAL   MECHANISM. 

Figs.  887-889  are  introduced  to  show  the  great  variations  in  the 
forms  of  the  bulbs,  the  size  and  shape  being  dependent  upon  the  pecu- 
Uarities  of  the  fissures  and  activity  of  the  throat  muscles.  In  Figs. 
887  and  889,  a  indicates  the  flat  surface  where,  as  has  been  described, 
the  bulb  is  cut  away  near  the  bases  of  the  uvulae,  while  b,  b  show  the 
slanting  sides  against  which  the  levators  play.  Fig.  888  shows  the 
nasal  surface  of  a  large  obturator,  and  along  the  centre  is  seen  the  de- 
pression, wliich,  experience  has  taught,  is  serviceable  in  many  cases  in 
correcting  the  nasal  quality  of  the  voice  usually  present.  Upon  the 
upper  surface  the  depression  alluded  to  is  seen  at  c,  but  it  must  be 
borne  in  mind  that  this  is  not  always  a  necessity,  being  less  so  in  small 
obturators  (as  in  Figs.  887  and  889)  than  in  large. 

The  model  having  been  brought  to  this  point,  plaster  is  mixed  as  for 
an  impression,  and  a  little  placed  upon  the  upper  side  of  the  plate,  ex- 
tended from  where  the  impression  material  ends  sufficiently  forward  to 
reach  the  anterior  end  of  the  fissure  when  placed  in  the  mouth.  The 
plate,  with  plaster  upon  it,  is  then  quickly  carried  into  place,  and  upon 
removal  the  plaster  will  have  taken  an  impression  of  the  forward  part 
of  the  cleft.  It  is  cut  away  to  a  level  with  the  upper  side  of  the  im- 
pression material,  and  with  it  completes  the  model  of  the  obturator, 
which  must  now  be  reproduced  in  hard  rubber. 

Plaster  molds  are  next  made  in  which  to  reproduce  the  bulb  in  hard 
rubber,  and  when  flasked  and  ready  for  packing  the  bulb  is  made  as 
follows:  Patterns  of  the  upper  and  under  surfaces  are  cut  from  thick 
tin-foil,  and  a  single  pattern  to  extend  around  the  sides  and  end.  These 
are  similarly  cut  from  sheet  rubber,  and  are  united  in  the  general  form 
of  the  bulb  by  placing  the  edges  together  and  pinching  them  fast  with 
a  pair  of  tweezers.  Before  finally  closing,  water  should  be  introduced 
filling  the  bulb  about  three-quarters  full,  great  care  being  observed 
lest  the  edges  of  the  rubber  should  })ecome  wet,  which  would  prevent 
perfect  union  and  allow  an  escape  of  steam  during  vulcanization,  the 
result  being  a  collap.se  of  the  bulb.  If  these  steps  are  accurately  taken 
and  the  flask  tightly  closed,  the  bulb  will  be  thoroughly  well  filled  out 
and  will  be  a  perfect  reproduction  of  the  model. 

The  bulb  is  next  to  be  fitted  to  the  plate,  the  proper  position  being 
determined  by  models  which  were  taken  while  the  plate  and  wax  (im- 
pression material)  model  were  united.  A  hole  is  then  drilled  through 
the  bulb  and  plate,  through  which  an  iridio-platinum  bar  is  passed  and 
soldered  to  the  plate,  the  opposite  end  l)eing  screw  cut  and  supplied 
with  a  nut.  The  hole  drilled  through  the  bulli  for  the  passage  of  the 
bar  also  serves  for  the  removal  of  the  water  used  in  \Tilcanizing.  The 
surface  of  the  plate  over  which  the  bulb  is  to  lie  is  smeared  with  gutta- 
percha, the  bulb  .slipped  over  the  bar,  and  the  nut  turned  down  until  it 
impinges.  Then  by  warming  the  plate  over  a  Bunsen  burner  the  gutta- 
percha is  softened  and  the  nut  screwed  dov,'n,  dri\ing  the  obturator 
tight  against  the  plate,  the  gutta-percha  ser\nng  to  form  a  water-tight 
joint.  The  plate  and  bulb  are  then  polished  and  are  ready  for  the 
patient. 


DR.  CASE'S  VELUM  OBTURATOR. 


829 


DR.  CASE'S  VELUM  OBTURATOR. 

Dr.  Case  describes  his  method  as  follows: 

The  model  of  the  body  of  the  palate,  as  shown  inFicj.890,  is  formed 
first,  and  then  inserted  in  the  mouth  for  trial.  This  can  usually  be 
accomplished  with  the  hand  alone,  by  passing  it  back  of  its  proper 
position  and  then  bringing  it  forward.  It  should  be  done  quickly  and 
easily  r  or  contraction  of  the  muscles  will  prevent  its  accomplishment. 

Fig.  890 


At  this  time  the  lateral  nasal  extensions  of  the  model  should  be  abridged 
to  facihtate  introduction.  They  can  be  added  at  the  time  of  invest- 
ment and  still  further  extended,  as  can  other  parts,  by  scraping  the 
metal  casts. 


Fig      891 


Fig.     892 


The  surface  of  the  pharyngeal  wall  in  the  contracted  position  of  its 
muscles,  which  represents  the  surface  that  is  ultimately  to  close  around 
and  press  against  the  peripheral  border  of  the  artificial  veil,  is  obtained 
with  a  loop  of  No.  22  soft  copper  wire,  the  free  ends  of  which  pass  into 
tubes  imbedded  in  the  upper  surface  of  che  model,  as  shown  in  Fig.  891. 

The  loop  is  dravvm  out  and  bent  to  about  the  proper  size  and  shape, 
and  the  model  then  inserted  in  the  mouth  for  correction.     This  is  re- 


830  /'- 1  LA  T.  1 L    MJy  11. 1  MS.V. 

peated,  bending,  enlarging  or  contracting,  etc.,  until  the  wire  is  seen  to 
rest  along  surfaces  that  are  best  adapted  to  unite  in  their  action  with  the 
artificial  veil  for  the  ultimate  closure  of  the  naso-pharyngeal  opening. 

The  posterior  line  of  wire  should  rest  just  in  front  of  or  slightly 
above  the  greatest  contracted  extension  of  the  superior  pharyngeal 
muscle.  The  surrounding  muscles  can  be  made  to  contract  by  a  slight 
titillation  of  the  surface,  and  what  is  of  the  greatest  advantage — the 
pharyngeal  walls  above  and  below  the  wire  can  be  readily  seen  and 
studied  in  their  action  through  the  open  loop. 

The  action  of  the  muscles  alone,  springing  forward  against  the  pli- 
able wire  loop,  pressing  it  back  into  it  sockets,  or  bending  it  to  fit  their 
surfaces,  will  frequently  cause  it  to  mark  the  desired  peripheral  outline 
of  the  artificial  velum. 

As  the  loop  turns  forward  to  pass  beneath  the  openings  of  the  Eus- 
tachian tubes,  the  pharyngeal  surfaces  will  often  be  found  corrugated 
and  thrown  into  irregular  folds,  so  that  in  finding  the  smoother  path 
across  these  ridges  to  prevent  the  escape  of  air  at  the  borfler  of  the  veil 
through  the  sulci  it  may  be  found  desirable  to  raise  or  lower  the  wire 
upon  one  side  more  than  the  other.  Forward  of  this  it  soon  comes  in 
contact  with  the  upper  surfaces  of  the  palatal  muscles  as  it  enters  the 
posterior  nares. 

After  fitting  the  wire,  to  mark  the  desired  outlines  of  the  veil,  the 
roll  of  compound  which  is  to  form  the  model  of  the  ])order  of  the  veil 
may  now  be  attached  to  the  loop,  following  the  outline  of  its  peripheral 
surface,  and  finally  adjusted  to  the  mouth  to  correct  imperfections. 

Fig.  892  shows  difi:'erent  views  of  a  model  and  completed  palate. 


THE   AUTHORS   VELUM-OBTURATOR. 

An  analysis  of  the  following  description  of  the  construction  of  my  own 
"velum-obturator"  will  disclose  that  it  is  exactly  what  its  name  implies, 
and  that  the  method  of  producing  it  is  but  a  combination  of  the  technique 
already  described  for  soft  rubber  vela,  and  for  hard  rubber  obturators. 
In  obtaining  a  wax  model  for  the  hard  rubber  obturator,  it  will  be  re- 
called that  we  first  made  the  metal  carrying  plate,  soldered  a  loop  of 
copper  wire  temporarily  to  the  upper  surface  thereof,  molded  composition 
about  this  wire  loop  and  obtained  an  impression  of  the  pharyngeal  region 
by  introducing  this  into  the  mouth  with  the  composition  soft,  and  then 
having  the  patient  swallow.  (See  pages  826,  827.)  This  compound 
impression  was  then  itself  used  as  the  model  for  the  hard  rubber  obtura- 
tor, with  certain  alteration  in  shape,  which  have  been  already  described. 
In  constructing  a  soft-rubber  velum-obturator  the  technique  difl'ers 
slightly,  as  it  is  advisable  to  produce  a  plaster  model  of  the  parts:  one 
which,'  as  already  insisted  upon,  will  show  the  anterior  position  of  the 
mouth  at  rest,  and  the  posterior  or  pharyngeal  region  closed. 

In  the  first  case  treated  by  me,  after  obtaining  the  plaster  model  in 
the  usual  manner,  I  then  fashioned  a  trial  plate  of  gutta  percha,  using 
two  thicknesses  to  afford  greater  stability.     Between  the  two  layers,  I 


THE  AUTHOR'S   VELUM-OBTURATOR. 


831 


placed  the  ends  of  a  copper  wire  loop,  this  loop  entending  backward  and 
being  bent  to  follow  the  curve  of  the  palate.  This  gave  me  a  trial  plate 
similar  to  the  metal  plate  used  in  this  part  of  the  technique  of  making  a 
hard  rubber  obturator. 

Fig   893 


It  is  not  absolutely  essential  to  have  this  wire  loop,  but  it  is  an  added 
safeguard  against  dislodgement  of  the  wax  which  is  to  be  used  for  taking 
the  impression  of  the  throat,  and  leaves  the  operator  fairly  certain  that 
the  patient  will  not  swallow  the  mass  of  wax,  an  accident  not  at  all 
impossible. 


Fig.  S94 


In  the  case  under  description,  the  cleft  in  the  palate  was  so  far  back 
that  the  copper  wire  was  also  a  convenience  in  spanning  the  gap  between 
the  posterior  border  of  the  hard  palate  and  the  anterior  border  of  the 
cleft.     (See  Figs.  893  and  894.)     The  wire  loop  was  then  wrapped 


832  PALATAL  MECHANISM. 

with  a  ma.s.s  of  ordinary  beeswax  and  formed  into  a  mass  approximately 
a  little  too  large  for  the  cleft.  This  was  then  softened  in  warm  water, 
introduced  to  place  and  held  in  the  mouth  with  the  forefinger  while  the 
patient  was  instructed  to  swallow  repeatedly.  When  removed,  this 
wax  afi'orded  an  api)roxiniate,  not  an  accurate,  impression  of  the  j)harynx 
when  closed.  It  might  be  accurate,  and  it  might  not,  depending  upon 
the  strength  of  the  parts  to  compress  the  wax  fully.  However,  an  ap- 
proximate impression  is  all  that  is  needed  at  this  stage.  Next  a  con- 
siderable portion  of  the  surface  of  the  wax  is  ciit  away,  and  so  cut  that 
the  surface  is  left  quite  rough.  It  must  also  l;e  trimmed  away  suffi- 
ciently so  that  when  introduced,  and  the  patient  is  allowed  to  swallow, 
he  will  report  that  he  does  not  feel  it. 

This  wax  mass  is  then  covered  with  a  layer  of  creamy,  quick  setting 
plaster  of  Paris,  is  placed  in  the  mouth  and  the  patient  again  asked  to 
swallow  repeatedly.  There  is  no  danger  that  the  plaster  will  drip  down 
the  throat  unless  altogether  too  much  plaster  be  used.  Indeed,  in  hand- 
ling plaster  in  the  mouth  an  excess  should  never  be  introduced.  How- 
ever, as  an  additional  precaution,  the  operator  may  have  at  hand  two 
or  three  swal>s,  made  l^y  wrapping  cotton  aroimd  the  end  of  sticks  of 
orange  wood.  With  these  swabs  dry,  if  any  plaster  should  be  seen  to 
trickle  downward,  it  can  be  quickly  and  deftly  wiped  away. 

Fig.  893  shows  the  trial  j^late  remo\ed  with  the  plaster  impression  of 
the  pharyngeal  opening  which  is  left  by  the  contraction  of  the  muscles. 
This  gutta-percha  plate,  ha^'ing  been  accurately  made  on  the  already  con- 
structed model  is  readily  replaced  thereon,  and  the  impression  of  the 
pharyngeal  region  will  extend  back  beyond  it.  The  plaster  used  in 
taking  this  impression  should  be  slightly  colored  by  adding  paint  powder 
to  the  mixing  water,  or  else  it  should  be  thoroughly  \arnished  with  shellac, 
followed  by  sandarac.  The  trial  plate  carrying  the  impression,  having 
been  placed  on  the  model,  additional  plaster  is  added  to  the  posterior 
part  of  the  model  so  as  to  completely  surround  the  impression.  Later,' 
when  thoroughly  hard  and  the  impression  was  remo^'ed  the  result  was 
the  model  seen  in  Fig.  894,  which  shows  the  hard  and  soft  palatal  regions 
at  rest,  and  the  pharyngeal  muscles  contracted. 

On  this  plaster  model,  a  wax  model  of  the  velum-obturator  is  formed, 
having  secured  which,  metal  molds  are  made  from  the  wax  model  exactly 
as  has  been  described  for  making  a  Kingsley  soft  velum.  The  \elum- 
obturator  made  for  my  first  case  is  seen  in  Fig.  8G7  attached  to  its  metal 
carrying  plate.  In  Fig.  893  it  will  be  observed  that  there  is  a  flat  or  plane 
surface  on  the  top  of  the  plaster  impression.  This,  of  course,  is  not  as  it 
would  be  when  removed  from  the  mouth,  but  it  has  been  so  trimmed,  for 
comparison  with  the  velum-obturator  seen  in  Fig.  891. 

In  the  main  there  may  be  said  to  be  three  classes  of  cleft  palate  cases 
which  may  come  in  for  treatment.  Those  in  which  the  cleft  is  in  the  soft 
palate  only  (Fig.  894);  those  in  which  the  hard  ])alate  is  also  involved 
(Fig.  895);  and  those  resulting  from  failures  of  surgeons  (P'ig.  899.) 

I  am  glad  to  say  that  thus  far  I  have  been  successful  with  my  new- 
instrument  in  all  three  conditions. 


THE  AUTHOR'S  VELUM-OBTURATOR. 


833 


I  have  said  that  the  wax  model  of  the  vekim-obturator  is  made  directly 
on  the  model,  and  then  removed  and  used  in  forming  the  metal  molds  in 
which  the  soft  rubber  is  to  be  vulcanized.  But  sometimes  the  removal 
of  the  wax  model  would  be  impossible  with  the  model  entire.  Such 
a  condition  is  shown  in  Fig.  895,  where  the  plaster  reproductions  of  the 
split  uvula"  would  hinder  the  removal  of  the  wax.  It  is  therefore  advis- 
able to  split  the  model  in  half,  but  at  the  same  time  means  must  be 
provided  for  accurately  reassembling  the  two  halves  of  the  model. 
I,  therefore,  car^'e  a  V-shaped  groove  in  the  under  side  of  the  model,  and 
pour  a  base  or  stand  to  receive  it.     I  saw  the  model  almost  through,  and 

Fig.  895 


then  forcibly  break  it  into  two  parts.  This  is  better  than  sa^nng  it 
entirely  through,  as  the  fractured  edges  \\dll  co-apt  more  closely  when 
reassembled.  Fig.  896  shows  the  model  split  in  tw^o  and  the  base,  and 
Fig.  897  shows  a  side  view  of  the  model  reassembled  and  held  together 
by  the  base  in  which  it  is  set.  This  division  of  the  model  not  only  facili- 
tates the  forming  of  the  wax  model  of  the  velum-obturator,  but  also 
affords  a  guide  for  trimming  away  the  upper  or  nasal  surface,  as  is  seen  in 
Fig.  867,  and  again  in  Fig.  898,  which  is  the  velum-obturator  made  for 
the  case  shown  in  Figs,  895,  896,  and  897.  It  is  not  advisable  that  these 
instruments  should  be  made  too  thick.     The  usual  method  is  to  lea^e  a 

53 


834 


PALATAL  MECHANISM. 

Fia.  896 


good  broad  surface  for  posterior  and  lateral  contact,  and  then  cut  away 
the  plane  to  a  level  with  the  upper  surface  of  the  carrying  plate.    (See  Fig. 


THE  AUTHOR'S   VELUM-OBTURATOR. 


835 


867.)  Having  the  model  divided  enables  the  operator  to  place  the  wax 
model  in  position  in  one-half,  and  thus  study  the  space  which  it  is  desir- 
able to  leave  when  cutting  away  the  upper  surface  of  the  wax. 

In  Fig.  899  we  see  the  model  of  a  case  which  resulted  from  a  surgical 
failure.     The  cleft  in  the  palate  has  been  partly  bridged  with  inelastic 

Fig.  897 


scar  tissue,  the  uvulse  have  been  entirely  destroyed,  and  the  region  of  the 
pharynx  so  mutilated  that  I  almost  despaired  of  accomplishing  anything. 
The  throat  when  at  rest  presented  a  large  uniform  passage  with  smooth 
walls,  but  when  contracted  in  the  act  of  swallowing  the  muscles  all  came 
into  conspicuous  view.  The  model  Fig.  899  is  good  evidence  therefore 
that  it  is  made  from  an  im- 
pression of  the  parts  when 
constricted.  For  this  pa- 
tient I  made  the  velum-ob- 
turator shown  in  Fig.  900. 
I  utilized  the  small  aperture 
in  the  centre  of  the  palate 
as  a  point  at  which  to 
thicken  the  rubber  suffi- 
ciently to  close  the  aperture 

and  at  the  same  time  to  grasp  the  post,  which  is  always  placed  on  the 
upper  side  of  the  metal  carrying  plate,  and  over  which  the  soft  rubber 
part  buttons.  -  We  then  observe  (Fig.  900)  a  stretch  of  rubber  formed 
to  overlay  the  surgical  bridge  in  the  soft  parts;  this  was  made  just 
thick  enough  to  afford  stability,  but  was  further  supported  by  an 
extension  from  the  carrying  plate.     At  the  posterior  part  of  the  illus- 


s-^ii 


PA  LA  TA  L   MKCIIA  NISM. 


tratioii  is  seen  a  bulbous  mass,  which  is  made  to  exactly  conform  to  the 
aperture  left  by  the  closure  of  the  pharynx. 

This  instrument  was  larjjely  experimental,  but  it  is  i)leasant  to  report 
the  result.      The  youn^  man  impnned  so  nmch  that  he  conceived  the 


Fig.  S!)9 


purpose  of  studying  dentistry,  partly  with  the  idea  of  some  day  helping 
others  sufl'ering  with  like  deformity.  When  I  learned  this,  and  that  he 
was  already  at  a  dental  school,  I  cheerfully  presented  him  with  the  metal 
molds,  and  he  now  makes  his  own  duplicates. 


Fig.  900 


There  is  one  advantage  of  this  velum-obturator  which  is  worth  record- 
ing. Being  made  in  larger  masses  than  the  Kingsley  velum  the  soft 
rubber  is  not  so  quickly  destroyed  by  the  fluids  of  the  mouth,  nor  is  it 
distorted  by  curling  up.     It  therefore  requires  renewal  less  frequently. 


INDEX. 


Absorption  of  alveolar  process,  time  for 
complete,  275 
ridge,  hereditary,  780 
Abutment  crowns,  construction  of,  737 
physiological  resistance  of,  733 
preparation  of,  735 
mechanical,  735 
preliminary,  735 
for  removable  bridges,  retaining,  749 

supporting,  757 
strength  of  various  classes  of  teeth 
as,  732 
Accessories  of  molding  bench,  26 
box,  26 
of  plaster  table,  28 
of  soldering  table,  45 
of  work  bench,  23 
Acid  alum  for  pickling,  63 
Adhesion,  389 

description  of,  389 
of  mucous  membrane  complicating 
insertion  of  plate,  278 
Adhesive  wax,  86 
Alkaline  sulphides,  solution  of  vermilion 

by,  in  mouth,  782 
Allen,  Dr.  John,  formula  for  continuous- 
gum  work,  635 
Alloys,  102 

of  aluminum,  138 

annealing  of,  105 

of  bismuth,  154 

as  chemical  compounds,  103 

color  of,  104 

conductivity  of,  105 

of  copper,  149 

decomposition  of,  105 

fusibilitv  of,  105 

of  gold,  119 

influence  of  certain  metals  in,  107 

of  iridium,  134,^135 

of  lead,  159 

malleability,  ductility,  and  tenacity 

of,  104 
of  mercury,  136 
as  mixtures  of  metals,  103 
oxidation  of,  106 
physical  properties  of,  103 
of  platinum,  133 
preparation  of,  108 

according  to  atomic  weights  of 

constituents,  110 
losses  of  metals  in,  109 
use  of  crucible  in,  109 


Alloys,  preparation  of,  use  of  flux  in,  109 
in  prosthetic  dentistry,  91 
of  silver,  128 
sonorousness  of,  105 
specific  gravity  of,  103 
tempering  of,  105 
of  tin,  157 
of  zinc,  153 
Alum  for  pickling,  63 
Alumina,  138 
Aluminum,  138 
alloys  of,  138 
bronze,  139 

dentures,  cases  suitable  for,  281 
occurrence  of,  138 
plate    with    vulcanite    attachments, 

527 
properties  of,  138 
solders  for,  139 
steel,  146 

use  of,  in  removing  oxide  from  molten 
zinc,  311 
for  swaged  metal  plate,  549 
Alveolar  process,  absorption  of,  affecting 
choice  of  artificial  teeth,  414 
effect  of  the  loss  of  the  teeth 

upon,  235 
time  to  allow  for  absorption  of, 
275 
Alveolo-dental  abscess,  treatment  of,  in 

teeth  to  be  crowned,  674 
Amalgam,  102 

results  following  use  of,  for  setting 
crowns,  783 
Amorphous  form  of  metal,  94 
Amputation  of  apex  of  roots  of  teeth  to 

be  crowned,  674 
Annealing,  96 
alloys,  105 
ingot,  42 

plates  in  swaging,  552 
Anterior  triangle  point,  path  of  motion  of, 

377 
Anvil,  swaging,  26 
Arch  outline  of  dentures,  212 
Articulating    paper,    use    of,    in    fitting 
Logan  crown,  710 
plates,  use  of,  in  pouring  impressions 
for  bridge-work,  693 
Articulation  of  consonants,  place  of,  735 
of  teeth,  420 

for  partial  dentures,  456 
Articulators,  335,  353 
Bonwill,  355 
Christensen,  358 

(837) 


838 


INDEX. 


Articulators,  Gritman,  357 
Gysi's,  359 
hinge,  354 
New  Century,  358 
Parfit's,  359 
plain  line,  354 
plaster,  354 
Walker,  357 
Artificial  canine,  use  of,  back  of  natural 
canine,  420 
crowns,  661 

requisites  of,  684 
dentures,  cleansing  of,  784 

hygienic  relations  and  care  of, 

775 
relation  to  facial  movements  of, 

462 
restoration  of  facial  expression 

by,  463 
retention  of,  274 
•securing  data  for  construction  of, 

335 
time  for  insertion  of,  275 
trial  of,  448 
voice  and   speech  relations  of, 

457 
wearing  of,  at  night,  777 
teeth,  anterior,  arrangement  of,  420 
440 
articulation  of,  448 
correct  inclination  of,  423 
curve  of  arch  of,  424 
imitation    of    discoloration 
in,  429 
of  individual  peculiari- 
ties, 428 
of  opaque  white  spots 
in,  429 
insertion  of  gold  filling  in, 

429 
lower,  placing  of,  440 
occlusion  of,  448 
relation  of,  to  profile,  421 

of  speech  to,  421 
relative  positions  of,  424 
support  of  lips  by,  421 
articulation    of,    bearing    upon 

plate  retention,  389 
bicuspid,  articulation  of,  431 
cusps  of,  determination  of, 

436 
grinding  of,  434 
position  of,  437 
selection  of,  417 
setting  of,  436 
bite  of,  selection  of,  415 
examination  of  mouth  prelimi- 
nary to  insertion  of,  271 
mechanical  requirements  of,  414 
molar,  articulation  of,  431 

cusps  of,  determination  of, 

621 
grinding  of,  434 
positions  of,  437 
selection  of,  417 
setting  of,  436 


Artificial  teeth  for  partial  dentures,  selec- 
tion of,  418 
selection  of,  409 

as  to  absorption  of  process, 

414 
color  of,  412 

in     edentulous     cases, 
409,  412 
as  means  of  attachment  to 

base  plate,  414 
for  partial  dentures,  418 
size  and  form  of,  410 
"shut"  of,  selection  of,  415 
surgical  complications  affecting 
insertion  of,  277 
vela,  construction  of,  820 
velum,  789 
Asbestos   soldering   and    melting   block, 
57 
supports,  58 
Ash's  porcelain  furnace,  64 
Assemblage  of  united  crowns,  725 
Atmospheric  pressure,  397 

retention  of  plate  dentures  bv, 
397 
Atomic  weights  of  elements,  91 
Auriferous  minerals,  111 
Autogenous  soldering,  108 
Automatic  blowpipes,  51,  52 
Automaton  blowpipe,  48 
Axes  of  the  teeth,  direction  of,  221 

B 

Babbitt  metal,  150 

Haskell's  formula  for,  312 
Backings,  making  of,  for  swaged  metal 
plates,  620 
for  swaged  metal  plates,  where  teeth 
have  rough  backs,  624 
Bailey's  flash  for  molding,  317 
Balkwill   on   incisive  action  of  anterior 

teeth,  215 
Band  and  pin  crowns,  700 
Base,  choice  of,  279 

effect  of,   upon  artificial  teeth, 
414 
metals,  92 

classes  of,  according  to  affinity 
for  oxj'gen,  92 
to     decomposition     of 
water,  92 
plate,  gold,  280 

\'\ilcanite,  279,  482 

arranging  teeth  on,  486 
finishing  of,  484 

maxillarv     surface    of, 
483 
flasking  of,  482 
packing  of,  484 
vulcanization  of,  484 
wax,  87 
Beaded  plates,  393 

vulcanite,  534 
Bean's  alloy,  157 

interdental  splint,  541 


INDEX. 


839 


Beeswax,  advantages  and  disadvantages 

of,  for  taking  impressions,  283 
Bench  tools,  88 

Bessemer's  process  for  making  steel,  144 
Bicuspid  teeth,  artificial,  articulation  of, 
431 
cusps  of,  determination  of, 

436 
grinding  of,  434 
position  of,  437 
selection  of,  417 
setting  of,  436 
lower,  preparation  of,  for  crowns, 

680 
and  molar,  occlusion  of,  215 
relative   height    of   buccal   and 

lingual  cusps  of,  224 
upper,      preparation      of,      for 
crowns,  680 
Bilious  temperament,  256 
Binary  temperamental  compounds,  table 

of,  260 
"Biscuit"  burning  of  porcelain  teeth,  164 
Bismuth,  154 

action  of  acids  on,  154 
alloys  of,  154 
fusing  point  of,  154 
occurrence  of,  154 
properties  of,  154 
Bite  of  artificial  teeth,  selection  of,  415 
taking  the,  335 

position  of  occlusion  in,  335 
rationale  of  method  of,  336 
selection    of    color    of    artificial 

teeth,  336 
technique  of,  340 
Bite-plates,  337 

contact  of,  importance  of,  343 

judging  of,  343 
for  full  lower  with  upper  denture  in 
place,  351 
upper  wath  lower  natural  teeth. 
350 
grooves  for  fixation  in,  345 
for  lower  jaw,  339 

construction  of,  339 
for     continuous-gum     den- 
tures, 340 
determination  of  length  of, 

343 
for  metal  plates,  340 
for  vulcanite  work,  340 
marking  high-lip  line  upon,  349 

median  line  upon,  349 
material  used  for,  337 
for  partial  dentures,  351 
purpose  of,  337 
requirements  of,  337 
restoration  of  facial  contours  by,  340 
for  temporary  dentures,  351 
trial  of,  340     -, 

Ulsaver's  method,  441 
Wilson's  method,  445 
trimming  of,  340 

uniting  of,  with  plaster  of  Paris,  349 
with  wax,  349 


Bite-plates  for  upper  jaw,  338 

construction  of,  338 

by  Evans'  method,  338 
determination  of  length  of, 

342 
guide  for  position  of   ante- 
rior teeth,  422 
steps  in  formation  of,  339 
of  wax,  objections  to,  337 
Black  on  force  used  in  crushing  food,  232 
on  fungi  as  irritants  under  plate  den- 
tures, 782 
rubber,  use  of,  520 
Blind  abscesses,  treatment  of,  in   teeth 

to  be  crowned,  675 
Blister  steel,  145 
Blowpipe,  automaton,  48 
operation  of,  48 
flame  of,  31 

proportion  of  air  and  gas  in,  32 
for  soldering,  32 
gasoline,  51 
hot  blast,  51 
Knapp's,  39 
Lane's,  50 

advantages  of,  50 
Lee's,  50 
Melotte's,  50 
mouth,  46 
nitrous  oxide,  39 
oxyhydrogen,  39 
regulating  appliances  for,  51 
Bonwill  articulator,  355 
Bonwill's   method   of   grinding   artificial 

teeth,  434 
Borax,  action  of,  in  soldering,  45 
chemistry  of,  45 
fusing  of,  45 
glass,  45 
powdered,  45 
slate,  45 
solution  of,  45 
Box  vulcanite  flask,  505 
Brass,  150-  * 

cast,  151 
formula  for  good  sheet,  151 

wire,  151 
molder's  sand,  319 
molds  for  porcelain  teeth,  172 
Brazier's  solder,  152 
Bridges,  saddle,  759 
Bridge-work,  725 

immovable,  abutments  necessary  in, 

732 
manufacture  of,  737 
occlusion  in,  740 
physiological  aspects  of,  733 
porcelain  crowns  in,  766 
removable,  744 

abutment  pieces  for,  749 
anchorage  in,  744 

advantages  of,  745 
Bonwill  form,  726 

advantages  of,  727 
mechanical  aspects  of, 
728 


840 


INDEX. 


Bridge-work,   removable,    Honwill  form, 
objections  to,  728 
purposes  of,  727 
cementing  of,  763 
facings  for,  backing  of,  738 
grinding  of,  738 
selection  of,  738,  740 
requisites  of,  736 

results  of  excessive  strain  from,  783 
setting  of,  774 

with  breaks  in  the  continuity  of  its 
body,  741 
Britannia  metal,  150,  158 
Bronze  for  porcelain  tooth  molds,  179 
Brophy's  porcelain  furnace,  65 
Brown  on  porcelain  bridge-work,  772 
Brush  for  use  in  molding,  315 

wheels  for  polishing,  83 
Bulb  obturator,  construction  of,  825 
Bulkhead  bridge,  strain  upon,  732 
Bunsen  burner,  48 

flame  of,  31 
Burner  for  gasoline  blowpipe,  54 
for  heating  up,  59 
for  mouth  blowpipe,  48 
for  petroleum  in  crucible  furnace,  37 
Burnisher,  disuse  of,  at  present  for  finish- 
ing, 86 
Burnishing  rim  of  metal  plates,  614 
Byram  on  dental  pja-ometer,  76 


Calaverite,  1 1 1 

Calcined  buckhorn  for  finishing,  85,  86 
Cam-lock  vulcanizer,  508 
Candle,  flame  of,  30 

Canine  eminence,  necessity  for  restoration 
of  contour,  471 
with  bite-plate,  342 
teeth,  joint  between  bicuspids  and  in 
metal  platework,  596 
occlusion  of,  220 
Caoutchouc,  472 

chemistry  of,  473 
composition  of,  473 
former  uses  of,  472 
formula  of,  474 
history  of  use  of,  472 
method  of  obtaining,  473 
physical  properties  of,  472 
preparation  of  crude,  473 
purification  of,  473 
solvents  of,  473 
Cap  crowns,  band  for,  contouring  of,  694 
fitting  of,  690 
cusps  for,  carving  of,  695 

soldering  on,  694 
finishing  of,  695 
measurement  of  root  for,  689 
Capon  on  porcelain  and  platinum  jacket 

crown,  699 
Capsular  ligament,  199 
Carat,  a  measure  of  the  fineness  of  gold, 

121 
Carbon  soldering  cylinder,  58 


Carbon  soldering  support,  58 
Carborundum,  81 

manufacture  of,  81,  82 
furnaces  for,  82 
Carburized  iron,  142,  146 
Case  hardening  of  iron  articles,  145 
Cassiterite,  156 

Cast  for  crown-  and  bridge-work,  693 
gold  crowns,  715 
iron,  142 
making  of,  302 
pouring  of,  305 

removing  imj^ressions  from,  307 
size  of,  306 
trinmiing,  308 
for  vulcanite  work,  308 
Casting  counter-dies,  332 

crowns  directly  on  facings,  718 

dies,  331 

plaster,  use  of  camel's-hair  brush  in, 

28 
process,    availability    of,    in    crown 

work,  715 
rings  for  molding,  315 
"Celluloid"  teeth,  190 

process  of  making  steel,  144 
Chalk  for  polishing  vulcanite  work,  86 
Chamber-piece,  attaching,  567 

soldering  in,  569 
Charcoal,  soldering  support,  35,  56,  57 
advantages  of,  56 
artificial,  56 
ingot  mold  in,  35 
preparation  of,  56 
"Chaser,"     use    of,    in    swaging    metal 
plate,  561 
partial  lower,  581 
m.anner  of  using,  for  swaging  vacuum 
cavity,  562 
Chin,  retruded,  arrangement  of  lips  in,  466 
Christenscn,  articulator  of,  358 

porcelain  furnace  of,  65 
Chrome  steel,  145 
Chronic  alveolo-dental  abscess,  treatment 

of,  in  teeth  to  be  crowned,  675 
Cinnabar,  135 

Clamps  for  attaching  chamber-piece   in 
metal  plate,  568 
rubber  dam,  tempering  of,  148 
solder,  61 
Clasps,  405 

adjustment  of,  to  plate,  587 
applied  to  teeth,  lower  jaw,  406 

upper  jaw,  406 
care  of  plate-bearing,  778 
cleansing  of,  778 
collar,  586 
disintegration  of  tooth  substance  due 

to,  776 
effect  different  in  different  mouths, 
777 
of  kind  of  metal  used  for,  777 
upon  teeth,  776 
form  of,  583 
function  of,  406 

in  several  classes  of  plates,  592 


INDEX. 


841 


Clasps,  gold,  122 

plate  for,  550 
lower  teeth  requiring,  5S6 
material  of,  582 
for  metal  plates,  582 

fitting  to  cast,  584 
partial,  586 

no  pattern  required  for,  584 
proportioning  of  thickness  of  plate 

to  strain  on,  584 
soldering  to  plate,  588 
standard,  586 
stay,  586 

testing  suitability  of  metal  for,  583 
tools  needed  for  fitting,  584 
use  of  half-round  wire  for,  583 
Clay  a  constituent  of  porcelain  teeth,  163 
Cleft  palate,  acquired,  786 

prognosis  of,  787 
causes  of,  786 
complete,  788 
congenital,  788 
impression  of,  810 

Case's  method,  812 
difficulties  of,  810 
"gagging"  in,  810 
procedure  in,  811 
patient's,  education  of,  in  speech, 
794 
Cliche-metal,  155 
Cobalt,  use  of,  in  coloring  porcelain  teeth, 

167 
Coin  gold,  use  of.  in  full  gold  crowns,  690 

silver  used  for  metal  plates,  551 
Coke  soldering  support,  56 
Collar  crowns,  689 

cutting  plate  for,  689 

giving  the  form  of  the  root  to  the 

collar  for,  690 
lap  joints  desirable  for,  689 
measuring  root  for,  689 
method  of  fitting  collars  for,  689 
for  molars,  690 

taking  bite  for,  690 

impressions  for,  690 
requisites  of.  689 
trimming   to   the   gum  outline, 
690 
Color  of  alloys,  104 
Combination  dentures,  526 
Compensating  curve,  testing,  in  artificial 

■teeth,  correctness  of,  438 
Complexion  a  guide  in  selecting  artificial 

teeth,  409 
Compounds  of  metals  and  non-metals,  102 
Compressibility    of    tissues    underhang 

plate  dentiu"es,  393 
Conductivity  of  alloys,  105 

of  electricitv  of  metals,  101 

of  heat  of  metals,  100 

Condylar    part,     determination    of,     in 

taking  the  bite,  365 

Campion's  method,  366 

Christensen's   method, 

366 
Walker's  method,  366 


Condyle    and    fossa,    correspondence    in 
shape  of,  197 
location  of,  in  taking  the  bite,  363 
of  mandible,  197 

difficulties  in  securing  a  distal 

position  of,  345 
position  in  occlusal  relation  of, 
336 
path,  angles  of,  376 

large  registers  for  determining 
slant  of,  369 
Consonants,  243 

factors  determining,  244 
mechanism  of  production  of,  244 
place  of  articulation  of,  243 
relation  of  lingual  surface  of  plate  to, 
459 
Continuous-gum  body,  fusing  point   of, 
649 
dentures,  191,  635 

adaptation  of  base-plate  of,  641 

advantages  of,  636 

Allen's  improvement  of,  635 

body  of,  636 

finishing  of,  emery  for,  86 

formulas  for  porcelain  for,  171 

furnaces  for,  68,  648 

gum  enamel  for,  651 

baking  of,  652 
history  of,  635 

impressions  and  casts  for,  637 
investment  of,  645 
for  lower  jaw,  653 

reinforcement  of  base- 
plate of,  654 
removal  of  wrinkles  in, 

653 
rim  upon,  654 
swaging  of,  653 
metal  used  as  base  for,  636 
objections  to,  636 
for  partial  cases,  654 
lower,  656 

reinforcenient      of 
base-plate,  657 
rim  for,  657 
upper,  654 

clasps  for,  656 
classes  of,  654 
rims  for,  655 
porcelain  body  in,  647 

baking  of,  650 
repair  of,  658 
sections  of,  660 
selection  of  teeth  for,  642 
soldering  of,  646 
strengthening  pieces  for,  640 

soldering  of,  641 
swaging  of,  638 

use  of  counter-die  in,  638 
taking  bite  for,  642 
teeth  used  upon,  642 

arrangement  of,  642 
trial  of  base-plate  for,  642 
use  of,  with  vulcanite  without 
platinum  base-plate,  660 


842 


INDEX. 


Continuous-gum  dentures,  wire  rim  for, 

639 
Contours  established  by  bite-plates,  342 
of   plate,    relation   to   facial   move- 
ments of,  462 
upon  vulcanite  dentures,  536 
Copper,  149 

action  of  acids  on,  149 
alloys  of,  149 
coins,  151 

conductivity  of  electricity,  149 
occurrence  of,  149 
properties  of,  149 
steel,  145 
tenacity  of,  149 
Core-molding,  327 
Cores,  drying  out  of,  328 
material  of,  327 
size  and  shape  of,  328 
Corundum,  80,  138 

in  finishing  metal  dentures,  83 
wheels,  80 

for  grinding  joints,  602 
manufacture  of,  SI 
method  of  use  of,  82 
Counter-dies  for  Babbitt  metal  dies,  159 
casting  of,  332 
definition  of,  310 
metal  used  for,  313 
use  of,  in  swaging,  560 
Countersunk-pin  teeth,  cases  suited  for, 
417 
supporting    abutments    for    re- 
movable bridges,  757 
Crittenden  cement  s}Tinge,  723 
Crowned  teeth,  forms  of,  663 
function  of,  663 
position  of,  662 
stress  upon,  663 
Crowns,  artificial,  classes  of,  661 

availability    of    casting    process    in 

making,  715 
band  and  pin,  700 
banded,  716 
cast  gold,  715 

casting  directly  on  facings,  718 
collar,  689 
de\ntalization  of  pulp  in,  666 

methods  of,  666 
excision  of  crown  of  tooth  for,  670 
full  gold,  690 
gold,  122 
half-cap,  701 
jacket,  695 
pieces  for  brass  mold  for  porcelain 

teeth,  178 
porcelain,  bases  for,  766 
saddles  for,  768 
with  cast  base,  715 
post  and  plate,  685 

impression  for,  687 
model  for  fitting,  686 
p)ost  for,  686 
root  for,  686 

preparation  of,  686 
ready-made,  703 


Crowns,  ready-made,  relations  of,  anat- 
omical, 662 
pathological,  665 
repair  of,  718 
retaining  media  for,  721 
roots  requiring  preparation  of,  666 
mechanical,  676 
therapeutic,  674 
selection  of,  685 
setting  of,  722 
teeth  in,  forms  of,  663 
telescope,  749 
with  porcelain  facings,  717 
Crucibles,  40 

desirable  properties  of,  40 
furnace,  36 

use  of  petroleum  with,  37 
graphite,  40 
Hessian,  40 
materials  of,  40 
steel,  45 
testing  of,  40 
Crystalline  form  of  metals,  94 
Curve  of  occlusal  edges  of  upper  incisors, 
231 
of  Spec,  222 

bearing  of,  upon  movement  of 

mandible,  222 
departures   from,    in   otherwise 

tj-pical  denture,  224 
relation   of,   to   cusp  length   of 
molars  and  bicuspids,  222 
Cusps  for  cap  crowns,  making  of,  695 
soldering  on,  695 
contact,  testing  of,  in  artificial  teeth, 

438 
length  and  overbite,  determination 

of,  in  artificial  dentures,  433 
of  teeth,  use  of,  in  crushing  food,  227 
Custer's  electric  furnace,  68 

method  of  melting  platinum,  40 

of  wiring,  67 
porcelain  furnace,  67 
Cyanide  of  gold  and  potassium  for  elec- 
troplating, 125 


Daly's  gold  lining  for  vulcanite  plate,  532 
Darcet's  fusible  alloj',  156 
Da\ns'  crowns,  704 

grinding  of,  704 
Schwartz  on,  704 
setting  of,  704 
Decomposition  of  allovs,  105 
Deglutition,  233 
Dental  bridge-work,  725 

'laboratory,  17 
De\'italization     of     pulp     for     artificial 

crowns,  666 
Die  and  counter-die,  separation  of,  333 
correcting  defects  in  hot,  331 
definition  of,  310 
of  low-fusing  alloys,  333 
metals  used  for,  32,  311 
requisites  of,  311 


INDEX. 


843 


Die  for  partial  cases,  ronioval  of  teeth 

before  swaj^iiif;-,  572 
Diet,  articles  of  human,  231 

force  used  in  crushing,  232 
Digestion,  effect  of  loss  of  tcetli  on,  235 
Discoloration  of   the   teeth  imitated    in 

artificial  ones,  429 
Distal  position  of  mandible  in  taking  the 

bite,  measures  inducing,  348 
Donliam  vulcanite  flask,  504 
Double  plate,  use  of,  for  swaged  metallic 
plates,  555 
vulcanization   method   in   vulcanite 
work,  second  vulcanization  in,  493 
Dovetailed  key  and  shoe  attachment  for 

removable  bridges,  753 
Downie  crown,  cap  for,  701 

porcelain  furnace,  64 
Draw  plate,  42,  44 

oiling  of,  42 
for  wire,  42,  44 
"Drawing   and    construction   of   human 
figure,"  64 
wire,  42,  44 
Ductility  of  alloys,  104 
of  metal,  95 

effect  of  alloying  on,  95 
of  temperature  on,  96 
Dutch  metal,  151 


Edge-to-edge  bite  of  natural  teeth,  270 
occlusion  of  artificial  teeth  with  natu- 
ral ones,  453 
Edson  vulcanite  flask,  505 

vulcanizer,  508 
Elasticity  of  metals,  97 
Electric  furnaces,  construction  of,  69 

attachment  of  terminals,  74 
case,  71 

finding  break  in,  75 
muffle,  72 
wiring,  72 
Custer's,  68 

practical  working  of,  68 
Hammond's,  69 
Mitchell's,  69 
Pelton's,  69 
porcelain,  66 

advantages  of,  67 
"burning-out"  of,  67 
current  adapted  to,  67 
principle  of,  67 
lathe,  79 
Electro-deposition  of  gold,  125 

of  silver,  129 
Elements,  atomic  weight  of,  91 

table  of,  91 
Emery     for     finishing     continuous-gum 

work,  86 
Enamels,  161 

for  porcelain  teeth,  167 
English  double-acting  foot-bellows,  49 

tube  teeth,  191 
Euphorbiacese  a  source  of  caoutchouc,  472 


p]xcavators,  tempering  of,  148 
Kxi)ansibility  of  metals,  table  of,  100 
Expression,  facial,  250 

muscles  of,  247 
Extension  bridges,  743 
External  lateral  ligament,  202 

pterygoid  muscles,   complication   of 
bite-taking  by,  346 
Extraction  or  retention  of  natural  teeth, 
273 
of  teeth,  time  to  elapse  before  insert- 
ing plate  after,  275 


Face,  contour  of,  changes  of,  due  to  loss 
of  teeth,  251 
expression  movements  of,  246 
external  appearance  of,   a  guide  in 

bite-taking,  342 
ideal  contours  of,  464 
median  line  of,  position  of  anterior 

artificial  teeth  respecting,  422 
skin  of,  effect  of  old  age  upon,  252 
Facial  contour,  restoration  of,  with  bite- 
plates,  342 
testing  of,  by  trying  in  artificial 
dentures,  449 
expression,  250 

data  for  restoration  of,  464 

by  dentures,  463 
mechanism  of,  247 
Feldspar,  chemistry  of,  162 
derivation  of,  162 
preparation  of,  for  porcelain  teeth, 

162 
properties  given  porcelain  teeth  bv, 
162 
Felt  wheels  for  polishing,  83 
Files  for  vulcanite  work,  519 
Finishing  die,  use  of,  in  swaging,  564 
metal  plate,  83 
powders,  85 

swaged  metallic  plates  after  solder- 
ing, 627 
vulcanite  plate,  83 
Fitting  of  clasps,  584 

when  plate  is  tried  in  mouth,  591 
collar  of  crown  to  cast,  694 
metal  plate  to  cast,  565 
model    in    undercut    case,    securing 

mold  by,  325 
teeth  for  swaged  metal  plates,  595, 

596 
upon  a  metal  plate  to  an  upper  or 
lower  denture,  599 
Flame,  30 

analogies  of,  30,  31 
blowpipe,  31 
Bunsen,  31 
candle,  30,  31 
carbon  monoxide,  30 
chemistry  of,  30 
cones  of,  30,  31 
hydrogen,  30 
luminosity  of,  32 


844 


INDEX. 


Flame,  misuse  of,  in  soldering,  32 
oxidizing,  32 

proportion  of  air  and  gas  in,  32 
reducing,  31 
simple,  30 
Flask,  Bailey's,  317 

drying  out  and  heating  up,  71S 
Hawes',  319 
Lewis',  319 
for  molding,  315 
Pearsall,  for  use  in  molding,  319 
presses  for  vulcanite  work,  506 
separation  of,  491 

tongs  for  use  in  vulcanite  work,  518 
for  vulcanite  work,  490,  503 
Flasking  vulcanite  base-plate,  482 
work,  499 

repairing  of,  540 
w'axed  up  case  in  vulcanite  work,  490 
Fletcher  foot-blower,  49 

furnace  for  melting  lead  and  zinc,  33 
ingot  mold  and  blowpipe  combined. 
35,36 
Flexible  rims  for  vulcanite  dentures,  538 
Flue  for  acid  fumes,  63 
Flux,  borax  as,  45 

action  of,  45 
for  reducing  fusing   point    of   tooth 

enamels,   170 
used  in  soldering  aluminum.  140 
Fluxed  wax,  87 
Food,  deglutition  of,  233 

force  used  in  crushing,  232 
Foot-bellows  for  blowpipe,  49 
Foot-blower,  36,  38 
operation  of,  36 
Forging  metals,  97 
Fossa,  glenoid,  196 
Foundation  plate   used  in  making  brass 

tooth  mold,  174 
Fractured  jaw,  splints  for,  541 

roots,  treatment  of,  before  crowning, 

673 
vulcanite  dentures,  cause  of,  538 
Frits,  161 

burning  of,  167 
color  of  gold,  166 

of  platinum,  166 
preparation  of,  165 
used  in  porcelain  teeth,  165 
of  W.  R.  Hall,  165 
of  Wildman,  166 
Frontonasal  column  of  fixed  base,  193 
Full  lower  bite-plate,  construction  of,  339 
swaged  metal  plate,  use  of  two 
laminse  for,  .558 
upper  bite-plate,  construction  of,  338 
Fume  closet,  63 
Fungi   cause   of    irritation    under   plate 

dentures,  782 
Furnaces,  continuous-gum,  68 
crucible,  36 

Fletcher,  -36 

operation  of,  36 
gasoline  generator  with,  36 
electric,  68 


Furnaces,  Fletcher's,  33 

for  fusing  platinum,  131 
injector,  38 
porcelain,  63 
Fusible  alloys,  154 

metal  dies  and  counter-dies,  333 

plates    with    vulcanite    attach- 
ments, 527 
use    of,    in    repairing    vulcanite 
dentures,  540 
Fusibility  of  metals,  97 

effect  of  alloying  ujjon,  97 
Fusing  point  of  alloys,  105 

of  metals,  table  of,  97 
of  porcelain,  75 

G 

Galvanized  iron,  153 

Garhart's  p>Tom.eter,  76 

Garret.son's  method  in  taking  the  bite,  348 

Gas-carbon  furnace,  Fletcher's,  33 

Gasoline  blowpipe,  51 

generator  for,  51 
operation  of,  52,  53 
Bunsen  burner,  56 
Gauge  plate,  42,  43 
Gear's  shaded  rubber  facing  for  vulcanite 

dentures,  .534 
German  silver,  151 
Gingivitis,  272 
Glenoid  fossa,  196 

relation  of,  to  curve  of  Spec,  223 
variations  in  shape  of,  197 
Glycerine,  use  of,  with  marble  dust  for 

molding,  320 
Gold,  110 

ability  to  weld  cold,  ]  18 
alloys  of,  119 
colored,  120 
with  copper,  119 
rules  for  compounding  and  com 

puting,  123 
with  silver,  119 
used  bv  jewelers,  120 
base-plate,  '280 
carat  of,  121 
cast,  for  crowns,  715 
chemically  pure,  115 

precipitating  in,  116 
l)reparation  of,  115 
clasp,  122 

upon  vulcanite  dentures,  522 
composition  of  native.  111 
for  crowns,  122,  715 
cyanide  of,  125 
distribution  of.  111 

in  alluvial  deposits.  111 
in  mineral  veins.  111 
elect rodeposit ion  of,  125 
by  immersion,  125 
b}'  a  separate  current,  125 
fillings,    imitation    of,    in    artificial 
teeth,  430 
insertion  of,  in  anterior  artificial 
teeth,  429 


INDEX. 


845 


Gold,  fusing  point  of,  lis 
minerals  coutainin^.  111 
mold  for,  41 
mosaic,  151 
occurrence  of,  110 
native,  110 
nuggets,  110 
parting  of,  113 
plate  for  clasps,  550 
formulas  for,  122 
making  of,   121 

refitting  of,  with  vulcanite,  531 
used  for  swaged  metal  plate,  549 
plating,  125 
properties  of,  ITS 
refining  of,  112 

quartation  process  of,  113 
roasting  process  of,  112 
solders,  123 

used  by  jewelers,  120 
specific  gravity  of,  118 
sponge,  117 
standard,  119 
tests  for,  in  solution,  125 
transparency  of,  93 
use  of,  for  metal  plate,  549 
Graphite  crucibles,  40 
Gravers,  use  of,  in  finishing  metal  plates, 

627 
Gravity  as  a  means  of  retention  of  lower 

dentures,  402 
Grinding  lathe,  76 

and    polishing  teeth    in    vulcanite 
work,  501 
Gritman,  articulator  of,  357 

mounting  casts  on,  with  Snow 
face-bow,  364 
Gum  enamel  for  continuous-gum  work, 
651 
frit,  168 
section  teeth,  185 

use  of,  in  vulcanite  work, 
519 
teeth,  indications  for,  418 

upon  metal  plates,  599 
grinding    joints    in,    for    metal 

plate  work,  597 
mounting  upon  metal  plates  in, 

600 
for  partial  cases,  420 
selection  of,  418 
tragacanth,  use  of,  in  porcelain  teeth, 
164 
Gums,  morbid  conditions  of,  272 
recession  of,  imitation  of,  428 
in  old  age,  266 
Gunning's  interdental  splint,  541 
Gutta-percha  for  taking  impressions,  285 
Gysi's  articulator,  359 

measuring  instruments,  369 

H 

Half-cap  crown,  701 
Half-round  wire  as  rim  for  metal  plate, 
607 


Hall,  formulas  for  enamels  of,  168 
Hanuners,  swaging,  27 
Hammond   "droj)  bottom"   electric;  fur- 
nace, 69 
Hard-rubber  obturator,  825 
Harveyized  steel,  145 
Haskell  on  vacuum  chambers,  398 
Haskell's  Babbitt  metal,  312 
Hawes'  flask  for  molding,  319 

use  of,  in  undercut  cases,  326 
Head,  on  force  used  in  crushing  food,  232 
Hessian  crucibles,  40 
High  lip-line,  349 
Hinge  articulator,  354 
Hodgen  on  electric  furnace,  69 
Hodgen's  furnace,  muffle  for,  72 

fusible  alloy,  155 
Hollingsworth's    system  of    crown-  and 

bridge-work,  713 
Hollow  bulb  obturator,  828 
Horn  mallet,  use  of,  in  swaging,  559,  560 
Hot-blast  blowpipe,  51 
Huey  on  use  of  porcelain  to  attach  cusps 

to  cap  crowns,  698 
Human  dental  mechanism,  functions  of, 
192 
as    modified    by    tempera- 
ment, age,  and  use,  255 
Hunter    formulas    for     continuous-gum 

work,  171 
Hydrogen  sulphide,  relation  of,  to  \'xilcan- 

ization,  480 
H.ygiene  of  bridge-work,  782 
Hygienic  relations  and  care  of  artificial 

dentures,  775 
Hyperemia  of   oral   mucous   membrane, 
272 
treatment  of,  272 
Hypertrophied   gum,    removal   of,    from 

about  teeth  to  be  crowned,  676 


Impression,  classes  of,  289 
of  cleft  palate,  810 
full  lower,  in  plaster,  294 

upper,  in  plaster,  290 
material,  selection  of,  282 
in  plaster  of  Paris,  286 

assembling  of,  302 
mixing  plaster  for,  286 
for  partial  dentures,  assem- 
blage of,  297 
lower  dentm-es,  300 
preparation  of,  for  pouring 

cast,  302 
removal  of,  293 
remo\ang  from  casts,  307 
taking,  282 
trays,  287 

addition  of  wax  to,  288 
alteration  of,  297 

for  edentulous  mouth,  288 
for  full  lower  case,  287 

upper  case,  287 
kinds  of,  288 


846 


INDEX. 


Impression  trays,  kinds  of,  special,  method 
of  making,  2S9 
for  partial  lower  case,  288 

upper  case,  287 
purpose  of,  287 
requirements  of,  287 
size  and  shape  of,  288 
treatment    of,   before   pouring   cast, 
303 
Incision,  contact  of  teeth  in,  230 
Incisor  teeth,  occlusion  of,  214 
Incisors,  loss  of,  effect  upon  consonants 

of,  246 
India  rubber,  472 
Infection  of  pulp,  treatment  of  conditions 

resulting  from,  674 
Inflammation    caused    by    extraction    of 
teeth,  277 
of  mucous  membrane  under  denture, 
treatment  of,  780 
Ingot  molds,  41 

adjustable,  41 
annealing  of,  41 

and  blowjnpe  combined,  35,  36 
in  charcoal  support,  35 
coating  of,  41 
for  gold  and  silver,  41 
heating  of,  41 
iron,  41 
lime,  41 

for  platinum,  41 
soapstone,  41 
for  wire,  42 
splitting  of,  42 
Injector  furnace,  38 

construction  of,  38 
Inlay  attachment  on  abutment  piece  for 

removable  bridges,  753 
Instruments  and  appliances  used  in  vul- 
canite work,  501 
Interarticular  fibro-cartilage,  198 
Interdental     splints,     arrangements     of, 
casts  for,  543 
covering  casts  with  tin-foil  for, 

544 
flasking  of,  545 
packing  rubber  for,  546 
taking  impressions  for,  542 
of  vulcanite,  542 
Internal  lateral  ligament,  202 
Intra-oral  negative  pressure,  205 
Investment  of  continuous-gum  dentures, 
645 
of  swaged  metallic  plates  for  solder- 
ing, 617 
iron  wire  for,  618 
material  for,  617 
preparation      for, 

616 
separating    joints, 
617 
Iridio-platinum,  use  of,  for  base  plate, 

549 
Iridium,  134 

action  of  acids  on,  135 
alloys  of,  134,  135 


Iridium,  occurrence  of,  134 

properties  of,  134 
Iron,  141 

action  of  acids  on,  148 

carbon  combined  with,  142 

cast,  142 

crude,  142 

founder's  sand,  319 

fusing  point  of,  142 

galvanized,  153 

magnetic,  qualities  of,  141 

modifications  of,  142 

occurrence  of,  141 

pig,   142 

properties  of,  141 

scale,   use  of,   in  coloring  porcelain 
teeth,  166 

sink  for  laboratory,  29 

preparation  of,  30 

wrought,  143 
Ivory,  elephant,  use  of,  for  natural  teeth, 
161 

hippopotamus,    use   of,    for   natural 
teeth,  161 

use  of,  for  artificial  teeth,  161 


Jacket  crowns,  695 

band  for,  696 
for  bicuspid,  696 
facing  for,  696 
indications  for,  695 
root  for,  696 
Jaw,  angle  of,  change  in,  during  life,  239 
in  old  age,  239 
distance  between,  affecting  choice  of 

artificial  teeth,  414 
lower,    protruding,    arrangement     of 
artificial  teeth  in,  449 
in  bite-taking,  347 
selection  of  teeth  for,  416 
relation  of,  affecting  choice  of  arti- 
ficial teeth,  414 
to    temporo-mandibular    joint, 
determination  of,  362 
securing  relationship  of,  in  position  of 

occlusion,  336 
upper,   protruding,    arrangement    of 
artificial  teeth  in,  451 
selection  of  teeth  for,   416 
Joints,  making  of,  between  gum  section 
teeth,  602 


Kaolin,  chemistry  of,  163 

l)ropertics  given  porcelain  teeth  by, 
162 
Kingsbury's  alloy,  157 
Kingsley  velum,  790 

Ottolengui's  modification  of,  808, 
830 
Kirk  on  action  of  alkaline  sulphides  of 
sajiva  upon  vermilion,  782 
dentimeter,  use  of,  689 
Knapp's  blowpipe,  39 


INDEX. 


847 


Laboratory,  heat  in,  30 

appliiinccs  for  production  of,  30 
sources  of,  30 
iron  sink  for,  29 
mechanical,  17 

equipment  of,  17 
furniture  for,  17 
room  for,  17 
size  of,  17 
Ladles  for  fusible  metal,  32 

for  zinc  and  lead,  33,  312 
Land  crowns,  707 
Land's  porcelain  furnaces,  64 
Lane's  blowpipe,  50 
Language,  243 
Larynx,  242 
Lathes,  76 

electric,  79 
head,  77 

chucks  for,  77 
driving  wheel  for,  77 
table,  77 
Lead,  158 

action  of  acids  on,  158 

of  water  on,  159 
alloys  of,  159 
for  counter-dies,  313 

advantages  of,  313 
lack  of  tenacity  of,  158 
occurrence  of,  158 
properties  of,  158 
uses  of,  in  dentistry,  158 
Le  Cron's  nitrous  oxide  blowpipe,  641 

pyrometer,  75,  649 
Lee's  blowpipe,  50 

Leverage  upon  artificial  plate  denture,  394 
Lewis  case  heater,  59 

cross-bar  vrdcanizer,  508 
flask  for  use  in  molding,  319 
Ligament,  capsular,  199 
external  lateral,  202 
internal  lateral,  202 
spheno-maxillary,  202 
stylo-maxillary,  203 
of  temporo-mandibular  joint,  199 
Lingual   conformation  of  artificial   den- 
tures, relation  of,  to  speech,  458 
Lips,  effect  of  loss  of  teeth  upon,  251 
ideal  lines  of,  464 

proper  form  of,  as  restored  by  bite- 
plates,  343    . 
relation  of,  to  forehead,  466 
upper,  proper  form  of,  469 
Liquid  silex,  use  of,  in  vulcanite  work,  483 
Logan  crowns,  708 

bending  pin  of,  708 
enlarging  canals  for,  708 
fitting  of,  708 

Gordon    White's    method, 

710 
Kirk's  method,  710 
heating  of,  711 
setting  of,  708 
with  bands,  711 


Logan     crowns    with    bands,    Hf)l lings- 
worth's  method  of  mounting,  712 
Long  bite  teeth,  misuse  of,  415 
Low-fusing  dies  and  counter-dies,  333 
Lymphatic  temperament,  258 

M 

Malleability  of  alloys,  104 
of  metals,  94 

effect  of  temperature  on,  96 
Mandible,  depression  of,  205 
elevation  of,  207 
movements  of,  205 

combinations  of,  211 
lateral,  209 
protrusion  of,  208 

arrangement  of  lips  in,  466 
retraction  of,  208 
Mandibular  condyle,  197 
Manganese  steel,  145 
Marble  dust  for  molding,  319 
Mastication,  231 

coordinating  mechanism  of,  233 
effect  of  loss  of  teeth  on,  234 
function  of  molar  and  bicuspid  teeth 
in,  231 
of  mucin  in,  233 
of  rugaj  in,  233 
of  saliva  in,  233 

of  teeth  as  tactile  organs  in,  233 
of  tongue  in,  233 
movements  of  the  mandible  in,  231 
Masticatory  ability  of  artificial  teeth,  441 
Matthews'  fusible  alloy,  155 
Mechanical  aspects  of  bridge-work,  728 
laboratory,  17 

equipment  of,  17 
furniture  for,  17 
room  for,  17 
size  of,  17 
requirements  of  artificial  teeth,  414 
Median  line  bite-plates,  349 

guides  to  marking,  349 
importance  of  correctness  of,  in 
fitting  teeth  to  metal  plate, 
595 
Meker's  burner,  31 
Melotte's  blowpipe,  50 

operation  of,  50 
metal,  155 
Mercuric  sulphide,  781 
Mercury,  135 

action  of  acids  on,  136 
alloys  of,  136 
native,  135 
occurrence  of,  135 
ores  of,  135 

presence  of,  in  rubber,  781 
properties  of,  135 
solution  of,  by  nitric  acid,  136 
sulphide  of,  136 
Metallic  plates,  annealing  of  metals  used 
for,  552 
swaged,  549 
taste  on  dentures,  63 


848 


INDEX. 


Metals,  92 
base,  92 
color  of,  94 

coinpounds  of  non-metals  with,   102 
conductivity  of,  100 
ductility  of^  9.") 
elasticity  of,  97 
expansibility  of,  100 
for  dies  and  counter-dies,  32 

melting  of,  32 
forging  of,  97 
forms  of,  amorphous,  94 
crystalline,  94 
for  swaged  metal  plate,  554 
fusibility  of,  97 
fusible,  melting  of,  32 
fusing  point  of,  97 

tabl(>  of,  97 
lustre  of,  94 
malleability  of,  94 
melting  of,  32 
noble,  92 

odor  and  taste  of,  94 
plate,  finishing  of,  83 
rouge  for,  S6 
for  swaged  metallic  plates,  thick- 
ness of,  554 
with  vulcanite  attachments,  rim- 
ming of,  528 
sonorousness  of,  97 
specific  gravity  of,  101 

heat  of,  99 
tenacity  of,  95 

used  in  arts  and  for  medicines  and 
alloying,  92 
for  dies  and  counter-dies,  311 
in  metallic  condition,  92 
in  prosthetic  dentistry,  91 
volatility  of,  98 
welding  of,  97 
work,  tools  for,  S9 
IVIeyer's  jjorcelain  furnace,  64 
Mitchell  electric  furnace,  69 
Model,  preparation  of,  for  molding,  320 
removing,  from  mold,  324 
undercut,  securing  molds  from,  324 
Modelling  compound,  283 

advantages  of,  for  taking  impres- 
sions, 284 
softening  of,  for  taking  impres- 

sioas,  284 
use  of,  283 
Moffitt  formula  for  continuous-gum  work, 

171 
Molars   and   bicuspids,    arrangement    of, 
upon  metal  plates,  598 
effect   upon   consonants  of  loss 
of,  246 
lower,  inclining  forward,  preparation 
of,  for  crowns,  679 
preparation  of,  for  crowns,  ap- 
pliances used  in,  677 
for  full  gold  crown,  676 
teeth,  artificial,  articulation  of,  431 
cusps  of,  determination  of, 
436 


Molars,  teeth,  artificial,  grinding  of,  434 
positions  of,  437 
selection  of,  417 
setting  of,  436 
upper,  preparation  of,  for  crowns,  680 
Molding  bench,  24,  314 

accessories  of,  26 
blocks,  26 
box,  24 

sieve  for,  26 
rationale  of,  310 
sand,  319 

care  of,  320 
preparation  of,  319 
reciuisites  of,  319 
tools  for,  314 
tray,  25 

use  of  painter's  brush  in,  26 
Molds,  brass,  finishing  of,  178 
for  porcelain  teeth,  172 
foundation  plate  for,  175 
fractured,  repairing  of,  325 
ingot,  41 
making,  323 
plaster,  frame  for,  176 
Mosaic  gold,  151 

Mounting  teeth  directly  upon  the  gum,  416 
Mouth  blowpipe,  46 

burner  for,  48 
chamber  in,  47 
collection  of  moisture  in,  47 
danger  from  using,  46 
description  of,  46 
length  of,  47 
material  of,  47 
method  of  using,  46 
mouth-piece  for,  46 
object  of,  46 
operation  of,  46 
of  Thomas  Fletcher,  48 
effect  of  loss  of  teeth  upon,  251 
examination  of,  preliminary  to  in.ser- 

tion  of  artificial  teeth,  271 
expressive  movements  of,  247 
favorable  for  plate  retention,  391 
ideal  contours  of,  464 
unfavorable  for  plate  retention,  391 
with   tissues  of   varying  resistance, 
treatment  of,  395 
Mucous  membrane  of  lips,  displaj'al  of 
equal  amount  of,  470 
support  for  plate  dentures,  386 
Muffle  for  Ilodgen's  furnace,  72 

for  tooth  fiu'nace,  184 
Muscles,  digastric,  205 
of  expression,  247 
action  of,  249 
external  pterygoid,  204 
genio-hyoid,  205 
iiit'>rnal  pterygoid,  203 
mass(>t(T,  203 
omo-hyoid,  205 
operating  mandible,  203 
sterno-hyoid,  205 
temporal,  203 
thyro-hyoid,  205 


INDEX. 


849 


N 

Naoyacjite,  111 

Nasal  (luality  to  voice,  correction  of,  71)3 

Naso-labial  fold,  252 

Natural  teeth,  retention  or  extraction  of, 
273 
use  of,  upon  vulcanite  base,  524 

Nervous  temperament,  258 

New  Century  articulator,  358 

Nickel  steel,  145 

Nitrous  oxide  blowpipe,  39 

melting  of  platinum  with,  38 

Noble  metals,  92 

Non-conductivity  of  vulcanite   cause  of 
irritation,  782 

Non-trans{)arency  i)roperty  of  metal,  93 

Nose,  support  of  corner  of,  by  an  attach- 
ment to  obturator,  793 

Notching  the  cervical  end  of  the  teeth  in 
vulcanite  work,  501 

Niirnberg  gold,  139 

0 

Obturators,  789 

hinge  of,  mode  6f  action  of,  796 
no  value  upon,  797 
valuable  after  surgical  deform- 
ity, 798 
and   velum,    difference   in  mode   of 

action  of,  789 
velum,  789 
Occlusion  of  bicuspids  and  molars,  215 
consciousness  from  teeth  of  position 

of,  345 
of  incisors,  214 

position  of,  in  taking  the  bite,  335 
securing  relationship  of  jaw  in  posi- 
tion of,  336 
of  teeth,  213 
Ohmer  dental  bin,  29 
Onion's  fusible  alloy,  155 
Opaque  white  spots,  imitation  of,  in  arti- 
ficial teeth,  429 
Oreide,  151 
Orthodontic  movement  of  teeth  in  case 

requiring  partial  denture,  419 
Ottolengui,  velum-obturator  of,  830 

construction  of,  830 
Overbite  and  cusp  length,  relation  be- 
tween, 219    _ 
Overhanging  ridge,  securing  mold  from 
model  with,  325 
bv  means  of  cores, 
'  328 
Oxidation  of  alloys,  106 
Oxides,  metallic,  use  of,  in  coloring  por- 
celain teeth,  165 
solution  of,  by  molten  metal,  106 
prevention  of,  with  aluminum, 
107 
with  charcoal,  106 
with  phosphorus,  107 
Oxyhydrogen  blowpipe,  39 
advantages  of,  38 
Taggart's  improvement  for,  39 
54 


Packing  the  mold,  323 

in  vulcanite  work,  492,  500 
Palatal  mechanism,  786 

a  mechanical   device  which  pa- 
tient learns  to  use,  795 
vault,  lack  of  much  change  in,  after 
loss  of  teeth,  237 
Parfit's  articulator,  359 
Parr's  fluxed  wax,  87 
Partial  counter-dies,  use  of,  in  swaging,  560 
dentures,  456 

bite-plates  for,  351 
gold,  281 
vulcanite,  522 
lower     metal    plate,    soldering    two 
lamina)  of,  582 
vulcanite  dentures,  523 
plates,  trying  in  mouth,  604 
upper  metal  plates,  570 
Parting  gold,  113 
Pathological   conditions  incident   to   the 

use  of  artificial  dentures,  775 
Pattern,  use  of,  in  preparing  metal  form 

for  metallic  plate,  556 
Pearsall  flask  for  use  in  molding,  319 
Peeso's,  Frank  W.,  method  of  fitting  por- 
celain crowns,  767 
Pelton  electric  furnace,  69 
Perforated  roots,  treatment  of,  prepara- 
tory to  crowning,  672 
Pericementum,  condition  of,  in  teeth  to 

be  crowned,  664 
Peripheral  contact  of  plate,  accentuation 

of,  392 
Petroleum,  use  of,  with  crucible  furnace, 

37 
Pewter,  160 
Philtrum,  254 

relation  of  plate  dentures  to,  470 
Physical  properties  of  alloys,  103 
Physiological  aspects  of  bridge-work,  733 
Pickling,  61 
pans,  61 

plates  after  annealing,  553 
solutions,  67 

action  of,  45 
Pig  iron,  142 

"Pin"  guard  of  rubber  teeth,  190 
teeth,  countersunk,  191 

advantages  of,  191 
Pinchbeck,  151 
Plain  line  articulator,  354 

necessity   for   correct    con- 
struction of,  355 
teeth,  189 

indications     for,     upon     metal 

plates,  600 
without   gum   restoration   used 
with  A'ulcanite,  518 
Plaster  articulator,  354 

blocks  used  in  making  brass  tooth 
molds,  172 
molds  for  gum  section 
teeth,  175 


850 


INDEX. 


Plaster   cast,   pouring  of,   rcciuisitcs    in, 
305 
casting,  use  of  camel's-hair  brush  in, 

2S 
knife,  309 
model  for  brass  mold  for  porcelain 

teeth,  177 
mold    used    in   making   brass   tooth 

molds,  174 
of  Paris,  29 

advantages  of,   for   taking  im- 
pressions, 285 
care  of,  29 
chemistry  of,  29 
coloring  of,  2So 
container  for,  29 
derivation  of,  29 
impressions  in,  286 
kind  of,  for  casts,  29,  305 

for  impressions,  29,  285 
mixing  of,  29 

for  casts,  305 
phj-sical  properties  of,  29 
preparation  of,  29 
setting  of,  285 
sink,  27 

spatula  and  bowl,  286 
table,  27 

accessories  of,  28 
Plate  bridge  dentures,  747,  763 

for  anterior  teeth,  764 
for  bicuspid  teeth,  765 
for  molar  teeth,  765 
dentures,    articulation    of    artificial 
teeth  on,  388 
correctness  of  plate  outline  in, 

389 
full  lower,  retention  of,  401 

upper  plate  outline  for,  390 
retention  of,  389 
lower,  plate  outline  for,  401 
retention  of,  401 
by  gra\'ity,  402 
mechanical  demand   upon,   386 
partial,  building  up  natural  teeth 
in  mouth  containing,  456 
grinding  teeth  for,  456 
lower,  retention  of,  404 

swaging  of,  580 
plate  outline  for,  403 
reterition  of,  402 

adhesions  in,  402 
atmospheric     pressure 

in,  402 
by  clasps,  405 
.  setting  of  plate  of,  456 
use  of  gum  or  plain  teeth 
in,  456 
rationale  of  method  of  use  of, 

387 
retention  of,  mechanical  aids  to, 
389 
principle  of,  386 
rims  an  aid  in,  387 
support  of,  386 
temporary,  454 


Plate  dentures,  temporarj-,   advantages 
of,  455 
mounting  teeth  for,  455 
plate  contours  in,  455 
upper,  retention  of,  by  adhesion, 
389 
swaging  metal  plate  for,  559 
manufacture  of,  42 
metal,  finishing  of,  83 
rolling  of,  method  of,  42 
teeth,  191 

vulcanite,  finishing  of,  83 
Plate-bending  pliers,  use  of,  preliminary 

to  swaging,  574 
Platine  au  titre,  134 
Platinum,  131 

absorption  of  oxygen  by,  133 
action  of  acids  on,  133 
of  alkalies  on,  133 
alloys  of,  133 
as  a  base  for  continuous-gum  work, 

133 
fusing  of,  131 

furnace  for,  131 
point  of,  132 
melting  of,  40 
mold  for,  41 
not  desirable  to  come  in  contact  with 

natural  teeth,  777 
occurrence  of,  131 
ore  of,  131 
properties  of,  132 
sponge,  preparation  of,  for  tooth  frits, 

166 
use  of,  for  base-plates,  549 
used  in  electric  heating  devices,  133 
Plat  Schick  on  continuous-gum  using  tube 

teeth,  657 
Polishing,  brush  wheels  for,  83 
buffers,  83 
felt  wheels  for,  83 
lathe,  78 
metal  plates,  628 
powders,  85,  86 

carriers  for,  86 
puttv,  157 
wheels,  83 
Pol.N^irene,  union  of  sulphur  with,  in  vul- 
canization, 479 
Porcelain    and    platinum    jacket   crown, 
699 
bridge-work.  772 

platinum  framework  for,  773 
for  continuous-gum  work,  171 
crown,  bases  for,  766 

casting  of,  767 
difficulty  in  fitting,  767 
Peeso's   method   of   fitting, 
767 
bridge- work,  and,  770 

use  of  in,  766 
cap  for,  701 
of  C.  H.  Land,  707 
enlarging  canal  for  pin  of,  684 
saddles  for,  768 
deep,  768 


INDEX. 


851 


Porcelain  crown  with  cast  base,  71") 

cusps   for   molar   and   bicuspid   cap 

•  crowns,  697 
faced    crowns    for    bicusjjids    witli 
vital  pulps,  G9tj 
removal  of,  719 
facing,  crowns  with,  717 

in  gold-barrel  crown,  697 
furnaces,  63 
Ash's,  64 
Brophy's,  65 
Christensen's,  65 
Custer's,  67 
Downie's,  64 
electric,  66 
gasoline,  65 
Land's,  64 
Meyers',  64 
old-fashioned,  64 
of  Turner  Brass  Works,  65 
Vernier's,  64 
fusing  of,  75 

means  of  judging,  75 
teeth,  161 

body  of.  161 
burning  of,  1S3 
carved,  body  of,  165 
classes  of,  185 
constituents  of,  163 
enamels  of,  "base,"  165 

"point,"  165 
finishing  of,  429 
forms  of,  1S8 

manufacture  of,  colors  in,  165 
molding  of,  ISl 
pinless,  ISS 
pins  for,  187 
staining  of,  429 
transparency  of,  161 
Pots  for  melting  lead  and  zinc,  316 
Pouring  plaster  cast,  305 

the  cast  from  an  impression-bite  in 

bridge- work,  691 
the  die,  331 

bubbling  of  zinc  in,  331 
Preparing  molding  sand  for  use,  319 
Price's  p>Tometer,  76 
Profile,  effect  of  loss  of  teeth  upon,  254 

study  of,  464 
Pterygoid  column  of  fixed  base,  193 
"Puddling"  of  molten  iron,  143 
Pulp    devitalization    for     teeth     to     be 
crowned,  666 
infection,  treatment  of,  in  teeth  to 

be  crowned,  674 
removal  of,  in  artificial  crowns,  669 
Pumice  stone  for  finishing,  85 
soldering  support,  56 
Purple  of  Cassius,  168 

preparation     of,    drv    method, 
168 
PjTometer  for  judging  of  porcelain  fus- 
ing, 75 
Garhart's,  76 
Le  Cron's,  75,  649 
Price's,  76 


Q 

QuARTATioN  proccss  of  refining  gold,  113 
Quartz  a  constituent  of  tooth  body,  163 
Queen's  metal,  150 
Quicksilver,  135 

R 

Ready-made  crowns,  703 

Reese's  alloy,  157 

Refining  gold  by  roasting,  112 

with  mercuric  chloride,  113 
with  sulphur  chloride,  113 
Register,  large,  for  determining  slant  of 
condyle  path,  369 
small,  377 
Reinforcing  pieces  for  metal  plates,  pat- 
terns for,  554 
Relief  of  hard  areas  in  mouth  for  purposes 

of  retention,  395 
Removable  bridges,  744 

advantages  of,  727 
cementing,  763 
purposes  of,  727 
Resting  bite,  205 

Re-swaging  metal  plate  to  connect  mis- 
fit, 565 
Retaining     abutments     for     removable 

bridges,  749 
Retention  or  extraction  of  natural  teeth, 
273 
of  partial  dentures,  402 
Retentive  tissues  of  tooth  to  be  crowned, 

condition  of,  664 
Rhodiim:!,  use  of,  in  pjTometer,  76 
Richmond  crown,  700 

enlarging  canal  for  pin  of,  684 
non-irritating  character  of,  783 
"Ridge  lap,"  415 

of  artificial  teeth,   selection  of, 
proper,  415 
Rimming  swaged  metal  plates,  605 

advantages  of,  605 
investing  in,  608 
location  of  rim  in,  606 
soldering  in,  609 
use  of  wire  in,  606 
strips  of  plate  in, 
606 
Rims  for  metal  plates,  half-round  wire 

for,  607 
Rocking,  cause  of,  in  metal  plate,  565 
correction  of,  in  metal  plate,  564 
Rolling  mill,  42,  43 
"Roman  gold"  for  use  in  tooth  staining, 

430 
Root  canals,  filling  of,  for  teeth  to  be 
crowned,  671 
removal  of  pulp  from,  in  teeth 
to  be  cro'mied,  669 
Roots,  fractured,  treatment  of,  for  crown- 
ing, 673 
perforated,  treatment  of,  for  crov^Ti- 
ing,  672 
Rose's  fusible  alloy,  155 


852 


ISDEX. 


Rosin-and-vvax  cement,  S6 
Rotary  air  compressor,  49 
Rouge  for  finishing  metal  work,  86 
Rubber  dam  clamps,  tempering  of,  148 
used  over  die  in  swaging,  500 
slabs  for  swaging,  24 
sore  mouth,  137,  270,  779 

results    improperly    attrib- 
uted to,  7S(J 
treatment  of,  779 
teeth,  190 

"pin"  guard  of,  190 
Rugae,  advantage  of  imitation  upon  den- 
ture of,  461 
method  of  placing  in  vulcanite  plate, 
489 
of    producing    upon    vulcanite 
denture,  462 


"S, "  the  correct  formation  with  denture 

of,  459 
Saddle  bridges,  727,  759 

cementing  of,  763 
finishing  of,  762 
grinding  facings  for,  760 
impression  for,  759 
for  lower  jaw,  759 
swaging  saddle  for,  759 
deep,  for  porcelain  crowns,  768 
for  porcelain  crowns,  768 
Saddle-back  teeth,  191 
Sandarae  varnish,  28 

for   coating  plaster  impression, 

303 
use  of,  28 
Sanguine  temperament,  257 
Scrai)er,  use  of,  in  molding,  316 
Scrapers  for  vulcanite  work,  519 
Seabury  vulcanizer,  509 
Separating  media  for  coating  impression, 

303 
Shear  steel,  145 
Sheet  wax,  preparation  of,  87 
Shellac  for  attaching  teeth  to  metal  plate, 
87 
varnish,  28 

for  coating  plaster  impressions, 

303 
making  of,  28 
use  of,  28 
Shot  swage,  use  of,  with  fusible  metal  dies, 

334 
"Shut"  of  artificial  teeth,  selection  of,  415 
Sieve  for  molding  box,  26,  315 
Silica,  occurrence  of,  163 

preparation  of,  for  porcelain  teeth, 

163 
properties  given  porcelain  teeth  by, 
161 
Silver,  126 

action  of  acids  on,  127 
alloys  of,  120 
base  plate,  281 
electro-deposition  of,  129 


Silver,  malleability  of,  127 

mold  for,  41 

not  desirable  for  clasp  material,  777 

occurrence  of,  126 

ores  of,  126 

plate    with    vulcanite    attachments, 
526 

preparation  of  chemically  pure,  126 

proi)erties  of,  127 

solder,  128 

solvents  of,  127 

standard,  128 

sterling,  128 

tenacity  of,  127 

use  of,  for  swaged  metal  plate,  551 
Sink,  29 

iron,  for  laboratory,  29 

preparation  of,  30 

plaster,  27 
Slides  for  tooth  furnace,  184 
Smith,  D.  D.,  formulas  for  continuous- 
gum  work,  171 
Snow  face-bow,  362 

on   proper   conformation  of   lingual 
surface  of  dentures,  459 
Sodium  p3'roborate,  45 
Soft  rubber  bulb  obturator,  799 

vela,  construction  of,  820 

solder,  159 

tissues  underlying  plate,  treatment 
of,  395 
Solder,  107 

for  aluminum,  140 

brazier's,  107,  152 

formulas  of,  for  use  in  plate  work, 
552 

hard,  107 

preparation  of,  107 

requirements  of,  107 

soft,  107 

spelter,  152 

tongs,  61,  62 

tweezers,  61 

used  for  gold,  123 

in  plate  work,  551 
Soldering,  107 

apparatus  and  accessories,  44 

autogenous,  108 

backings  for  metal  plate  teeth  before 
investing  the  case,  623 

capillary  attraction  in,  44 

clamps,  61 

cleanliness  in,  44 

conditions  of  successful,  44,  107 

contact  in,  44 

continuous-gum  dentures,  640 

cup,  59 

definition  of,  44 

heating-up  case  for,  59 

metal  plates,  preparation  of,  invest- 
ment for,  619 

method  of,  44 

oxidation  in,  44 

pieces  of  bridge-work,  739 

of  platinum  with  gold,  107 

requirements  of,  44 


INDEX. 


853 


Soldering,  results  of  hick  of  contact  in,  44 
rules  for,  in  metal  plates,  026 
supi)orts,  50 

asbestos,  58 
carbon,  58 
charcoal,  56 
coke,  56 
fire-clay,  57 
grajjliite,  57 
pumice-stone,  56 
swaged  metal  plate,  626 

cooling  after,  627 
finishing  after,  627 
heating  up  for,  626 
pickling  after,  627 
table,  45 

accessories  of,  45 
material  of,  45 
wire  rim  on  swaged  metallic  plates, 
615 
Sonorousness  of  alloys,  105 

of  metals,  97 
Specific  gravity  of  alloys,  103 
of  metals,  101 
heat  of  metals,  99 
Speech,  242 

portions  of  artificial  dentures  con- 
cerned with,  457 
Spelter  solder,  152 
Spence's  metal,  313 

Speyer's  lining  for  vulca,nite  plates,  533 
Spiegel-eisen,  144 
Spiral  springs,  629 

for  plate  retention,  400 
hygienic  relations  of,  778 
Splints,  vulcanite,  interdental,  542 
Splitting  of  ingot,  42 
Sponge  gold,  117 

Spoon,  iron,  use  of,  in  molding,  316 
Spring,  correction  of,  in  metal  plate,  566 

for  retention  of  dentures,  400 
Staining  porcelain  teeth,  429 
Standard  clasps,  586 
Star  vulcanite  flask,  503 
Steam,  elastic  force  of,  514 

gauge,  use  of,  on  vulcanizer,  514 
Steel,  143 

aluminum,  146 

blister,  145 

chrome,  145 

copper,  145 

crucible,  145 

hardening  and  tempering  of,  146 

Harveyized,  145 

manganese,  145 

nickel,  145 

percentage  of  carbon  in,  146 

preparation  of,  143 

by  Bessemer's  process,  144 
by  the  cementation  process,  144 
for  razors,  146 
shear,  145 
tempering  of,  148 

alloys  for  use  in,  148 
for  tools^  146 
Stomatitis,  272 


Stomatitis,  treatment  of,  preparatory  to 

inserting  dentures,  272 
String  used  for  outlining  gum  festoon  and 
plate  periphery  in  vulcanite  work,  488 
Sulcus  mento-labialis  as  affected   bj'  loss 
of  the  teeth,  251 
naso-labialis,  252 
Sulphuric  acid  for  pickling,  61 

use  of,  in  opening  root  canals, 
676 
Supporting    abutments    for    removable 

bridges,  757 
Supports  for  melting  metals,  35 
Swaged  metallic  plates,  549 
base-plate,  558 
clasps  for,  583 
for  full  lower  denture,  574 
forming  the  pattern  for,  553 
making    the   backings   for, 

620 
for  partial  upper  cases,  570 

swaging  of,  572 
preparing   the   metal  form 

for,  554 
repair  of,  629 
rim  for,  610 

selection  of  teeth  for,  593 
soldering  of,  626 
taking  bite  for,  592 
teeth  with   cross-pin  to  be 

avoided  for,  594 
trial  of,  in  mouth,  589 
wiring  of,  615 
Swaging  anvil,  26 
block,  26 
force  used  in,  561 
full  lower  plate,  574 
hammers,  27 

manner  of  using  mallet  in,  560 
necessity  for  annealing  in,  560 
occurrence  of  wrinkles  in,  561 
outlining  alveolar  ridge  in  full  upper 
denture  during,  563 
vacuum-cavity  in,  561 
partial  upper  plate,  572 
platinum   for   continuous-gum   den- 
ture, 638 
preliminary  bending  of  plate  before, 

559 
process  of,  559 
protection  of  die  in,  560 
rubber  slabs  for,  24 
use  of  finishing  die  in,  564 
Sweating  seams  of  cap  crowns,  695 

use  of  counter-die  in,  560 
Sylvanite,  HI 

Syno\'ial  sacs  as  lubricants  of  articulation, 
199 


Table  of  elements,  91 
plaster,  27 

accessories  of,  28 
soldering,  45 
Taking  the  bite,  335 

for  a  bridge  with  plaster,  690 


854 


INDEX. 


Taking  the  bite  in  cases  requiriiio:  partial 
dentures,  3.52 
closure  of  the  nioulh  in,  347 
tiata  gainetl  in,  oo() 
difficulties  in,  345 
for  a  full  lower  plate,  351 

upjx'r  i)late,  350 
for  gold  crowns,  use  of  plaster 

for,  mo 

protrusion  of   the   mandible  in, 

347 
rationale  of  method  of,  337 
for  swaged  metallic  plates,  592 
technique  of,  340 
where  the  bite  is  to  be  opened, 
353 
the  remaining  teeth  do  not 
occlude,  352 
occlude    properly, 
353 
Technique  of  taking  full  lower  impression, 
294 
upper  impression,  290 
Teeth,  arch  outline  of,  212 
axes  of,  direction  of,  221 
canine,  occlusion  of,  220 
celluloid,  190 
classes  of,  213 

functions  of,  213 
contact  of,  in  forward  movement  of 

mandible,  223 
continuous-gum,  191 
countersunk  pin,  191 

advantages  of,  191 

cusps  of,   overhanging,   function  of, 

227 

use  of,  in  crushing  food,  227 

deepening   bv   age   of   the   color   of, 

266  ■ 

examination  of  mouth  preliminary  to 

insertion  of,  271 
gum  section,  1S5 

use  of,  1S9 
loss  of,  234 

cause  of,  234 

effect  of,  upon  digestion,  235 

upon  incision,  234 

upon  the  jaws,  235 

upon  mastication,  234 

lower  natural,  articulation  of  upper 

artificial  teeth  to,  453 
natural,  retention  or  extraction  of, 
273 
use  of,   as  substitutes  for  lost 
teeth,  161 
occlusion  of,  213 

bicuspid  and  molar  teeth,  215 
incisor,  214 
physical  characteristics  of,  256 
plain,  189 

advantages  of,  189 
plate,  191 
porcelain,  161 
body  of,  161 
burning  of,  183 
carved,  bodj'  of,  165 


Teeth,  porcelain,  classes  of,  183 
constituents  of,  lti2 
enamels  of,  "base,"  165 

"point,"  165 
finishing  of,  429 
forms  of,  188 

manufacture  of,  colors  in,  165 
molding  of,  ISl 
molds  for,  172,  181 
pinlcss,  18s 
pins  for,  187 
staining  of,  429 
transparency  of,  161 
relative  size  of,  212 
rubber,  190 

"pin"  guard  of,  190 
saddle-back,  191 
surfaces  of,  occlusal,  211 
surgical   complications   affecting   in- 
sertion of,  277 
table  of  temperamental  characteris- 
tics of,  262 
tube,  191 
variations  in  size,  shape,  and  color 

of,  255 
wear  of,  227,  267 
Telescope  crown,  749 

cap  for,  inner,  750 

outer,  750 
contour  for,  751 
cusp  for,  751 
material  for,  750 
preparation  of  tooth  for,  749 
Temperament,  256 

basal  types  of,  259 
bilious,  256 
diagnosis  of,  259 

a  guide  in  selecting  color  for  arti- 
ficial teeth,  409,  412 
lymj^hatic,  258 
nervous,  258 
sanguine,  257 
Tem])eramental  characteristics  of  teeth, 
tableof,  262,  264 
compounds,  table  of,  260 
Tempering  alloys,  106 
of  excavators,  148 
of  rubber-dam  clamps,  148 
of  steel,  147 
Temporary  dentures,  bite-plates  for,  351 

importance  of  inserting,  277 
Temporo-mandibular    articulation,     196, 
345 
ligaments  of,  199,  346 
Tenacity  of  alloys,  104 

of  metals,  95 
Testing  of  crucibles,  40 
Thermometer  for  vuleanizer,  515 
Time  regulator  for  vuleanizer,  512 
Tin,  156 

action  of  acids  and  alkalies  on,  157 

alloys,  of,  157 

casts,  157 

core  for  weighted  vulcanite  denture, 

536 
cry,  156 


INDEX. 


855 


;Tin,  deposition  of,  158 
(lioxidc,  157 
foil,  157 

upplication  of,  to  wax  model  of 

vulcanite  i)late,  4SS 
use  of,   in  forming  pattern  for 
metal  ]jlate,  553 
in  vulcanite  work,  483 
fueing  point  of,  157 
occurrence  of,  15G 
jiroperties  of,  156 
Tinstone,  156 
Tinting   and    staining    porcelain    teeth, 

429 
Titanium  oxiile,  use  of,  in  porcelain  teeth, 

165 
Tomes,  Sir  John,  on  absorption  of  the 

process  of  mandible,  238 
Tongs,  solder,  61,  62 

Tongue,  free  movement  to  be  provided 
with  artificial  dentures  for,  458 
maintenance   of    plate    denture   by, 
388 
Tools  for  bench  work,  88 
care  of,  88,  90 
for  metal  work,  89 
for  molding,  314 
for  vulcanite  work,  90 
Tootn  ut?dv,  materials  of,  16i 
enamel,  maceilll}^  of,  151 
Ti'anslucency  of  porcelain  teeth,  161 
Trays  for  impressions,  287 

molding,  25 
Trimming  plaster  casts,  308 
Trowels  for  use  in  molding,  315 
Trumpet  mouth-piece  for  blowpipe,  46 
Trying  teeth  mounted  on  a  metal  plate 

in  the  mouth,  603 
Tube  and  split-pin    attachment  for  re- 
movable bridges,  754 
for  use  in  removable  bridge- 
work,  758 
of  glass,  use  of,  .in  molding,  315 
teeth,  191 

with  continuous-gum  dentures, 
657 
Turner  gasoline  blowpipe,  53 
Tweezers,  solder,  61 
Type  metal,  150 

u 

Ulsaver,   E.   S.,   on  determining  tooth 

curves  in  bite-plates,  441 
Undercut  model,  securing  mold  from,  324 
mold  of,  with  cores,  327 
use  of  Hawse's  flask  with,  326 


Vacttum  chambers,  397 

advantages  of,  397 
Haskell  on  use  of,  398 
indications  for  use  of,  400 
irritation  caused  by,  397,  779 
location  of,  398 


Vacuum    chambers,    manner  of   making, 
in    metal    plate,    use    copper 
form,  562 
means  of  forming,  in  vulcanite 

plate,  400 
objections  to,  397 
relation  of,  to  speech  production, 

459 
size  and  shape  of,  398 
swaging  of,  in  metal  plates,  561 
thickness  of,  399 
means  of  producing,  in  mouth,  397 
Vanderpoel  on  drawing  and  construction 

of  human  figure,  464 
Varnish,  sandarac,  28,  303 
use  of,  28,  303 
shellac,  28,  303 
making  of,  28 
use  of,  28,  303 
Vela,  construction  of  artificial,  820 
Velum,  functions  of  natural,  789 
Kingsley,  action  of,  790 
description  of,  791 
rationale  of,  792 
obturator  of  Ca^^^-,  789 

advnitages  of,  806 
desr-iiption  of,  804 
fitting  of,  830 
forming  of,  805,  830 
Ottolengui's,  808,  830 
'"Veneers,''  191 
Vermilion,  136 

action  of  acids  on,  137 

as  a  coloring  agent  for  vulcanite,  137 

importance  of  not  using  nitrohydro- 

chloric  acid  upon,  781 
non-injurious  character  of,  481 
non-poisonous  quality  of,  137 
not  decomposable  in  mouth,  781 
preparation  of,  136 
properties  of,  137 
uses  of,  137 

for  coloring  red  rubber,  481 
Verrier's  porcelain  furnace,  64 
Vise  for  wire  drawing,  23 
Vocal  cords,  241 

sound  made  by,  241 
Voice  and  speech,  relation  of,  to  artificial 
dentures,  457 
apparatus  for  production  of,  241 
characteristics  of,  241 
effect  of  loss  of  teeth  upon,  242 
loudness  of,  241 
pitch  of,  241 
quality  of,  241 

slight  alteration  of,  by  artificial  den- 
ture, 457 
Volatility  of  metals,  98 
Vowels,  243 
Vulcan  gold  lining  for  vulcanite  plates, 

532 
Vulcanite,  advantages  and  disadvanta.ges 
of  use  of,  279,  481 
base-plate,  279,  482 

arranging  teeth  on,  486 
finishing  of,  484 


M 


INDEX. 


Vulcanite  bii.sc-i)lato,  finishing  of  niuxil- 
lary  surface  of,  4S3 
flasking  of.  482 
])acking  of^,  484 
vuk^aiiizalion  of,  484 
in  combination  with  plates  of  fusible 

alloy,  527 
composition  of,  475 
Day's  patent  upon,  475 
dentures,  additions  to,  541 
construction  of,  481 
base-plate  in,  482 
casts  for  use  in,  482 
double  vulcanization  meth- 
od, 482 
finishing  of,  493,  500 
for  partial  cases,  49*.) 
full  lower,  double  vulcanization 
method,  498 
single        vulcanization 
method,  499 
upper,  single  vulcanization 
method,  498 
impressions  for,  482 
lined    with    gold    foil,    electro- 
deposits,  etc.,  531 
natural  teeth  in,  524 
partial  lower,  523 

Dashwood's  method  of 
constructing,  524 
removal  of  deposits  ''rom,  780 
repair  of,  538 
rubber  facings  for,  534 
trial  of,  487 
Walker's   granular   gum    facing 

for,  534 
weighted,  535 
discovery  of,  474 
Goodyear  patent  upon,  474 
history  of,  474 
physical  properties  of,  476 
plates,  finishing  of,  S3 
chalk  for,  8() 
porosity  of,  477 
relative  strength  of  various  kinds  of, 

476 
repair  of,  477 

work,  occasional  and  special  methods 
in,  519 
tools  for,  90 
Vulcanization,  chemistry  of,  477 
definition  of,  480 
results  of,  480 

Weber  on,  477 
Vulcanized   rubber   as   a  base   for   arti- 
ficial dentures,  472 
,  Vulcanizers,  507 
cam-lock,  508 
Edson,  508 
Lewis  cross-bar,  508 
method  of  use,  51S 
Seal)ury,  509 
time  regulator  for,  512 
Vulcanizing,  technique  of,  500 


W 

Walker  artic-ulator,  357 

on  coiita('t  of  cusps  in  lateral  excur- 
sion of  mandible,  225 
Warming  oven  for  rubber  and  vulcanite 

flask,  507 
Wax,  adhesive,  86 

cement,  87 

fluxed,  87 

spatula,  87 

used  in  vulcanite  work,  501 
Waxing  up  denture,  88 

burner  for,  88 
Wear  of  teeth,  imitation  of,  426 
Wearing  artificial  dentures  at  night,  777 
Weighted  rubber,  535 
Welding  metals,  97 
White  metal,  152 
Whitney  vulcanite  flask,  504 
Wildman,  enamels  of,  formulas  of,  167 
Wilson,  George  H.,  on  balancing  of  den- 
tures, 445 

on  staining  teeth,  431 

vulcanite  flask,  503 
Wire  clamps  for  soldering,  61 

drawing,  42,  44 
vise  for,  23 

half-round,  drawing  of,  44 

rim  for  full  lower  f;L".tC,  575 

squ^ire,  drawing  of,  44 
■'"  V*  Iring"  full  lower  plate,  575 

swaged  metallic  plates,  615 
Wood  alcohol  in  burner,  56 
Wood's  metal,  formula  of,  155 
Work-bench,  18 

accessories  of,  23 

for  crown  and  bridge-work,  19 

dimensions  of,  18 

for  gold  work,  19,  21,  22 

location  of,  IS 

for  plaster  work,  21,  23 

for  two  workmen,  18 

for  vulcanite  work,  19,  22 
\\'rinkles,  eiTect  of  plate  dentures  on,  471 

occurrence  of,  in  swaging,  561 

par'    1  lower  plates,  580 
Wrought  iron,  14 

properties  of,  143 


Zinc,  152 

action  of  acids  on,  153 

alloys  of,  153 

effect  of  alloying  with  platinum,  153 

exi)ansibility  of,  100 

malleability  of,  153 

occurrence  of,  1.53 

properties  of,  1.53 

union  of  lead  with,  312 

use  of  chemically  pure,  in  gold  s(>lder, 
551 
for  dies,  153,  311 
Zygomatic  column  of  fixed  base,  193 


Dote  Du 


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